Recalcitrant rash in a 7-month-old infant

A 7-month-old boy presents to the allergy, asthma, and immunology clinic with a medical history significant for slow weight gain in the newborn period, recurrent thrush, and a brief hospitalization for a viral respiratory illness at 3 months of age. He was referred from his primary care provider due to concerns of a rash that has not improved despite a variety of treatments. The rash first appeared at approximately 2 months of age, and although it has waxed and waned over the previous 5 months, it never completely resolves. While hospitalized for his respiratory illness at 3 months of age, a scabies prep of the rash was performed, but the result was inconclusive. The rash has been treated with permethrin on 2 separate occasions due to concern for scabies, along with topical corticosteroids for eczema and oral antifungals and antibiotics due to concern for fungal and bacterial infections. Despite these treatments there has been no significant improvement in the rash, and it has continued to spread throughout his inguinal area, trunk, face, and scalp. On physical examination he is a pleasant infant, but throughout the encounter he scratches at the various lesions on his body. His scalp has thick greasy yellow plaques with significant inflammation (Fig 1), and he has reddish-brown lesions on his trunk with severely erythematous areas of denuded skin in his inguinal folds and neck. He has a thick white exudate occluding visualization of his left tympanic membrane. There is an irregularly shaped hard mass measuring approximately 1.5 cm behind his lower 2 front teeth (Fig 2), and white plaques on his gums. Laboratory tests demonstrate normal liver and bone marrow function, no elevation in inflammatory markers, and no evidence of human immunodeficiency virus infection or other immunodeficiency. Radiographs of the skull reveal at least 2 well-defined lucent lesions; the larger lesion measures approximately 1.3 × 1.3 cm and is seen overlying the occipital bone, with a smaller lesion in the anterior lambdoid suture (Fig 3). A follow-up osseous survey demonstrates at least 3 calvarial lesions but does not demonstrate lesions outside the skull (Fig 4). Skin biopsy and genetic testing confirm the diagnosis.