The culprit? group A strep
Group A beta-hemolytic streptococcus (GABHS) is the culprit with this form of dermatitis. While the condition was once referred to as “perianal cellulitis,” the indolent nature of the infection and the related itching lent support to the more common description of perianal streptococcal dermatitis.
Up to 92% of the cases of perianal streptococcal dermatitis involve positive pharyngeal cultures for GABHS, even in the absence of pharyngeal symptoms.3 This lends support to the theory that auto-inoculation is the cause for perianal or perineal disease.1 Asymptomatic perineal carriage of GABHS is rare in healthy people, but has been found in 6% of children with streptococcal pharyngitis.1
Rarely, group B or G beta-hemolytic streptococcus or Staphylococcus aureus is identified by culture as the cause of disease.
A condition that’s easy to mistake for candidiasis
The differential diagnosis of perianal streptococcal dermatitis includes candidiasis, diaper dermatitis, irritant dermatitis (such as trauma from heavy wiping), atopic dermatitis, allergic contact dermatitis, seborrheic dermatitis, pinworm infection, cellulitis, psoriasis, inflammatory bowel disease, histiocytosis, and sexual abuse. Patients are often initially misdiagnosed and come back to the office when treatment with topical steroids, topical antifungals, or oral regimens for pinworm infection fail.
Suspect perianal streptococcal dermatitis when the patient presents with a well-dermarcated, moist, bright red perianal rash with no satellite lesions. Also, consider this diagnosis when a perianal rash fails to respond to initial treatment as expected.
A rapid strep test or culture of the affected region helps to confirm perianal streptococcal dermatitis caused by GABHS.