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Chapter 25 • Rashes and Skin Lesions 311
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cutaneous anthrax, characterized by lesions that evolve
from a papule, through a vesicular stage, to a depressed
eschar. Sun exposure can also worsen chronic eruptions,
such as rosacea or the malar buttery rash in systemic
lupus erythematosus (SLE). Ringworm is common in
farmers and ranchers who work with cattle.
Pets
Fleabites produce an urticarial lesion with a central punctum. The reaction is an immunological one, making it different in each individual. Bites are usually on the legs. New
lesions may appear daily, and itching is variable but sometimes intense. Fleas on a cat or dog are usually the culprits.
An atypical form of scabies can be transmitted from dogs
to humans and usually presents as a single lesion.
Is there anything that exacerbates or triggers
the reaction?
Key Questions
n Does anything seem to make this worse?
n Do you have any known allergies?
Triggers
Patients often easily identify aggravating factors. Any
rash involving vasodilation will become more vivid
and likely more pruritic with heat exposure, whether
via sunlight, sweating, or a hot shower. Localized
eruptions, especially on the hands or forearms, prompt
many patients to consider chemicals or other products
as causes. Persons with eczema whose hands are frequently exposed to water are vulnerable to the development of irritant eczema on the exposed skin. Foods
occasionally exacerbate skin lesions. Rosacea is a vasomotor instability disorder characterized by exacerbation with dietary consumption of vasodilators, such
as coffee, tea, alcohol, or spicy foods. Stress, whether
physiological (e.g., menstruation, pregnancy) or psychological, is widely believed to trigger or worsen
many chronic rashes, especially eczema and psoriasis.
Stress also may facilitate recurrent eruptions of HSV.
Could this rash be caused by a medication?
Key Questions
n Are you taking any medications (prescription or
over-the-counter medications)?
n Do you have any medication allergies?
n Have you had a recent vaccination?
Medication
There are four types of dermatological effects of drugs:
side effects (e.g., photodermatitis), allergic reactions
(e.g., urticaria, xed drug eruptions, or morbilliform
eruptions), commensal skin eruptions (e.g., pityriasis
versicolor in a patient on systemic corticosteroids), and
worsening of existing skin eruptions (e.g., tinea eruptions mistakenly treated as eczema with topical corticosteroids). Medications used after the onset of a rash
may be irritants or sensitizers and worsen the condition.
Recent Vaccination
Infants and children who have recently had a measles
vaccination may display a rash 10 to 14 days after
immunization.
Is there a signicant dermatological family
history?
Key Question
n Does anyone in your family have chronic skin
problems?
Family History
A family history of dermatological problems may add
insight to the diagnosis. Atopic disease (atopic dermatitis, asthma, hay fever) tends to cluster in families. Psoriasis, seborrheic dermatitis, and rosacea are also frequently noted to have a familial inheritance pattern.
Multiple café au lait spots with a positive family history
for neurobromatosis can help identify children with
this dominantly inherited disease.
DIAGNOSTIC REASONING:
FOCUSED PHYSICAL EXAMINATION
Look at All the Skin and Mucous
Membranes
A “peephole” diagnosis should be avoided; the whole
organ should be examined. If the patient is not fully
undressed, relevant lesions could be missed. However,
it is useful to select one typical well-dened lesion to
describe in detail, followed by an orderly and sequential system of examination so that no areas of the body
are missed. The feet should always be examined in the
presence of hand dermatitis so as not to miss a hypersensitivity reaction to a tinea infection or a concomitant hand tinea. Erythema in dark-skinned persons may
be difcult to appreciate; it often is seen as postinammatory hyperpigmentation.
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Inspect for Distribution
Determine if the lesion is widespread or localized,
unilateral or bilateral, symmetrical or asymmetrical.
Symmetrical lesions commonly have internal causes
(e.g., eczema, psoriasis, acne); asymmetrical lesions
have external causes (e.g., bacterial or fungal infections,
allergic contact eczema). Is the lesion predominantly on
the exor (as in atopic eczema) or extensor (as in psoriasis) surfaces? A rash on the soles or palms occurs with
erythema multiforme and rickettsial infections. Determine if the distribution is conned either to protected
areas or to light-exposed areas, such as in collagenvascular diseases, photosensitive reactions to drugs, and
airborne contact dermatitis. Is the lesion predominantly
centri fugal (affecting the extremities, as seen in erythema
multiforme, Rocky Mountain spotted fever, and insect
bites) or centripetal (sparing the extremities and concentrated on the trunk)? Intertriginous distribution (neck,
axilla, groin) is found in candidiasis, some inammatory
fungal infections, and some forms of psoriasis.
