Perianal streptococcal disease

Bright, moist, sharply demarcated perianal erythema with a well-defined edge, often with superficial erosions and anal fissures.

The defining feature of this condition is erythema, and erythema is the sign that brown and black skin hides best - which is very likely part of why this diagnosis is missed and delayed. Do not wait to see bright redness. Rely instead on what pigment does not conceal: the sharply demarcated border, which is a change in texture and sheen as much as in colour and can often be seen with good oblique lighting or felt as a subtle step; the moist, macerated quality of the skin; the fissures and erosions; and the discharge. NICE NG240 makes the general point that rashes can be hard to detect on brown, black or tanned skin, and asks you to check all over the body and to look for petechiae in the conjunctivae; examining in good oblique light is this page's own practical advice, not NG240's. Take the history seriously as the primary evidence - painful defecation, stool withholding and blood-streaked stools in a young child should prompt a swab regardless of how red the skin looks.

• A sharply demarcated perianal border - the edge is the sign, not the colour
• In the defining series: perianal dermatitis in 90%, perianal itching in 78%, rectal pain in 52% and blood-streaked stools in 35%
• Painful defecation and consequent stool withholding and constipation - often the presenting complaint rather than the rash
• Signs of cellulitis were absent in all 31 patients in that series, which is why the authors argued the name should not be 'perianal cellulitis'
• Group A streptococcus in the pharynx in 64%, with the same T type as the perianal isolate
• Intrafamily spread occurred to siblings in half of the situations where it was possible

• Cutaneous candidiasis — Also moist, sharply bordered and perianal, but with satellite lesions and typically in nappy-wearing infants - and it is the treatment this condition usually receives first and fruitlessly
• Nappy rash, candida, and patterns that should worry you — Irritant nappy rash spares the skin folds; this does not, and it occurs in children well past nappies
• Psoriasis, including guttate — Flexural and napkin psoriasis is also sharply demarcated, but with lesions elsewhere, a family history and no response to antibiotics
• Atopic eczema and infected eczema — Also itchy and excoriated, but ill-defined, and perianal skin is an unusual site for isolated eczema
• Impetigo — The same organism group and also superficially eroded and crusted, but not confined to a sharply bordered perianal area
• Scarlet fever — The same organism. A child with perianal streptococcal disease may have streptococcal pharyngitis too - look at the throat

1. Look. This diagnosis is missed because nobody examines the perianal skin of a child who presents with constipation, painful stools or 'thrush that will not clear'
2. Swab the perianal skin for bacterial culture. That is what makes the diagnosis definitive. Examine and consider swabbing the throat as well, since pharyngeal carriage was present in roughly two-thirds
3. Treat with an oral antibiotic active against group A streptococcus, following your local antimicrobial guideline for dose and duration, with topical antiseptic or topical antibiotic as an adjunct
4. Warn about relapse explicitly: it occurred in 39% in the defining series. A child who returns with the same complaint has probably relapsed rather than been misdiagnosed, and needs re-swabbing rather than a different diagnosis
5. Ask about siblings - intrafamily spread to siblings occurred in half of the situations where it could
6. Treat the constipation and stool withholding that the pain has caused; clearing the infection alone does not undo a withholding habit
7. Keep the safeguarding question open and separate. Finding a cause does not discharge the duty to consider the others

Discharge on oral antibiotics with GP follow-up and a swab result to chase. Admission is almost never needed and systemic illness suggests a different diagnosis.

• Kokx NP, Comstock JA, Facklam RR. Streptococcal perianal disease in children. Pediatrics 1987;80(5):659-63 - 31 children; symptom frequencies, 39% relapse, absence of cellulitis
• Pennycook KM, McCready TA. Perianal streptococcal dermatitis. StatPearls, 2023 - age range and diagnostic approach
• NICE NG240 - Meningitis (bacterial) and meningococcal disease: recognition, diagnosis and management. Recommendation 1.1.12: check all over the body (including nappy areas), check for petechiae in the conjunctivae, and note that rashes can be hard to detect on brown, black or tanned skin