Atypical Histoid Leprosy With Virchowian Features: A Report of a Histologically Deceptive Case.

Histoid leprosy is an uncommon clinicopathological variant of Hansen's disease, characterized by distinct immunological, clinical, histological, and bacteriological features. It is regarded as an intensified form of multibacillary leprosy, marked by an enhanced cellular and humoral immune response. Clinically, this condition typically presents with well-defined papules and nodules on otherwise normal-appearing skin, frequently located on the face, trunk, and extremities of the body. Histopathologically, it is marked by the proliferation of spindle-shaped histiocytes in a "whirl" or "storiform" pattern, accompanied by a significant presence of bacilli, often organized into "bacillary globi." The importance of this variant lies in its high bacillary load, which makes it a potentially significant source of disease transmission if not diagnosed and treated promptly. This case report details the presentation of a 49-year-old male with a history of Hansen's disease, who presented with widespread eucromic to violaceous papules and nodules across his face, upper extremities, torso, and back. Histopathological examination of a cutaneous biopsy revealed a Virchowian pattern, specifically a diffuse dermal infiltrate of foamy histiocytes with an exceptionally high bacillary load and a notable absence of the typical spindle-shaped histiocytes or storiform pattern usually associated with histoid leprosy. This atypical histological presentation, diverging from classic histoid morphology, underscores the critical importance of accurate diagnosis and appropriate treatment to limit its dissemination and prevent significant sequelae in patients. Through this case, we aim to highlight the histologically deceptive nature of some histoid leprosy presentations, emphasizing the fundamental importance of clinicopathological correlation for the accurate diagnosis of this neglected tropical disease and effective disease control.