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132 Textbook of Diagnostic and Therapeutic Procedures in Allergy
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normal control. A greater histamine release implies that the patient has an autoimmune basis for the
urticaria.
Basophil Activation Test (BAT)
The basophil activation test is an in vitro test that uses flow cytometry to assess donor basophil
activation markers (CD63 or CD203c) in response to stimulation with the patient’s serum. A positive
basophil test has been linked to longer disease duration, higher disease activity and a poor response
to both antihistamines and omalizumab (Iqbal et al. 2012). However, the utility of this test is limited
by several technical challenges. First, basophils from individual donors vary in response to the same
serum over time. Second, different laboratories using different basophil donors will yield different
results. Third, there are no standardized procedures for handling basophils.
Assessment of Disease Activity, Impact and Control
Urticaria, both acute and chronic, can be debilitating. Therefore, periodic assessments should
be made to evaluate disease activity, its impact on quality of life and disease control. Validated
patient-reported outcome measures, such as the Urticaria Activity Score (UAS7), the Angioedema
Activity Score (AAS), the Urticaria Control Test (UCT) and the Angioedema Control Test (AECT)
can be used for this purpose.
UAS7 is a daily personal assessment of both wheals and pruritus measured on a scale of
0–3 over seven consecutive days. AAS assesses daily angioedema activity, scored from 0–15.
Patients who experience hives and angioedema should use UAS7 and AAS in combination
(Figure 4).
To assess disease control, the UCT is used in patients who experience hives (Figure 5A). It is
a four-item questionnaire scored 0–4 with a recall period of 4 weeks. A score of < 12 is indicative
of poor control whereas a score of ≥ 12 is indicative of good control. For patients who experience
angioedema, the AECT should be used (Figure 5B). A score of < 10 is indicative of poor control
Figure 4. The urticaria activity score (UAS) and AAS for assessing disease activity in CSU. Source: Zuberbier et al. 2022.
Acute and Chronic Urticaria/Angioedema 133
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Figure 5. (A) The UCT and (B) The AECT. Source: Zuberbier et al. 2022.
whereas a score of ≥ 10 is indicative of good control. Patients who experience both hives and
angioedema should use UCT and AECT in combination.
Treatment
Basic Considerations
The treatment of acute and chronic urticaria is the same, regardless of whether hives, angioedema
or both are involved. The primary goal is to achieve complete symptom control and normalize the
quality of life. This is achieved by first providing reassurance and education. It is important to
convey to patients that urticaria and angioedema are self-limited in most cases and rarely associated
with a serious underlying disease. Although there is no definite cure, symptoms can be adequately
controlled with pharmacotherapy in most cases. Triggering or exacerbating factors should be
minimized to the extent possible. These include physical factors, NSAIDs, alcohol, stress and
concomitant infections.
Pharmacotherapy
Current EAACI/GA²LEN/EDF/WAO guidelines propose a stepwise treatment algorithm (Figure 6)
(Zuberbier et al. 2022). The overall goal of these treatments is to achieve complete symptom control.
Consequently, pharmacological treatment should be continuous rather than on demand. However,
symptoms should be reassessed at least once every 3–6 months, and treatment adjusted accordingly.
Second-Generation H1-Antihistamine
Initial treatment consists of a nonsedating, second-generation H1 antihistamine at a standard
therapeutic dose. Examples include loratadine, desloratadine, fexofenadine, cetirizine and
levocetirizine. Individual responses to a given antihistamine may vary. First-generation antihistamines
are no longer recommended, as they possess anticholinergic and sedative effects, and can negatively
impact REM sleep and school/work performance.
If the standard dose is not effective after 2–4 weeks of continuous use, a four-fold dose
escalation is recommended before other treatments are considered. In this situation, twice-daily
dosing is preferred. Combining different second-generation H1-antihistamines is not recommended.
Although medications are best avoided during pregnancy and breastfeeding, there have been no
reports to date of second-generation antihistamines causing birth defects.
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Figure 6. Recommended treatment algorithm for urticaria. Source: Zuberbier et al. 2022.
