Crusted Scabies Infection in the Setting of Chronic Steroid and Omalizumab Use

Scabies infection is a very common skin disease that occurs due to infestation with the Sarcoptes scabei mite. Typically, it results in intensely pruritic papules and excoriations in the webs of the hand, groin, or axilla, and remains limited in its spread. In rare cases, the disease can become diffuse and progress to crusted or nodular subtypes. Here, we report the case of crusted scabies infestation in a 69-year-old male who presented with a diffuse pruritic, erythematous, and petechial rash. His medical history was significant for severe idiopathic urticaria treated with omalizumab. Before starting omalizumab, the patient was self-medicating for several months with corticosteroids obtained through his veterinary practice to alleviate symptoms. His presentation was complicated by immune thrombocytopenic purpura and muscle weakness, likely secondary to omalizumab and corticosteroid use, respectively. The patient underwent an extensive rheumatologic workup until skin biopsy confirmed the underlying etiology as crusted scabies infestation. He was treated with ivermectin and weekly 5% permethrin skin cream with great improvement of his rash; however, unfortunately, he succumbed to bacterial sepsis. Scabies infestation can masquerade as a manifestation of other systemic diseases and is often misdiagnosed. As this case illustrates, initial misdiagnosis and subsequent treatment with immunosuppressive drug regimens can cause preventable, but potentially fatal, concomitant superinfections.