The Diagnosis: Crusted Scabies
Approximately 1 year prior to presentation the patient completed a course of therapy comprised of repeat doses of ivermectin and permethrin for crusted scabies. He stated that the crusts had recurred shortly after treatment (Figure 1). The initial differential diagnosis included crusted scabies, pityriasis rubra pilaris, and psoriasis. Scraping from the interdigital web space (Figure 2) revealed multiple scabies mites, scabella, and ova (Figure 3). The patient was diagnosed with crusted scabies. Laboratory test results revealed a normal white blood cell count of 7300/μL, with an elevated eosinophil count of 1900/μL (reference range, <500/μL). Human T-lymphotropic virus 1 (HTLV-1) was found to be positive. Serum protein electrophoresis showed a moderate polyclonal increase in gamma globulins. Treatment was promptly initiated with permethrin cream 5% applied to the whole body for a total of 2 treatments that were administered 7 days apart. Ivermectin also was started at 200 μg/kg and was given on days 1, 7, 14, and 29. Salicylic acid cream 25% was applied daily to help hasten resolution of the crusts.
 Figure 1. Generalized crusts and hyperkeratotic plaques on both legs. |  Figure 2. Crusts on the dorsal aspect and interdigital web space of the left hand. |
Figure 3. Microscopic examination of scrapings from interdigital crusts showing mites, scabella, and ova.
Human T-lymphotropic virus 1 is endemic to Japan, Central and South America, the Middle East, and regions of Africa and the Caribbean.1 Multiple cases of HTLV-1 associated with crusted scabies have been reported in endemic areas.2-6 In the present case, we encountered a patient with crusted scabies and HTLV-1 in a nonendemic area.
Cases of HTLV-1 and crusted scabies have been reported in Brazil, Peru, and Central Australia.3,4,7 A retrospective study in Brazil showed a notable association between HTLV-1 infection and crusted scabies; of 23 patients with crusted scabies, 21 were HTLV-1 positive.3 In another small study from Peru, 23 patients with crusted scabies were tested for HTLV-1 and 16 (70%) were seropositive.4 Neither study had a control group for comparison; however, interestingly, the estimated seroprevalence in the general population (based on blood donors) is only 0.04% to 1% and 1.2% to 1.7% in Brazil and Peru, respectively, thus reinforcing the association between HTLV-1 and crusted scabies.1 Crusted scabies and HTLV-1 seropositivity acting as a predictor for adult T-cell leukemia/lymphoma (ATL) has been reported8 but not consistently.3 Our patient had abnormal serum protein electrophoresis findings. Although the results were not diagnostic of ATL, patients with HTLV-1 are at increased risk for ATL and the pres-ence of this virus is important to document when there is a high index of suspicion for ATL, as with crusted scabies.
Our patient resided in the northeastern United States and there was no evidence in support of underlying immunosuppression. This case of crusted scabies is unique because the patient was HTLV-1 positive without other underlying immunocompromise and he resided in a region where HTLV-1 is nonendemic. In light of these findings, the present case serves as a reminder to check for HTLV-1 infection in those patients with severe or crusted scabies and without an identifiable reason for immunosuppression, even if the patient resides in an area that is nonendemic for HTLV-1.