Omalizumab
Omalizumab, a monoclonal anti-IgE antibody, is approved in most countries for the treatment of
chronic urticaria in patients ≥ 12 yrs of age who experience insufficient benefit from 2nd generation
H1-antihistamine therapy. A meta-analysis of seven randomized trials involving 1,312 patients
demonstrated a significant reduction in weekly itch and wheal scores with omalizumab relative
to placebo in patients unresponsive to H1-antihistamines (Zhao et al. 2016). Analyses of different
doses showed that 300 mg every 4 weeks was the most effective dose, at which 36% of patients
achieved a complete response (UAS7 score of 0). However, omalizumab does not have long-term
disease-modifying properties, therefore patients may relapse when omalizumab is tapered or
discontinued.
The recommended initial dose is 300 mg subcutaneously every 4 weeks, independent of total
serum IgE and body weight. Second-generation H1 antihistamine therapy is continued but may
be tapered if the patient responds well to omalizumab. As omalizumab carries a small risk of
anaphylaxis (0.2%), patients are advised to carry an epinephrine autoinjector, and the first three
doses are administered in a medical facility where patients are generally monitored for 2 hours.
Patients who are inadequately controlled at the licensed dose of 300 mg every 4 weeks can
be treated with higher doses, shorter intervals, or both. Studies support the use of omalizumab
treatment at doses of up to 600 mg every 2 weeks (Metz et al. 2020). The use of omalizumab in
pregnancy appears to be safe, and to date, there is no indication of teratogenicity.
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Cyclosporine
For patients who do not achieve adequate disease control with a combination of high-dose H1
antihistamines and omalizumab or for patients who do not have access to omalizumab, the calcineurin
inhibitor cyclosporine is the preferred next step. It acts by blocking the calcium-dependent release
of histamine, leukotrienes and other mast cell mediators. Advantages include a rapid onset of
action, a degree of efficacy comparable with systemic corticosteroids and the possibility of lasting
remission after treatment is discontinued. Disadvantages include the potential for hypertension,
renal insufficiency, hirsutism and gingival hyperplasia, although these side effects are less common
at lower doses.
The recommended dose is 3.5–5 mg/kg per day. Blood pressure, blood urea nitrogen and
creatinine should be monitored monthly, while cyclosporine and fasting lipids should be obtained
at baseline and then yearly. After 3 months of complete or near-complete control of symptoms,
the dose of cyclosporine is generally tapered over several months. In most cases, 6–9 months of
treatment is adequate. Although not teratogenic, cyclosporine is embryo-toxic in animal models and
is associated with preterm delivery and low birth weight in human infants. Therefore, the benefits
vs. risks in pregnant women need to be considered on a case-by-case basis.
Systemic Corticosteroids
Systemic corticosteroids may be used short-term to gain temporary control of symptoms during
severe exacerbations, especially if the quality of life is significantly affected. The typical dose of
Prednisone is 20–50 mg daily for 5–10 days. Long-term corticosteroid use is discouraged due to
potential side effects. Topical corticosteroids have not been shown to be beneficial.
Other Treatments
The level of evidence for leukotriene receptor antagonists, H₂-antagonists and Doxepin is low and
therefore is no longer included in the EAACI/GA²LEN/EDF/WAO guidelines. However, these
drugs may still be of value to individual patients in the appropriate clinical context.
Glossary of Abbreviations
AAS – Angioedema Activity Score
ASST – Autologous Serum Skin Test
AECT – Angioedema Control Test
BAT – Basophil Activation Test
BHRA – Basophil Histamine Release Assay
CIndU – Chronic Inducible Urticaria
COX-1 – Cyclooxygenase-1
C4 – Complement Component 4
CSU – Chronic Spontaneous Urticaria
EAACI – European Academy of Allergology and Clinical Immunology
EDF – European Dermatology Forum
FcεR1 – High-Affinity IgE Receptor
GA²LEN – Global Allergy and Asthma European Network
NSAID – Non-Steroidal Anti-Inflammatory Drug
TPO – Thyroid Peroxidase
TRP – Transient Receptor Potential
UAS7 – Urticaria Activity Score
UCT – Urticaria Control Test
WAO – World Allergy Organization
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References
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Kaplan, A. P. and Greaves, M. 2009. Pathogenesis of chronic urticaria. Clin. Exp. Allergy 39: 777–87.
Kern, F. and Lichtenstein, L. M. 1976. Defective histamine release in chronic urticaria. J. Clin. Invest. 57: 1369–77.
