Impetigo and bacterial skin infection — formative SAQs

SAQ 1 (10 marks)

A 14-month-old infant is brought to the emergency department with a two-day history of flaccid, translucent bullae on the trunk and neck, several of which have ruptured to leave a thin collarette of scale and a moist base. The infant is febrile to 38.6 degrees Celsius, irritable, and has widespread, tender erythema extending beyond the bullae, with wrinkling of the skin around the neck that shears with gentle wiping. [8]

Question: Outline the diagnosis, immediate management, and the stepwise treatment of this infant, including how you would distinguish this from other blistering disorders. (10 marks) [8]

Model answer

Diagnosis and recognition (2 marks). The most likely diagnosis is staphylococcal scalded skin syndrome, the circulating-toxin extreme of the same exfoliative-toxin mechanism that causes bullous impetigo. The widespread tender erythema, flaccid bullae, sheet-like desquamation with a positive Nikolsky sign, fever and irritability in an infant are characteristic. This is a hospital emergency: admit for intravenous therapy and supportive care. [8]

Immediate management and resuscitation (2 marks). Admit, establish intravenous access, and treat as a burn: start intravenous anti-staphylococcal therapy with flucloxacillin (vancomycin or clindamycin if the child is critical or MRSA is likely), provide meticulous fluid, electrolyte and temperature management, apply non-adherent wound care and adequate analgesia, and monitor for secondary infection and heat and fluid loss. Identify and treat the primary staphylococcal focus, often a conjunctival, umbilical or skin site. [8]

Distinguishing the blistering disorders (2 marks). The decisive features are the spared mucous membranes and the superficial split, which separate staphylococcal scalded skin syndrome from Stevens-Johnson syndrome and toxic epidermal necrolysis (which involve the mucosae and follow a drug exposure) and from toxic shock syndrome. Mucosae are spared because mucosal epithelium co-expresses desmoglein-3, which compensates when desmoglein-1 is cleaved by the exfoliative toxin. A skin biopsy is reserved for the genuinely ambiguous case. [8]

Stepwise treatment of the broader disease (2 marks). For bullous impetigo in a well child, an oral anti-staphylococcal antibiotic such as flucloxacillin for five days is first-line; for the toxin-mediated extreme here, intravenous therapy and burns-style care are required. State the principle: localised toxin gives bullous impetigo, circulating toxin gives staphylococcal scalded skin syndrome, and the severity of the child dictates the setting. [8]

Disposition and safety-netting (2 marks). Admit the infant to a monitored bed, continue supportive care and intravenous therapy, and de-escalate to oral therapy as the child recovers. On discharge, give a clear safety-net for spreading redness, fever, lethargy and poor feeding, and reinforce skin care. The outcome in children is generally good with prompt treatment, in contrast to the high mortality in adults. [8]