Muscular weakness with knuckle erythema

Case history

Over a three-month period, a 14-year-old boy developed a facial rash, pruritic erythematous patches on the back of his knuckles and interphalangeal joints, and periungual erythema with focal haemorrhage (Figure 1). This was accompanied by a general malaise and progressive weakness of his proximal limb muscles. Skin biopsy revealed perivascular lymphocytic inflammation and focal necrosis of basal keratinocytes with vacuolar changes at the epidermal junction (Figure 2).