Lapolla, W., Desai, N. and English, J. C. 2012. Clinical utility of testing for autoimmunity in chronic idiopathic
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Magerl, M., Altrichter, S., Borzova, E., Gimenez-Arnau, A., Grattan, C., Lawlor, F. et al. 2016. The definition,
diagnostic testing, and management of chronic inducible urticarias - The EAACI/GA
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Maurer, M., Fluhr, J. W. and Khan, D. A. 2018. How to approach chronic inducible urticaria. J. Allergy Clin. Immunol.
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Metz, M., Vadasz, Z., Kocatürk, E. and Giménez-Arnau, A. M. 2020. Omalizumab updosing in chronic spontaneous
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W. W., Holgate, S. T., Lemanske, R. F. et al. (eds.). Middleton’s Allergy: Principles & Practice, 8th Edition.
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Wang, J. and Sampson. H. A. 2011. Food allergy. J. Clin. Invest. Mar; 121(3): 827–35.
Ying, S., Kikuchi, Y., Meng, Q., Kay, A. B. and Kaplan A. P. 2002. TH1/TH2 cytokines and inflammatory cells in
skin biopsy specimens from patients with chronic idiopathic urticaria: comparison with the allergen-induced
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Chapter 6
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Allergic Contact Dermatitis and
Atopic Dermatitis
Luz Fonacier,* Hope Jin, Jake Rosenblum and Sonam Sani
Basics of Patch Testing
PT is the gold standard procedure for diagnosing ACD and identifying the contact allergen
responsible for dermatitis. PT involves applying allergens to the patient’s back for 48 hours in order
to determine if the patient develops a reaction. The use of PT in various clinical scenarios will be
discussed. There is much to be learned regarding the epidemiology and pathophysiology of CD;
however, this chapter will focus on the procedural aspect of CD, which is the patch test. Indications,
protocols, special populations and pearls for PT will be reviewed as well.
Introduction
Overview of Allergic Contact Dermatitis
Contact dermatitis is an inflammatory skin disorder that is characterized by erythema, edema,
vesicles, hyperkeratosis and fissuring. Patients may present with complaints of associated pain,
itch and swelling. Such clinical manifestations vary depending on the chronicity of dermatitis,
as the condition may be acute, subacute or chronic. CD is caused by exposure to an allergen or
irritant, leading to ACD and ICD, respectively. ICD accounts for approximately 80% of all
occupational dermatitis, whereas ACD is less common (Litchman et al. 2022). ICD is a localized,
non-immunologic inflammatory response to a substance that results in direct cellular cytotoxicity;
while ACD, in contrast, is classified as type IV cell-mediated delayed hypersensitivity reaction in
which prior sensitization to an allergen is needed in order to elicit a reaction upon re-exposure to the
allergen (Bolognia 2022). CD is the most common cause of occupational dermatitis and represents
a significant amount of physical and psychosocial burden (Nicholson et al. 2010).
Indications for Patch Testing
PT should be considered in patients with acute or chronic eczematous dermatitis with features
including erythema, edema, weeping, crusting, scaling or lichenification (Johansen et al. 2015).
Avoidance of suspected allergens may lead to improvement in dermatitis; however, identification
of the specific allergen can increase options available to patients and lead to improved outcomes
NYU Langone, Mineola NY, USA.
* Corresponding author: luz.fonacier@nyulangone.org
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(Fonacier and Noor 2018). Thorough histories should be elicited from each patient in order to
determine occupational, environmental and other potential exposures to allergens. Patients with
dermatitis and significant exposures should be considered for patch testing. Other indications
are patients with dermatitis in generalized or regional areas of interest, such as the face, neck,
hands, periumbilical area, and feet and those with dermatitis recalcitrant to conventional therapies
(i.e., topical corticosteroids (TCS) and topical non-steroidal immunomodulatory treatments).
Consider PT in AD patients who have dermatitis that worsens, changes distribution, fails to
improve or immediately rebounds. Other AD considerations that should invoke consideration
of PT are atypical distribution, such as head predominance, hand or foot, eyelid predominance,
cheilitis/perioral predominance, therapy-resistant hand eczema, adult- or adolescent-onset
AD without childhood eczema or severe/widespread dermatitis prior to initiating systemic
immunosuppressant or biologics. Thus, the indications for PT are broad and should be considered
in patients with localized or diffuse, acute, subacute or chronic, pruritic, eczematous, vesicular or
lichenified dermatitis where the clinician has a strong suspicion of ACD.
