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Case 84: Unhappy Camper
259
•
Lyme arthritis, which usually aects the knees
•
Nervous system eects, including meningitis, facial nerve palsy or other neuropa-
thies with shooting pains
•
Carditis, with abnormal heart rhythms
If still untreated or inadequately treated, this can develop into late persistent Lyme disease with
destructive lesions and chronic, severe symptoms.
Treatment is with antibiotics, the type and duration depending on the age of the patient,
presentation and severity of the disease. The antibiotics commonly used are doxycycline,
amoxicillin and ceftriaxone.
Exposure to infectious agents is prevented by avoiding tick bites and wearing long socks,
trousers, and long sleeves; using insect repellents; and quickly removing ticks before they are
able to transmit infection. Vaccination is not available.
KEY POINTS
•
Lyme disea se is the most com mon tick-borne in fection in the N orthern He misphere,
caused by the spirochete B. burgdorferi.
•
Clinical and epidemiologic criteria are often enough to make a diagnosis if typical.
Early Lyme disease most commonly presents with flu-like symptoms and erythema
migrans.
•
Serology is the laboratory test of choice, but repeat tests may be needed if done
too early in the infection, and confirmation of positive tests is needed to exclude
false-positive reactions.
•
Prevention of Lyme disease requires public awareness of avoiding tick bites and
early tick removal.
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CASE 85: DIARRHOEA IN AN ELDERLY MAN
An 80-year-old man living in a care home presents to the emergency department with a
4-day history of cramping abdominal pain and watery, non-bloody diarrhoea. He denies
vomiting and states his diarrhoea has been worsening, with five episodes of loose stool in the
past 24 hours. All of his meals are provided by the care home. No other care home residents
are symptomatic. He has no recent travel history.
He is being treated for a catheter-associated urinary tract infection with co-amoxiclav by his
GP. He had colon cancer, for which he had a partial colectomy 1 year ago. His medication
includes aspirin and a proton pump inhibitor.
Examination
Temperature 38.1°C, oxygen saturation 95%, respiratory rate 18, pulse 112, blood pressure
100/65 m m H g.
He has signs of mild dehydration. His abdomen is mildly distended and tender, but there are
no signs of guarding or rebound tenderness. Bowel sounds are active. There is no organo-
megaly. His urinary catheter is draining straw-coloured urine. Rectal examination reveals a
large prostate and diarrhoeal stool with no evidence of blood.
INVESTIGATIONS
Bloods
Reference values
Haemoglobin 11.4 g/dL 11.4–15.0 g/dL
White cell count
28.5 × 10
9
/L
3.9–10.6 g/dL
Platelets
342 × 10
9
/L 150–440 × 10
9
/L
C-reactive protein 86 mg/L <5 mg/L
Radiology
Abdominal radiograph shows dilated and thickened loops of bowel suggestive of colitis.
Microbiology
Blood cultures were negative.
Stool was sent for testing but no results are available yet.
QUESTIONS
1. What is his most likely cause, and what is the differential diagnosis of watery
diarrhoea?
2. What tests would you request on the stool sample?
3. What is the appropriate treatment?
DOI: 10.1201/9781003242697-89
261
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100 Cases in Clinical Pathology and Laboratory Medicine
262
ANSWERS
The most likely cause of this elderly gentleman’s watery, non-bloody diarrhoea is Clostridium
dicile bacterial gastroenteritis, given the very high peripheral white cell count and raised
inflammatory markers (CRP) associated with the following risk factors: recent hospital
admission, living in a care home, antibiotic therapy, bowel surgery and being on proton
pump inhibitors. Important negative features of the history include no travel, not eating out
and no illness in other care home residents.
C. dicile is an anaerobic, spore-forming bacterium that is carried in the gut of some people.
It causes disease (pseudomembranous colitis) through production of toxins that damage the
colonic mucosa. In severe disease it can lead to toxic megacolon, bowel perforation and death.