Inspect the Mouth
Drug eruptions from sulfonamides, penicillin, streptomycin, quinine, and atropine often have associated
mucosal erosions and crusts. Mucosal involvement is
common in hand and foot lesions (e.g., hand-foot-andmouth disease), herpes, and syphilis.
Inspect the Hair
In children, a triad of hair loss, scaling, and lymphadenopathy is diagnostic of tinea capitis. A high index of
suspicion is warranted in inner-city urban areas, where
the condition is common.
Palpate the Skin
Palpate skin lesions to assess for tenderness, texture and
consistency, rmness, uctuance, and depth. Smooth
skin has no irregularity. Uneven skin has ne scaling or
some warty lesions. Rough skin feels like sandpaper and
is characteristic of keratin/horn or crusts. Assessing the
supercial skin for texture is done by palpation with the
ngertips. Deeper palpation is done using the thumb and
index ngers. Soft skin feels like the lips, normal skin
like the cheeks, rm skin like the tip of the nose, and hard
skin like the forehead. The depth of the lesion determines
if it is on the surface or located within the dermis or the
subcutaneous tissue. An indurated base is a thickening in
the depths of the lesion rather than on the surface.
Palpate the Regional Lymph Glands
Many viral exanthems present with rash and lymphadenopathy. Palpation of the regional lymph glands may be
of assistance in the diagnosis if neoplasm is suspected.
Perform an Abdominal Examination
The detection of hepatic or splenic enlargement may assist in the diagnosis of a systemic cause of skin disorders.
LABORATORY AND DIAGNOSTIC STUDIES
Diascopy
Diascopy is used to assess for blanching on pressure
and is accomplished by pressing a glass or clear plastic
slide on the lesion. Diascopy is most helpful in evaluating purpuric lesions: blood that is outside vessels (as in
petechiae) will not blanch, whereas that entrapped
within dilated vessels (as in telangiectasias) will demonstrate this phenomenon.
Wood’s Light
Long-wave ultraviolet (UV) light is used in the diagnosis of lesions caused by fungal infections. Many,
but not all, fungal rashes uoresce. Trichophyton,
dermatophytes that are frequently identied in tinea
eruptions, do uoresce; Microsporum, which can also
be responsible for tinea eruptions, do not.
Skin Scraping and Potassium Hydroxide
Preparation
Microscopically examine a sample of cells retrieved
from a lesion, assessing for the presence of fungal or
dermatophytic spores and hyphae. The lesion should be
gently scraped using a scalpel (collect cells from an active area such as the border of the lesion); the cells are
treated with a drop of 20% potassium hydroxide (KOH)
and then warmed or allowed to stand a few minutes to
soften the keratin. The addition of 40% dimethyl sulfoxide (DMSO) to the KOH solution accelerates diagnosis.
Chlorazol Black E stain highlights fungal hyphae as
dark blue-black against a light gray background.
Tzanck Smear
In a Tzanck smear, an indirect test for herpesvirus infections (HSV, HZ), cells are retrieved by swabbing the
base of a lesion (usually a vesicle), smearing it onto a
glass slide, and then staining it with Giemsa or Wright
solution. Examined microscopically, the presence of
multinucleated giant cells conrms the diagnosis.
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Bacterial Culture
In taking a bacterial culture, exudate from a lesion is
collected on a sterile swab and then cultured for
growth. Gram stain may also be done. When a bacterial
isolate is known, antibiotic sensitivity testing is performed.
Viral Culture
For a viral culture, cells from the base of a lesion (usually a vesicle) are collected on a Dacron swab and
cultured for identication of viral infections, particularly HSV or HZ.
Punch Biopsy
In a punch biopsy, a tissue sample is assessed histopathologically for identication. Select a punch size
about 2 to 3 mm larger than the lesion or sample an
active area if the lesion is large. Gently swirl while
exerting slight downward pressure on the punch. When
well into the dermis, remove the punch and excise the
sample at its base. The defect may be closed with electrocautery or suture(s) or left open to heal by second
intention. Place the sample in a preservative such as
formaldehyde solution.