Special Populations
Children
Children are a particular demographic of interest as one can develop ACD at any age. As with any
patient, a thorough history is important and should be tailored to the patient’s age (diapers and baby
powders in younger children vs. hobbies/sports in older children). Children with persistent AD that
worsens despite standard therapy and late-onset AD are candidates for PT. Children with comorbid
AD may be sensitized to allergens, such as cocamide DEA, lanolin and TCS found in many eczema
treatments (Neale et al. 2021). PT remains the gold standard for diagnosing ACD in children and is
a safe procedure for pediatric patients. Currently, there is no FDA-approved PT device for children
under the age of 6. However, it has been suggested that in children younger than age 6, if PT is at
all needed based on clinical history, certain allergens be diluted to avoid irritation and false positive
reactions (Fisher et al. 2019; Jacob et al. 2017). Table 1 lists a recommended limited panel for patch
testing in children 6–12 years of age. The limited surface area in pediatric patients translates to a
greater emphasis on considering relevance prior to proceeding with PT. Additionally, providers can
consider using the thigh or abdominal area to increase the available surface area for PT (Tam and Yu
2020). In general, children over the age of 12 can be tested similarly to adults.
Table 1. Patch test recommendations for children 6–12 years of age (Jacob et al. 2008).
Primary Allergens Secondary Allergens
1 Bacitracin 11 Fragrance mix 1 1 Black rubber mix
2 Budesonide 12 Fragrance mix 2 2 Dialkyl thioureas
3 Carba mix 13 Lanolin alcohol 3 Mercaptobenzothiazole
4 Cobalt chloride 14 MCI/MI 4 Para-phenylenediamine
5 Cocamidopropyl betaine 15 Myroxylon pereirae (Balsam
6 Colophonium 16 Neomycin sulfate
7 Compositae mix/dandelion
extract
8 Disperse blue 18 Potassium dichromate
9 Ethylenediamine 19 Quaternium 15
10 Formaldehyde 20 Tixocortol-1-pivalate
Jacob, S. E., Brod, B. and Crawford, G. H. 2008. Clinically relevant patch test reactions in children—the United
States-based study. Pediatr. Dermatol. 2008 Sep.–Oct.; 25(5): 520–7.*
of Peru)
17 Nickel sulfate
5 p-tert Butylphenol
formaldehyde resin
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Pregnancy
While there is no absolute contraindication to PT in pregnancy and breastfeeding, postponing PT
until after delivery or completion of breastfeeding is advised (Ingber 2014). However, bothersome
symptoms may be, PT is never an emergency and can always wait for more optimal PT conditions.
Biomedical Devices: Metal and Cement Allergy
Metal is a common allergic sensitizer, and nickel is consistently found to be the most common cause
of ACD worldwide. Hypersensitivity reactions to implanted prosthetic devices are possible and can
have varied presentations including implant failure. More common causes of implant malfunction,
such as mechanical failure and infection should always be ruled out prior. Currently, there is a lack
of evidence to support the risk-stratification of patients for hypersensitivity to cement or metals.
Moreover, there is data to suggest that individuals who have undergone joint implantations have
a higher frequency of positive patch tests compared to the general population; yet the connection
of positive sensitization to clinical outcome remains unknown (Granchi et al. 2008). Therefore,
pre-operative PT is not recommended in those without a history concerning metal, bone cement or
adhesive hypersensitivity. Post-implantation PT can be considered in those with dermatitis/rash near
the site of prosthetic implantation or after implant failure when more likely etiologies have been
ruled out (Pacheco 2019).
Limitations of Patch Testing
Contraindications to Patch Testing
PT is not appropriate in the setting of active generalized exanthematous or erythrodermic eruptions
until the underlying dermatitis is controlled. In addition, it is prudent to rule out other potential
causes of acute generalized presentations, such as drug eruption or mycosis fungoides. As PT is
performed on the patient’s back, it is important to be able to discern positive results from background
skin changes, including extensive tattoos. Patients, with widely prevalent dermatitis or substantial
eczema, compromising the surface area of the back are not good candidates for PT and should first
obtain control of their dermatitis. Similarly, patients with significant actinic damage or sunburn
on the back may not be ideal candidates for PT. Patients with substantial thick, dark hair on the
back need non-irritating hair removal performed 1–2 days prior to the test. PT requires multiple
follow-up visits in a specific time frame, thus patients need to work these visits into their schedule.
