DP22 A solitary neurofibroma masquerading as smooth muscle hamartoma: a clinicopathological challenge

Abstract Neurofibroma is a benign tumour of the peripheral nerve sheath, typically presenting as soft to firm papules or nodules. While the classic presentation is well documented, unusual clinical variants can pose a diagnostic challenge. Here, we report a rare case of a solitary neurofibroma presenting as a well-defined, indurated brownish plaque with follicular papules, clinically mimicking smooth muscle hamartoma and follicular mucinosis. A 23-year-old woman presented with a solitary, brownish, elevated lesion on her upper back persisting for 10 years, with a gradual increase in size over the past 2–3 years. The lesion caused mild discomfort upon deep palpation, without any discharge or associated systemic symptoms. Cutaneous examination revealed a well-demarcated, indurated brownish plaque with follicular papules on the left upper back. Darier sign was negative, and systemic examination was unremarkable. Histopathological examination of the lesion showed a thinned-out epidermis with spindle cell proliferation exhibiting bland chromatin and wavy ends, positive for S100. Enhanced dermal mucin deposition was highlighted with alcian blue–periodic acid–Schiff staining, with enlarged nerve trunks and myxoid changes in the lower dermis, confirming the diagnosis of neuro­fibroma. The clinical differential diagnoses included smooth muscle hamartoma and follicular mucinosis. Smooth muscle hamartoma typically presents with hyperpigmentation and hypertrichosis, while follicular mucinosis is characterized by folliculocentric mucin deposition and lymphocytic infiltrates. In our case, the patient presented with an indurated plaque, and histopathological examination confirmed the diagnosis of neurofibroma, which posed a unique clinical challenge. Histopathological confirmation played a crucial role in establishing the definitive diagnosis of neurofibroma. This case highlights the importance of considering neurofibroma in atypical dermatological presentations and underscores the necessity of histological evaluation for accurate diagnosis. This case broadens the clinical spectrum of neurofibroma, emphasizing the need for histopathological confirmation in lesions with an unusual presentation. Early and accurate diagnosis is essential to differentiate neurofibroma from other dermatological conditions and to ensure appropriate patient management.