The dierential diagnosis of watery diarrhoea includes:
•
Viral—Enterovirus, rotavirus (usually in children), and norovirus (in which vomit-
ing is almost always present)
•
Bacterial—Campylobacter spp., C. dicile, Yersinia enterocolitica, Salmonella sp., Shigella sp.
(usually bloody diarrhoea), Vibrio cholera (associated with contact or travel to endemic
areas)
•
Parasitic—Giardia lamblia (appropriate travel history required) or cryptosporidium in
the immunocompromised or young children
•
Toxi ns (which have the shortest incubation period after exposure)—Staphylococcal
food poisoning, Bacillus cereus toxin or enterotoxogenic Escherichia coli
•
Non-infectious causes—Alcohol excess, lactose intolerance or inflammatory bowel
disease
Investigations of watery diarrhoea must include a stool sample sent for:
•
Microscopy and culture and sensitivity (MC&S) for bacterial causes
•
Polymerase chain reaction (PCR) testing looking for viral causes
•
Ova, cysts and parasites
•
C. dicile toxin testing, as only toxin-producing strains cause disease. Culture meth-
ods for C. dicile are slow and no longer used for diagnosis
Blood cultures are taken to exclude urinary sepsis and Gram-negative sepsis. The latter could
indicate a perforation of the gut or leakage of bowel contents that would indicate severe
colonic disease.
Treatment is centred on removing risk factors as possible and treating with antibiotics (met-
ronidazole or vancyomycin). Choice of antibiotics depends on the severity of the disease and
local hospital policy. In severe or life-threatening cases, surgical management may also be
required (colectomy). In chronic or recurrent cases, alternative therapy includes probiotics,
faecal enemas and fidaxomicin.
Prevention is by eliminating risk factors, thereby reducing the likelihood of developing dis-
ease. Reduced transmission from person to person requires hand washing with soap and
water after every contact with a patient having diarrhoea. Alcohol hand rub does not destroy
the spores and is therefore not sucient to prevent spread. All patients with C. dicile should
be isolated because its spores are hardy and easily contaminate the environment. This is why
environmental cleaning plays an important role in controlling outbreaks.
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Case 85: Diarrhoea in an Elderly Man
263
KEY POINTS
•
Risk factors for C. difficile infection include being elderly, recent hospital admis-
sion, living in a care home, antibiotics, bowel surgery, laxatives, proton pump
inhibitors and immune suppression.
•
A stool sample must be sent for C. difficile toxin testing if suspected, even if the
patient is not in hospital.
•
Reduced transmission from person to person requires hand washing with soap
and water and good environmental cleaning.
•
Treatment is with an antibiotic (metronidazole or vancomycin) depending on
severity of disease and local hospital policy. Removing risk factors is an important
part of controlling infection.
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CASE 86: A PAINFUL KNEE
A 46-year-old male presents to the emergency department complaining of a painful, swol-
len right knee. He has been complaining of pains in his knee for months and underwent an
arthroscopy 3 weeks ago for a degenerative meniscus. He has not had any other surgery to
the knee, has no prosthetic joint, and does not remember any significant trauma. He is gener-
ally fit and healthy, and he plays tennis regularly. He has no other significant medical history.
He is married and living with his wife. He denies any extramarital relations and has no history of
any urethral discharge or genital ulcers. He works as a teacher and has no recent travel history.
Examination
On examination, he has an erythematous, swollen right knee. He has diculty weight-bear-
ing on the right leg. He had a reduced range of movement in the aected knee. His tempera-
ture was 37.5°C, blood pressure 130/80 and heart rate 90 beats/min.
INVESTIGATIONS
Bloods
Haemoglobin 13.8 g/dL
White cell count
13.0 × 10
9
/L
Platelets
298 × 10
9
/L
C-reactive protein 240 mg/L
Radiology
A plain radiograph of the knee shows a soft tissue swelling, but no evidence of
osteomyelitis is noted.
