Subungual hyperkeratosis as a diagnostic cue in crusted scabies.

Crusted scabies (previously referred to as Norwegian scabies) is an uncommon, severe form of infestation, characterized by infestation of the skin with an exceedingly high number of scabies mites. Severe complications of crusted scabies include erythroderma, bacteremia, as well as nosocomial transmission . The classic cutaneous findings of marked “wart-like” scale, hyperkeratosis, and nail changes, can support a clinical diagnosis if recognized . Subungual hyperkeratosis is particularly important because the nails may serve as both a diagnostic site for bedside microscopy and a reservoir for ongoing infestation . A 65-year-old man with vascular dementia, schizophrenia, and chronic obstructive pulmonary disease residing at an assisted living facility presented to the emergency department due to a two-month history of progressively worsening, extensive, pruritic rash, along with dyspnea and worsening confusion. He had previously been treated with triamcinolone 0.1% cream without improvement. On presentation, the patient was found to be erythrodermic with diffuse scaling, and scattered excoriations (A). Marked palmar and subungual hyperkeratosis (B–C) prompted immediate mineral oil preparation of a fingernail scraping, which revealed scybala under microscopy (A). Based on this bedside finding, contact precautions and empiric treatment were initiated before histopathology results were available. Treatment consisted of topical permethrin 5% cream applied every other day for fourteen days, and oral ivermectin at a dose of 200 mcg/kg on seven nonconsecutive days: days 1, 2, 8, 9, 15, 22 and 29 . Concomitant MRSA bacteremia and COVID-19 infections were treated with intravenous vancomycin and dexamethasone with remdesivir, respectively. Histopathology of a 4-mm punch biopsy of a forearm subsequently demonstrated a dense neutrophilic crust and numerous scabies mites (B). The patient’s rash and pruritus gradually resolved with treatment over the course of two weeks, and he was discharged to the assisted living facility in stable condition. Crusted scabies. A, Diffuse, exfoliative dermatitis involving trunk and extremities. B, Marked subungual debris and hyperkeratosis with fissuring and scale on hand. C, Marked hyperkeratosis of palmar surface of fingers.