LAUSR

An 8-day-old boy born at term via a normal vaginal delivery was admitted with right arm blistering erythema and swelling. The patient was transferred to our emergency department due to worsening arm necrosis. On examination, the right arm was edematous, erythematous with black discoloration and desquamation (Fig. 1). These findings were sharply demarcated and extended to involve the hand and fingers. The growth parameters were within the normal limits. The neonate did not appear to be in distress but had an absent grasp reflex in the affected arm. There was no history of cord compression or traction, prenatal complications, or medication use. Duplex ultrasound revealed patent subclavian, brachial, radial, and ulnar arteries, bilaterally. Magnetic resonance imaging showed massive edema involving the subcutaneous tissues and muscles extending from the proximal arm near the axilla to the hand and fingers. CT angiography of the upper arm revealed patent arteries. Workup for thrombophilia and systemic infections was negative. The patient was treated for extensive myositis, fasciitis, and cellulitis of the right upper extremity. Three sessions of necrotic tissue debridement were done, and tissue culture grew Enterobacter cloacae (MDR) requiring IV antibiotics. On microscopy, a predominantly lobular panniculitis with numerous histiocytes and focal needle-shaped crystal formation was seen (Fig. 2). PAS stain was non-revealing. What is your diagnosis?