Also, excessive sweating and physical activity must be avoided while the patches are on to prevent
dislodging them.
Immunosuppressant agents (such as systemic corticosteroids, cyclosporine or other
immunosuppressive agents) can interfere with PT results. Studies have shown that doses of
prednisone less than 20 mg per day and low doses of cyclosporine (2–3 mg/kg/day) may still yield
clinically relevant PT results (Anveden et al. 2004). It is recommended to avoid the application of
TCS and topical calcineurin inhibitors to the PT site for 5–7 days before testing (Prens et al. 1989).
In addition, patients should avoid excessive sun exposure 2–4 weeks before the application of a
patch test, as ultraviolet radiation can reduce the allergic response (Damian and Halliday 2002).
Special Precautions/Complications of PT
PT is considered to be a generally safe procedure; however, in rare instances, it can be associated
with complications. Most adverse effects are due to testing errors, such as using irritant products,
too high a concentration of test substance and/or leaving the PT panels on for a prolonged period
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(Fisher et al. 2019). Active sensitization, although rare, has been reported (Jensen et al. 2006).
Irritant reactions to adhesive tapes are common and tend to resolve quickly. Other complications
include a flare of existing dermatitis, as well as hypopigmentation and hyperpigmentation of the
skin. Although exceedingly rare, case reports of anaphylactic reactions have been reported after
testing with topical antibiotics, nitrogen mustard and latex (Schmidlin et al. 2020).
Utility and Patch Test Methodology
Allergen Sources
There are several PT panels available, including standard panels as well as expanded series. The
T.R.U.E. (Thin-layer Rapid Use Epicutaneous) Test® is approved for ages 6 and above and consists
of 35 allergens and one negative control preloaded onto chambers. The T.R.U.E. Test® is currently
the only FDA-approved PT panel in the United States. While it is easy to apply, its limitation is in
the preloaded allergens and so testing cannot be individualized for specific patients. A particular
study concluded that 30–40% of causative allergens may be missed with the use of the T.R.U.E.
Test® as compared to the use of the North American Contact Dermatitis Group (NACDG) panel
described below (DeKoven et al. 2021).
Chamber testing is the alternative to T.R.U.E. Test® and can be done with any number of
allergens. The NACDG series consists of 65–80 allergens that are individually loaded into testing
chambers. This gives physicians flexibility and the ability to tailor PT to individual patients,
potentially adding allergens (such as a metals series) from an extended series if thought to be
relevant.
Process of PT
PT is prepared by placing allergens into chambers that can be round or square, mounted on rectangular
strips of adhesive in two rows of five chambers each (10 total) per strip of adhesive. Loading
chambers come in various sizes, depths and materials. Square chambers and round chambers
are comparable, and no chamber is known to be superior to others (Schmidlin et al. 2020). Most
allergens are dispersed in a standard concentration petrolatum solution syringe; a small minority are
delivered in liquid vehicles packaged in either syringes or dropper bottles (Fisher et al. 2019). The
majority of PT allergens should be stored in the refrigerator to maintain the stability of the allergen.
Loading the Chambers
Petrolatum-based allergens are loaded directly into the chamber. The ideal volume is 20 microliters,
meaning just greater than 50% of the chamber should be filled with an allergen (Fisher et al. 2019). In
an 8 mm Finn chamber, it is about a ribbon of the commercially available standardized allergen
from rim to rim. For allergens in liquid form, one drop of mixture is placed into the chamber and is
usually sufficient to saturate the chamber (Figure 1). Using a patients own products can optimize
the diagnosis of ACD, especially in facial, eyelid and lip dermatitis. Personal products can be placed
into individual chambers in suggested concentrations as described in Table 2. PT chambers should
ideally be loaded at the time they are applied. Substances in aqueous vehicles should be loaded into
chambers as close to the application as possible to prevent drying (Joy et al. 2013). Most allergens
in petrolatum vehicles may be prepared 24 to 48 hours before the application if desired. Exceptions
include acrylates and fragrances, which should not be preloaded and should be prepared at the time
of the visit and applied to the skin immediately.
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