Background: Leprosy is a chronic infection caused by Mycobacterium leprae and Mycobacterium lepromatosis with protean mucocutaneous manifestations. Commonly, its clinical expression consists of, inter alia, macules, papules, plaques, nodules, or diffusely infiltrated skin. A rare and highly infectious variant, histoid leprosy, can be suspected in a leprosy patient undergoing treatment, if they present with new nodules, strange plaques, or papules. In de novo histoid leprosy, such lesions develop in patients with no prior history of leprosy or therapy. There are increasing cases of histoid leprosy occurring de novo, which, together with its rarity and resemblance to other skin conditions, pose a diagnostic challenge. Clinicopathological correlation is key to arriving at the right diagnosis. We present a case of de novo histoid leprosy clinically simulating xanthoma disseminatum.
Objectives: To describe a case of de novo histoid leprosy and highlight how it differs from xanthoma disseminatum.
Methods: A retrospective descriptive study of a patient with histoid leprosy. Secondary data was obtained from the patient’s file. Pictures and biopsies were taken after obtaining informed consent from the patient and specific laboratory investigations were performed. All ethical requirements were duly complied with.
Results: A 35-year-old male from Malawi with no prior skin lesions or history of leprosy presented with generalised asymptomatic nodules, plaques and tumours involving the skin and the oral mucosa. Clustering and pale-yellow appearance of some of the lesions, and involvement of the oral mucosa were highly suggestive of xanthoma disseminatum. Histoplasmosis and histoid leprosy were included in the differential diagnosis. Histopathology showed epidermal atrophy with effacement of the rete ridges, diffuse dermal proliferation of epithelioid cells, some of which appeared fusiform, and contained abundant foamy cytoplasm. Among the vacuolated histiocytes were scattered lymphocytes. No Touton giant cells were identified. Wade–Fite staining highlighted abundant, bright red, acid-fast bacilli within the histiocytes, confirming histoid leprosy.
Conclusion: Histoid leprosy is a highly infectious rare variant of leprosy which can be suspected in a leprosy patient during treatment. De novo histoid leprosy cases can be overlooked and mistaken for other skin conditions, and a high index of suspicion should be maintained in a patient presenting with shiny nodules, papules, or plaques. Histoid leprosy should be excluded in all patients clinically diagnosed with xanthoma disseminatum, and vice versa.
Author Contributions
Conceptualization, A.R.S.-R. and R.A.M.; methodology, A.R.S.-R. and R.A.M.; software, A.R.S.-R. and R.A.M.; validation, A.R.S.-R.; formal analysis, A.R.S.-R. and R.A.M.; investigation, A.R.S.-R. and R.A.M.; resources, A.R.S.-R. and R.A.M.; data curation, R.A.M.; writing—original draft preparation, A.R.S.-R. and R.A.M.; writing—review and editing, A.R.S.-R.; visualization, A.R.S.-R.; supervision, A.R.S.-R.; project administration, A.R.S.-R. and R.A.M. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
The study was conducted in accordance with South African Ethics in Health Research Guidelines: 2024 Edition, which states that “Current health research ethics guidelines indicate that a single case report (≤3 patients) is usually exempt from research ethics approval” (page 57).
Informed Consent Statement
Written informed consent was obtained from the patient.
Data Availability Statement
The data presented in this study are available from the corresponding author on request.
Conflicts of Interest
The authors declare no conflict of interest.
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