Excisional Biopsy
In excisional biopsy, a tissue sample is assessed histopathologically for identication. Excise the entire lesion,
usually making an elliptical incision around the lesion
beyond its margins. Excise the base and close the defect
with sutures or cauterize bleeding vessels. Place the
sample in preservative.
DIFFERENTIAL DIAGNOSIS
The following conditions represent many of the most
common skin eruptions observed in primary care. Consult
a dermatology text for a complete review.
beyond 12 months may indicate endocrine dysfunction.
African Americans and other dark-skinned persons
need aggressive treatment to prevent postinammatory
hyperpigmentation.
Rosacea
Rosacea is a vasomotor instability disorder characterized by sebaceous gland hypertrophy, papules, pustules,
persistent erythema, and telangiectasias. It shows a
predilection for the face.
Infectious Eruptions
Impetigo
Impetigo presents as a supercial pustular, bullous, or
nonbullous eruption, followed by crusting (often honey
colored). The causative organism is usually Staphylo-
coccus or Streptococcus. Contagion occurs via direct
inoculation. It is typically a localized eruption that can
occur anywhere on the body, with a predilection for the
face and trunk.
Folliculitis
Folliculitis is a supercial pustular infection of the hair
follicles. Causative organisms are usually Staphylococ-
cus and occasionally Streptococcus or gram-negative
organisms, including Pseudomonas, Klebsiella, and
Proteus. It is typically a localized eruption that can occur anywhere on the body, with a predilection for hairy
areas and exural regions.
Furuncle
A furuncle, often referred to as a boil, is a more
extensive infection secondary to a folliculitis (see
Folliculitis).
Carbuncle
A carbuncle is an abscess of conjoined or adjacent
furuncles (see Furuncle).
Follicular Eruptions
Acne Vulgaris
Acne presents as a chronic eruption of the pilosebaceous
unit, with noninammatory lesions (open or closed
comedones) and/or inammatory lesions (e.g., papules,
pustules, cysts), and is most commonly a problem of
adolescents. Its distribution follows that of the sebaceous glands: face, neck, chest, back, and upper arms.
Neonatal acne rst occurs between 2 and 4 weeks
of age, lasting until 4 to 6 months of age. Persistence
Macular and Papular Eruptions
Erythema Infectiosum (Fifth Disease)
Fifth disease, also known as slapped cheek disease,
presents as a systemic illness of sudden onset characterized by a coalescing, red, maculopapular eruption on
the face. A reticular eruption occurs on the extremities
2 to 3 days later. The causative organism is parvovirus
B19. This is a self-limiting condition.
Children with underlying hemolytic anemia may
experience an aplastic crisis.
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Measles (Rubeola)
Measles are caused by a viral exanthem, and the systemic
illness that results is characterized by a ne, erythematous, morbilliform eruption on the face that spreads
rapidly to the trunk and becomes conuent and reticulate.
Cough, purulent coryza, photophobia, and fever precede
the rash. This is a self-limiting condition.
Rubella
Rubella results from a viral exanthem similar to
measles and starts as ne macules and papules on the
face and progresses caudally. Lymphadenopathy of
postauricular nodes is characteristic of this disease.
Pityriasis Rosea
Pityriasis rosea presents with a rapidly evolving papulosquamous eruption of possible viral etiology. An initial
“herald patch” is characteristic, followed within days by
numerous faintly erythematous patches on the trunk and
upper extremities (“T-shirt and shorts” distribution). The
patches demonstrate ne scaling, and mild to severe
pruritus may be present. It is more common in the spring
and fall and among adolescents. In African American
children, the eruption may consist only of occasional
oval lesions along the cleavage lines. The remaining
lesions are discrete, scattered follicular or nonfollicular
papules over the trunk and proximal extremities. The
face may also be involved.
Vesicular and Bullous Eruptions
Hand-Foot-and-Mouth Disease
Coxsackievirus A16 is the causative organism of this
viral exanthem and systemic illness. Painful mouth
ulcers followed by painful white vesicles with a surrounding erythema on the ngers, palms, toes, and
soles characterize the condition. Patients usually have
a low-grade fever, sore throat, and malaise for 1 to
2 days. Some develop submandibular or cervical
lymphadenopathy. This is a self-limiting condition.
