A Challenging Case of Atypical Adult Onset Still's Disease Clinically Mimicking Dermatomyositis with Distinctive Histopathologic Findings

A 23-year-old woman from Bangladesh presented with a 6-week history of spiking fevers, myalgias, arthralgias, pruritic rash, marked granulocytosis and lymphadenopathy. On presentation to the emergency department she had brown lichenified plaques on the upper chest and neck; her back had flagellate-like erythema. Hand exam revealed hyperpigmented papules over the metacarpophalangeal joints without periungual capillary loop dilatation. Labs were notable for: minimally positive ANA (1:40), mild transaminitis (AST 56, ALT 73), as well as elevated aldolase (13.8), LDH (1,368), sedimentation rate (>140), C reactive protein (7.5) and ferritin (10,248). She also had a negative Anti Jo1 antibody, rheumatoid factor, and CK (<20). An extensive infectious workup was negative. CT of the chest/ abdomen showed generalized lymphadenopathy with mild splenomegaly. Punch biopsies from the hands and back revealed multiple necrotic keratinocytes mainly in the upper epidermis and within parakeratotic stratum corneum, infiltration of lymphocytes and neutrophils in the papillary and mid dermis and numerous intradermal eosinophils without evidence of vasculitis. In the setting of meeting original Yamaguchi criteria for Adult Onset Still’s Disease (AOSD), negative infectious workup, constellation of lab and imaging findings and characteristic histopathologic findings, the patient was diagnosed with atypical AOSD. She was treated with systemic steroids and had resolution of her symptoms. Atypical presentations of AOSD clinically mimicking dermatomyositis show a distinguishing pattern on histology: dyskeratotic and necrotic keratinocytes in the upper layers of the epidermis, inflammatory infiltrate in the upper and mid dermis, and no evidence of vasculitis, as seen in this patient.