QUESTIONS
1. What is your differential diagnosis for acute monoarthritis?
2. What further investigations would you like to perform on this patient?
3. How would you manage this patient?
DOI: 10.1201/9781003242697-90
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100 Cases in Clinical Pathology and Laboratory Medicine
266
ANSWERS
The dierential diagnosis of a unilateral swollen knee/monoarthritis includes:
1. Septic arthritis
2. Crystal-induced arthritis
a. Gout—Uric acid crystals
b. Pseudogout—Calcium pyrophosphate crystals
c. Other—Calcium oxalate
3. Osteoarthritis
4. Reactive arthritis (autoimmune). Reaction to infection in another part of the body,
e.g., Reiter’s syndrome. Usually more than a single large joint is involved
5. Traumatic arthritis
6. Haemarthrosis—Bleeding into the knee. Occurs with minor trauma in
haemophiliacs
Examination of the joint fluid is often required to aid the diagnosis. The gold standard for
diagnosis of septic arthritis is joint aspiration to identify an organism. In some instances
this may be dicult, and image-guided aspiration is recommended. The samples should be
sent for microscopy, culture, and sensitivity; tuberculosis (TB) culture (if clinically indicated)
and molecular testing ( polymerase chain reaction [PCR]) if the patient has already started
antibiotics. The microscopy will give an initial result of the cell count and a Gram stain. The
cell count will identify whether white blood cells (indicating inflammation or infection) or red
blood cells (indicating haemarthrosis) are present. The Gram stain may identify organisms
present in the fluid. Polarised light microscopy is required to look for crystals. Microscopy
is fairly quick and cheap. However, it is not very sensitive in identifying the pathogen (50%
sensitivity). These initial results could guide empiric therapy while waiting for culture results
for a more targeted therapy. In instances where antibiotics are given prior to the aspiration,
organisms may be seen but will not grow on the culture media. When this occurs, molecular
tests (e.g., 16s PCR) could help identify the organism.
In this patient, aspiration was performed, and the microscopy showed a high white blood
cell count and Gram-positive cocci in clusters and chains. Culture results the next day grew
Staphylococcus aureus. Microscopy for crystals was negative.
Septic arthritis is an infection of the joint space and is most often monoarticular. It carries
significant morbidity to the patient and could lead to destruction of the infected joint. It can
also extend into the bone, leading to osteomyelitis. Septic arthritis is most commonly due to
bacterial infection, but may occasionally be caused by mycobacteria, fungi or viruses.
There are many predisposing factors for septic arthritis, and these include age, prosthetic
joints, diabetes mellitus, underlying arthritis and recent procedures to the aected joint.
The most common route of infection is haematogenous spread; however, direct inoculation
of bacteria to the joint following procedures or trauma is also common. Septic arthritis is
caused by many pathogens, the most common of which is S. aureus, followed by streptococci.
In sexually active young adults, it is important to consider gonococcal arthritis caused by
Neisseria gonorrhoeae. The usual presentation is that of a painful, warm, red and swollen joint,
the most common site being the knee.
Treatment of septic arthritis requires appropriate surgical drainage and antibiotic therapy.
Treatment with antibiotics is usually for a prolonged period. Patients are usually kept for a
minimum of 2 weeks of parenteral antibiotics that are then switched to an oral option for a
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Case 86: A Painful Knee
267
further 2 weeks. The duration will vary depending on the pathogen isolated and response to
treatment.
Radiography is usually normal on admission. However, it must always be done to monitor
changes and to have a point of comparison. Surgical drainage and washout also form part of
the management to reduce the burden of infection in the joint.
KEY POINTS
•
Septic arthritis is an infection of a joint, usually caused by S. aureus and usually
monoarticular.
•
Joint aspiration is the gold standard diagnostic tool for septic arthritis and identi-
fying other causes of acute monoarthritis.
•
Predisposing factors for septic arthritis include age, prosthetic joints, diabetes
mellitus, underlying arthritis and recent procedures to the affected joint.
•
The most common route of infection is haematogenous spread.
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