Insect Bites
Mosquito and horsey bites can cause a common blistering reaction that is surrounded by faint erythema,
central pallor if swollen, and usually a visible central
punctum. The bites may be arranged in groups if they
are multiple. The lesions are pruritic and/or sore; the
condition is self-limiting. The deer tick bite causes a
bull’s-eye rash at the site of the bite.
Herpes Simplex Virus
HSV lesions have vesicles (solitary or grouped) that
are surrounded by an erythematous base, with discrete,
well-demarcated areas that later crust. The condition is
associated with soreness and/or pain and may be preceded by tingling. There is a predilection for lips and
genitalia. Recurrences in the same location are common and usually milder.
Scarlet Fever
Scarlet fever is a systemic illness associated with group
A ß-hemolytic Streptococcus (GABHS) (strep throat).
It is characterized by a macular erythema of the face
(ushing), except around the mouth (circumoral pallor),
followed by a disseminated ne papular erythema
(scarlatiniform), which may then desquamate. The rash
is intensied in the exor folds (Pastia lines). Associated symptoms are sore throat, malaise, fever, circumoral pallor, and a white or strawberry tongue.
Roseola
Roseola is a viral infection caused by human herpesvirus 6 (HHV-6). It is characterized by 2 to 3 days of
sustained fever in an irritable infant who otherwise appears well. Mild edema of the eyelids and posterior
cervical lymphadenopathy are occasionally seen. After
the patient’s temperature decreases, a pink, morbilliform, cutaneous eruption appears transiently and fades
within 24 hours. This is a self-limiting condition.
Herpes Zoster (Shingles)
HZ lesions present as clustered vesicles that are surrounded by an erythematous base, with discrete, welldemarcated lesions that later crust. Intense burning and
pain often precede the eruption. There is a predilection
for dermatomal distribution.
Varicella Zoster (Chickenpox)
Varicella lesions are discrete vesicles with a disseminated distribution; lesions develop in crops or in
succession. Vesicles later crust, and occasionally
secondary impetigo develops. The illness is associated with malaise and fever. This is a self-limiting
condition.
Fungal Infections
Candidiasis
A yeastlike fungus that produces rashes at a variety of
sites causes candidiasis; these rashes are called vulvovaginitis, thrush, intertrigo (groin, axilla, gluteal), and
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diaper dermatitis. The lesion is an erythematous maculopapular eruption that is well demarcated, occasionally with satellite lesions (pinpoint papules) at the periphery with maceration in moist areas. It is associated
with mild to intense pruritus; the causative organism
usually is Candida albicans.
Tinea
Tinea is a fungal eruption that causes rashes at a variety of sites: body (corporis), foot (pedis), beard (barbae), groin (cruris), and scalp (capitis). Lesions have
erythematous scaling areas with a discrete border and
central clearing that is often associated with pruritus or
soreness. The causative organisms are Trichophyton,
Microsporum, and Epidermophyton.
Pityriasis (Tinea) Versicolor
Pityriasis versicolor is a yeast infection characterized
by a macular eruption of many colors, hypopigmentation to hyperpigmentation, and ne scaling. Macules begin insidiously, may take weeks to months to
fully develop, and may coalesce. The condition is
usually asymptomatic but occasionally pruritic.
There is a predilection for a sebaceous gland distribution (neck, trunk). The causative organism is Pity-
rosporum orbiculare (Malassezia furfur). Repigmentation may take years or may never occur. Recurrences
are common.
Immunological and Inflammatory
Eruptions
Eczema
Eczema is a chronic relapsing inammatory condition
that can take several forms (atopic, nummular, or dyshidrotic). Eczema is characterized by erythematous
macules, papules, and vesicles that occasionally weep
and/or crust. When severe, eczema may be associated
with ssuring and bleeding. It is associated with mild
to intense pruritus. In dark-skinned persons, scaling
and dryness associated with eczema give an “ashy”
appearance to the skin.
Contact/Allergic Dermatitis
Contact dermatitis is an inammatory reaction to many
substances (e.g., poison ivy, nettles). Papulovesicular
or bullous eruption surrounded by erythema, with
weeping of exudate (noncontagious), is characteristic
of the condition. It may be associated with moderate to
intense pruritus.
