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Simple Diaper Rash or More? Diagnosis: Perianal Streptococcal Dermatitis (PSD)

Author: 
By Amor Khachemoune, M.D., C.W.S., Eric Ehrsam, M.D., and Faiza Kada, M.D.
This 30-month-old girl presented with itchy, painful erythema on the perianal area. She’d had symptoms for 4 weeks and had already been treated with various antifungal creams and zinc oxide ointments with no significant improvement 
for 1 month.

Patient Presentation
A 30-month-old girl presented with a 4-week duration of an itchy, painful erythema on the perianal area (see photo).

The symptoms were worse during defecation. The patient’s mother reported that the girl had been treated for a perianal infection with various antifungal creams and zinc oxide ointments with no significant improvement for the last month. The patient’s parents and siblings were asymptomatic.

On physical examination the perianal erythema had well-defined margins. The area was hot and tender to touch, and a thin mucoid exudate was present.
Based on the patient’s history and because of the well-demarcated perianal redness, we performed a perianal swab.

What’s Your Diagnosis?
(Read on for an answer and for more details about the condition and this case.)

About This Condition
In the case of our patient, the diagnosis of perianal streptococcal dermatitis was confirmed by a positive rapid streptococcal test, and positive cultures for group A beta-hemolytic streptococcus (GABHS) from the perianal swabs. No other lab abnormalities were found.
PSD is a superficial bacterial infection usually due to GABHS. It primarily occurs in children between 6 months and 10 years of age. PSD is often misdiagnosed as irritant contact dermatitis, candidiasis, seborrheic dermatitis, psoriasis, atopic dermatitis, or pinworm infection, and less frequently as inflammatory bowel diseases or sexual abuse.

Patient Presentation and History
Patients with PSD may present with one or a combination of symptoms such as painful defecation, pruritus, tenesmus, constipation, rectal bleeding and anal discharge. A history of sore throat in the patient or others he has close contact with may help in making the diagnosis. Sore throat may resolve prior to the perianal redness developing.

Thoroughly examine patients with perianal erythema and obtain swab cultures of both the pharynx and perianal and/or perigenital areas. The detection of GABHS in asymptomatic siblings points to the necessity of swabbing not only the symptomatic patient but also asymptomatic family members, especially siblings.
Although uncommon, PSD has also been reported as being caused by Staphylococcus aureus. PSD may trigger psoriasis lesion flare-up in patients with a history of psoriasis especially the guttate form. A streptozyme test (normal < 1:160) and antistrepto-dnase-titer B (normal: < 80 U/ml) may be helpful in confirming the diagnosis of a PSD.

Treatment and Follow-up for This Condition
Systemic antibiotic therapy with penicillin, erythromycin, roxithromycin, azithromycin or amoxicillin is effective. This girl was treated with oral penicillinVK 30 mg/kg for 3 weeks, and the perianal dermatitis completely resolved.

Follow-up is necessary because recurrences are common. Many doctors recommend performing post-treatment perianal and throat swabs as well as a urine analysis to monitor for post-streptococcal acute glomerulonephritis. Other complications related to streptococcal infections include rheumatic fever, and guttate psoriasis.