Approach to rash in infants and children — viva

Opening (candidate frames the problem)

Examiner: A 14-month-old, 12 hours of fever, irritable, rash over the lower limbs. Talk me through your assessment. [1]

Model answer: I assess sick-or-well first. I take the paediatric assessment triangle and vital signs, because an unwell child with a rash is an emergency regardless of the rash itself. I fully undress the child, examine the whole skin including mucosae, palms and soles, and palpate the lesions - specifically testing blanching with a glass slide. [1]

Examiner (probe): Why blanching first? [7]

Model answer: Because blanching is the single highest-yield bedside test. Erythema and wheals blanch because they are vascular; purpura does not, because the blood is outside the vessel. A non-blanching purpura in an unwell febrile child is meningococcaemia until proven otherwise. [7]

Branch A: the rash does not blanch and the child is unwell

Examiner: The lesions do not blanch. The child is drowsy and tachycardic. What now? [7]

Model answer: I treat this as presumed meningococcaemia. ABCDE: oxygen, IV or IO access, blood cultures and meningococcal PCR, and an immediate parenteral third-generation cephalosporin per local paediatric sepsis protocol, without waiting for the rash to evolve. I manage shock with fluids, reassess after every intervention, involve senior paediatric staff and retrieval, and admit. [7]

Examiner (corner): A senior suggests waiting for the rash to "look typical" before antibiotics. How do you respond? [7]

Model answer: I would not wait. Early meningococcaemia can be nonspecific, and treatment is time-critical; the priority is speed, not diagnostic certainty. I escalate the concern and document the decision. [7]

Branch B: the rash is palpable purpura on the lower limbs and buttocks, child is well

Examiner: The child is alert and well, but the purpura is palpable and there is colicky abdominal pain. [12]

Model answer: This is IgA vasculitis (Henoch-Schonlein purpura): palpable non-blanching purpura on the lower limbs and buttocks with abdominal pain, arthritis and potential renal involvement. I confirm the child is well (purpura in a well child is less often sepsis), check blood pressure and urinalysis for renal involvement, arrange a full blood count and coagulation profile, and monitor for abdominal and renal complications. [12]

Examiner (corner): How do you exclude sepsis in a purpuric child? [7]

Model answer: I cannot fully exclude it at one point in time - "well" is a clinical judgement. Any deterioration, fever or evolving purpura reopens the sepsis question, and I safety-net clearly. [7]

Branch C: widespread blistering and skin tenderness

Examiner: Suppose instead the child has widespread tender erythema, flaccid blisters and peeling, with a positive Nikolsky sign. The mucosa is spared. What is your diagnosis and why not Stevens-Johnson syndrome? [10]

Model answer: This is staphylococcal scalded skin syndrome. The exfoliative toxin cleaves desmoglein-1 superficially, giving a subcorneal split, flaccid clear blisters, flexural accentuation and mucosal sparing. I would not call it SJS/TEN because SJS/TEN shows full-thickness basal-layer necrosis with prominent mucosal involvement. Both can have a positive Nikolsky sign, so the cleavage plane and the mucosa decide it. Management is fluid and temperature support, aseptic skin care and an anti-staphylococcal antibiotic; for SJS/TEN I would stop the culprit drug and involve ophthalmology and burns or PICU. [9] [10]

Closing (synthesis and safety-net)

Examiner: Summarise the framework for the committee. [1]

Model answer: Assess sick-or-well first, then describe morphology, then map distribution, then fold in age, fever, itch and mucosa. Blanching separates erythema from purpura; a non-blanching purpura in an unwell child is an emergency. I resuscitate and treat the threat, name the diagnosis second, and safety-net every disposition with written red-flag advice. [1]