Psoriasis
Psoriasis is a chronic, relapsing autoimmune disorder
characterized by well-demarcated erythematous plaques,
patches, and papules, which typically present with silvery scales. There is a predilection for the elbows,
knees, hands, nails (pitting), scalp, and gluteal cleft. The
condition may be pruritic or sore. The lesions may demonstrate Auspitz sign: pinpoint bleeding when the surface is scraped.
Seborrheic Dermatitis
Seborrheic dermatitis is a chronic, relapsing disorder
characterized by erythematous scaling patches, which
are poorly demarcated and may be pruritic. There is a
predilection for the scalp, face, central chest, and genitals. The condition is aggravated by cold weather, dry
skin, and stress.
Allergic Reactions
Erythema Multiforme
Erythema multiforme is an immune complex disorder
involving the skin and occasionally the mucous membranes. Iris (target) lesions appear on the extremities and
desquamation often follows. Common causes include
medications (especially sulfonamides, penicillins, barbiturates, salicylates), histoplasmosis, mycoplasma, HSV,
mononucleosis, hepatitis B, and malignancies. It is often
self-limited. A severe form, Stevens-Johnson syndrome,
is characterized by widespread involvement with vesicobullous lesions. It involves the mucous membranes,
conjunctiva, and urethra, and also can involve the lungs,
gastrointestinal tract, and kidneys.
Urticaria
Urticaria is characterized by a well-demarcated, usually disseminated, eruption that is evanescent over
minutes to about 24 hours. The condition usually has
an asymmetrical distribution.
Neoplastic Eruptions
Malignant Melanoma
Melanoma is an aggressive cancer with a tendency to
spread rapidly and metastasize early. Characterized by
asymmetry (half of a mole or lesion does not look like
the other half), melanoma has an irregular, scalloped,
or not clearly dened border with a color that varies or
is not uniform (whether the color is tan, brown, black,
white, red, or blue). The diameter is usually larger than
6 mm. However, any change in the size of a mole
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should be viewed with suspicion. The three most signicant risk factors for the development of melanoma
include history of melanoma in a rst-degree relative,
a large number of moles (more than 50 to 100), and
atypical moles as designated by biopsy. Other factors
that increase the risk of melanoma include adulthood,
blond or red hair, blue or light-colored eyes, changed
to reach a diameter of 1/2 inch. Untreated, the carcinoma
will begin to bleed, crust over, and then repeat the cycle.
Although this type of cancer rarely spreads to other parts
of the body, it can extend below the skin to the bone and
cause considerable local damage. The cure rate for basal
cell carcinoma (sometimes referred to as nonmelanoma
carcinoma) is 95% when properly treated.
or persistently changing mole, Caucasian race, fair
complexion, freckles, personal history of melanoma,
immunosuppression, inability to tan, severe sunburns
in childhood, and presence of a congenital mole.
Squamous Cell Carcinoma
Squamous cell carcinoma presents as an indurated
papule, plaque, or nodule with a thick scale that is of-
ten eroded, crusted, or ulcerated. It can be found on
Basal Cell Carcinoma
Basal cell carcinoma usually appears as a small, eshy
bump or nodule on the head, neck, or hands. Occasionally, these nodules may appear on the trunk of the body,
usually as at growths. These basal cell tumors do not
spread quickly. It may take many months or years for one
sun-exposed skin surfaces, in areas of radiodermatitis,
or on old burn scars. Although slow growing, squa-
mous cell carcinomas arising on the lip, mouth, or ears
may be associated with regional lymphadenopathy and
metastasis. If promptly and properly treated, it has a
cure rate of 95%.
DIFFERENTIAL DIAGNOSIS OF Common Causes of Rashes and Skin Lesions
CONDITION CHARACTERISTICS
DISTRIBUTION/
PROGRESSION ASSOCIATIONS
DIAGNOSTIC
STUDIES
Follicular Eruptions
Acne
vulgaris
Rosacea Flushing, persistent
Infectious Eruptions
Impetigo Vesicular infection;
Folliculitis Superficial perifollicular
Furuncle Very tender, deep-
Carbuncle Multiple coalescing
Comedones and/or
papules, pustules,
cysts
redness, sebaceous hyperplasia, erythematous
papules, telangiectasias, ocular involvement
in up to 40%
honey-colored crusts
and erosions
papules and pustules
seated inflammatory
nodule that develops
from folliculitis
furuncles
Face, neck, back, chest,
upper arms
Symmetrical, usually
face only; may involve
eyes
Face; any area of body
with a minor wound,
especially excoriated
lesions
Any hair-bearing body
surface, but especially
scalp, beard, legs,
axillae
Same as folliculitis May have fever Incision and
Same as furuncle Same as furuncle Same as
Onset of puberty, topi-
cal steroids, anabolic
steroids, systemic corticosteroids, lithium,
phenytoin
Topical steroids,
systemic
corticosteroids
Scratching as a result
of insect bites, atopic
dermatitis, scabies
Shaving, hot tubs,
contact with mineral
oils, occlusive
dressings
Usually none
Usually none
Bacterial culture
Bacterial culture
drainage
for bacterial
culture
furuncle
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DIFFERENTIAL DIAGNOSIS OF Common Causes of Rashes and Skin Lesions—cont’d
CONDITION CHARACTERISTICS
Macular/Papular Eruptions
Erythema
infectiosum
Measles Patient develops three
Rubella Tender lymphadenopa-
Pityriasis
rosea
Scarlet fever Fine, mildly
Roseola High fever for 3-4 days
Bright-red rash or
“slapped cheeks,”
followed by diffuse
maculopapular rash on
trunk and extremities,
leading to a lacy
appearance as
exanthem fades
Cs: cough, coryza, and
conjunctivitis; Koplik
spots are evident on
buccal mucosa; rash
begins with spike of
convalescent fever;
rash is centripetal in
distribution, possibly
becoming hemorrhagic
in severe cases
thy of postauricular,
posterior occipital
nodes; maculopapular
and confluent rash that
is lacy and not pruritic;
rash lasts 3 days
Multiple oval
erythematous lesions
with an inner fine circle
of scale; ovals line up
along skin cleavage
lines on trunk,
producing a Christmas
tree–like pattern
erythematous papules
and sandpaper-like
rash found on trunk
in infants and young
children; as fever
returns to normal, a
diffuse maculopapular
rash erupts
DISTRIBUTION/
PROGRESSION ASSOCIATIONS
Cheeks, then trunk and
extremities
Rash starts on neck
and ears faintly, then
covers face, arms,
and chest; on second
day rash covers lower
torso and legs; on third
day rash is on feet and
face; rash begins to
fade on the fourth day
Rash begins on face and
spreads to trunk and
extremities within first
24 hr
Trunk, proximal
extremities, rarely on
face; rash is preceded
by a “herald patch,”
appearing from a few
days to 3 wk before
generalized eruption
Rash begins in axillae,
groin, and neck; it
avoids face, but there
is circumoral pallor
Rash begins on trunk
and quickly spreads
to arms, face, neck,
and legs
Aplastic anemia in
children with
underlying hemolytic
anemias; fetal hydrops
has been reported in
pregnant women
infected with
parvovirus B19
Abdominal pain,
otitis media, and
bronchopneumonia
are commonly
associated; severe
cases can cause
encephalomyelitis
Infection with virus while
pregnant results in
congenital rubella
More common in spring
and fall
Strawberry tongue; Pas-
tia lines: areas of linear
hyperpigmentation in
deep creases
Posterior cervical
lymphadenopathy
DIAGNOSTIC
STUDIES
IgM, IgG can be
IgM can be
Confirmation
If present on
Culture for
None
measured
measured for
measles as
well as acute
and IgG titers
by acute and
convalescent
IgG titers
or by direct
measurement
of rubella IgM
antibody
palms and/
or soles and
history warrants, check
RPR to rule
out secondary
syphilis
group A
Streptococcus
Continued
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DIFFERENTIAL DIAGNOSIS OF Common Causes of Rashes and Skin Lesions—cont’d
DISTRIBUTION/
CONDITION CHARACTERISTICS
Vesicular and Bullous Eruptions
Hand-foot-
and-mouth
disease
Insect bites Flea, tick bites most
Herpes
simplex
virus
Herpes
zoster
Varicella
zoster
Fungal Infections
Candidiasis Beefy-red, well-
Systemic illness caused
by coxsackievirus A16;
painful white vesicles
with surrounding red
halo
common; intensely
pruritic eruption,
usually in groups of
three; bull’s-eye rash
Primary infection with
grouped vesicles on
an erythematous base
at site of inoculation;
regional lymphadenopathy; may be preceded
by prodrome of
tingling, itching,
burning, or tenderness
Unilateral pain, itching,
or burning preceded
by 3-5 days of eruption of vesicles or
bullae; followed by
crusting and erosions
Generalized pruritic
vesicular lesions that
are in different stages
of healing; erythematous vesicles, ruptured
vesicles, and crusted
vesicles with scabs
demarcated plaques,
often with scaling edge
and satellite lesions;
intertriginous areas
may also show erosions and
maceration
PROGRESSION ASSOCIATIONS
Painful mouth ulcers
followed in 24 hr by
painful vesicles on
fingers, palms, toes,
and soles
Lower legs, but may
appear anywhere on
body if pets allowed
on furniture or beds
Can occur anywhere
on body, but most
common areas are
genitals and thighs,
mouth, lips, and chin;
may be disseminated
in patients who are
immunocompromised
Can occur anywhere on
body, but is unilateral,
following a dermatomal pattern; requires
prompt referral to
ophthalmologist if eye
involved (Note: see
lesion on tip or side of
nose for indication)
Lesions usually begin
on trunk and spread
to face and proximal
extremities
Diaper area in infants,
body folds, mucosal
surfaces, nails, and
nail folds
Low-grade fever, sore
throat, and malaise;
cervical and submandibular lymphadenopathy possible
Exposure to dogs or
cats or to carpeted
areas previously in
contact with infected
animals; outdoor
exposure
Other STDs, HIV;
triggered by sun,
stress, fatigue, fever,
trauma
Immunosuppression,
older age, local
trauma in children
Herpes zoster occurs
with reactivation of
virus
Immunocompromised,
diabetes, steroid
inhalants, pregnancy,
oral contraceptives,
antibiotics, systemic
and topical steroids
DIAGNOSTIC
STUDIES
Tzanck smear
Confirmatory
biopsy
occasionally
needed
Tzanck smear,
viral culture;
screen for
other STDs,
HIV if history
warrants
Viral culture (not
Tzanck smear)
ELISA titers can
confirm acute
infection
KOH, culture
Chapter 25 • Rashes and Skin Lesions 319
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DIFFERENTIAL DIAGNOSIS OF Common Causes of Rashes and Skin Lesions—cont’d
CONDITION CHARACTERISTICS
Tinea Variable, depending on
body part affected;
hair: scaling, hair loss,
pustules; skin: red,
scaly patch that may
develop central
clearing; feet: vesicles
or bullae
Pityriasis
(tinea)
versicolor
Immunological/Inflammatory Eruptions
Eczema/
atopic
dermatitis
Contact/
allergic
dermatitis
Psoriasis Well-demarcated,
Seborrheic
dermatitis
Allergic Reactions
Erythema
multiforme
Variably colored white
to pink to brown
scaling, round or oval
macules of varying
sizes; often coalescing
to form large areas of
discoloration
Erythema, papules,
vesicles, scaling,
excoriations, crusts,
pruritus always
present
Vesicles and erosions
with edema and
inflammation, giving
way to crusts and
lichenification; pruritus
ham-colored plaques
and papules with
silvery scale; chronic,
recurrent pruritus is
common
Chronic scaling, flaking,
erythematous
dermatitis; variable
pruritus
Hypersensitivity reaction
seen as annular target
or iris lesions
DISTRIBUTION/
PROGRESSION ASSOCIATIONS
Skin, hair, feet, nails Immunocompromised,
systemic corticosteroids, farmers and
others with animal
contact, hot humid
weather with tight
clothing or occlusive
footwear
Upper trunk, axillae,
neck, upper arms,
abdomen, thighs,
genitals
Symmetrical; infant:
face, flexures; children:
flexural creases; adults:
may be discrete round
patches or be regionalized to specific area
Localized, often asym-
metrical; may be
generalized with
airborne allergens/
poison ivy; linear
pattern with plant
dermatitis
Favors elbows and
knees, scalp;
intertriginous areas
may involve nails
Areas where sebaceous
glands are most active:
face, scalp, eyebrows,
eyelashes, body folds,
ear folds, presternal
area, mid and upper
back, genitalia
Begins on upper
extremities and trunk
Heat, humidity, tropical
climates, exercise,
systemic corticosteroids, seborrheic
dermatitis
Personal or family
history of asthma,
seasonal allergies, and
eczema; secondary
colonization with
S. aureus or HSV
Occupational,
recreational pursuits
Streptococcal infection,
arthritis, HIV infection,
medications, alcohol,
family history
Atopic history,
HIV infection
Herpesvirus,
Mycoplasma
pneumoniae
infections, drugs
(especially
sulfonamides)
DIAGNOSTIC
STUDIES
KOH, culture
KOH shows
Serum IgE;
Patch testing
ASO titer or
HIV if indicated
Skin biopsy
hyphae and
spores in
“spaghetti
and meatballs” pattern
culture for
bacteria
or HSV if
indicated
strep culture if
indicated; HIV
if indicated;
biopsy
may assist
in diagnosis
if caused
by StevensJohnson
syndrome;
chest film for
Mycoplasma
Continued
320 Chapter 25 • Rashes and Skin Lesions
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DIFFERENTIAL DIAGNOSIS OF Common Causes of Rashes and Skin Lesions—cont’d
DISTRIBUTION/
CONDITION CHARACTERISTICS
Urticaria Transient wheals that
may be acute or
chronic (lasting .6
wk); individual lesions
tend to come and go
within hours; pruritic
Neoplastic Eruptions
Malignant
melanoma
Basal cell
carcinoma
Squamous
cell carcinoma
ELISA, enzyme-linked immunosorbent assay; HIV, human immunodeficiency virus; HPV, human papillomavirus; HSV, herpes simplex virus;
KOH, potassium hydroxide; PUVA, psoralen plus ultraviolet A (light therapy); RPR, rapid plasma regain; SLE, systemic lupus erythematosus;
STD, sexually transmitted disease.
Asymmetrical border,
irregular, has color
variation within lesion
and is .6 mm
Papular or nodular
lesions, with raised
pearly borders and
numerous superficial
telangiectases
Indurated papule,
plaque, or nodule; may
be eroded, crusted, or
ulcerated
PROGRESSION ASSOCIATIONS
Localized, regional, or
generalized
Anywhere on body,
including scalp
Sun-damaged areas;
also seen in covered
areas when there is
genetic predisposition
to basal cell carcinoma
Sun-damaged areas,
areas of radiodermatitis, old burn scars;
can occur anywhere
on body
Angioedema may also
be present, may be life
threatening; chronic
infection, SLE, lymphoma
Usually asymptom-
atic, unless bleeding,
ulceration, discharge
present
Usually asymptomatic Skin biopsy
Usually asymptomatic;
can be associated
with HPV, immunosuppression, topical
nitrogen mustard, oral
PUVA, chronic ulcers,
industrial carcinogens,
arsenic
DIAGNOSTIC
STUDIES
Biopsy; gen-
eral medical
workup to
rule out
underlying
systemic
disease in
chronic
urticaria
Skin biopsy,
excisional
biopsy
Skin biopsy,
excisional
biopsy
REFERENCES AND READINGS
Ely JW: The generalized rash part II: Diagnostic approach, Am Fam
Physician 81:735, 2010.
Gable EK: Pediatric exanthems, Prim Care 27:353, 2000.
Goroll AH, Mulley AG: Primary care medicine, ed 6, Philadelphia,
2009, Lippincott Williams & Wilkins.
Jackson R et al: The diagnosis of skin disease, Dermatol Nursing
11:275, 1999.
Jaffe R: Atopic dermatitis, Prim Care 27:503, 2000.
McKinnon HD: Evaluating the febrile patient with a rash, Am Fam
Physician 62:804, 2000.
Morgan-Glenn P: Scabies, Pediatr Rev 22:322, 2000.
Reifsnider E: Common adult infectious skin conditions, Nurse Pract
22:17, 23, 26, 1997.
Sanlippo AM, Barrio V, Kulp-Shorten C, Callen JP: Common
pediatric and adolescent skin conditions, J Pediatr Adolesc
Gynecol 16:5, 2003.
Wolff TA, Tai E, Miller T: Screening for skin cancer: update of the
evidence, Ann Intern Med 150:194, 2008.
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