Adenolipoma of the nail bed: A unique case mimicking a glomus tumor

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Adenolipomas are rare benign tumours characterised by a unique combination of mature adipose tissue and glandular structures. They primarily occur in subcutaneous tissue, and can involve sites, including the head-and-neck region, trunk, and extremities.^[1] These tumours are typically slow-growing and present as painless, well-circumscribed masses that are often asymptomatic until they reach a size that warrants clinical attention. To the best of our knowledge, no case of an adenolipoma in the nail bed has been reported, till date. Herein, we present a case of an adenolipoma arising in the subungual location in a 41-year-old female.

A 41-year-old female with neurofibromatosis type 1 (NF1) presented with 5 months of worsening pain, localised tenderness and cold hypersensitivity noticed in her right 5^th fingernail. She denied trauma to the area. Physical examination of the right 5^th fingernail showed a small, reddish-purple, subungual lesion with exquisite point tenderness [Figure 1]. Dermatoscopic evaluation revealed a blue–grey background that blanched white with pressure [Figure 2]. Considering the lesion’s location and associated symptoms, the leading diagnosis was a glomus tumour. Surgical excision was performed. A white spherical tumour was visualized, which did not immediately present itself. Only after dissection into the medial sulcus, a small visible pearl of this tumor could be dissected out. The excised tissue was sent for pathological examination, and the histologic sections revealed a small fragment of mature adipose tissue with entrapped eccrine glands, consistent with an adenolipoma [Figure 3]. At 2 weeks post-operation, the patient reported marked improvement, with only intermittent pain and resolution of cold hypersensitivity.

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Figure 1:

A 41-year-old female with a history of neurofibromatosis type 1 who presented with 5 months of worsening pain, localised tenderness and cold hypersensitivity of her right 5^th fingernail. Photograph of the right 5^th fingernail shows a small, reddish-purple, subungual lesion (arrow) with exquisite point-tenderness.

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Figure 2:

Onychoscopy of the right 5^th fingernail shows a blue–grey background (arrow) that blanched white and elicited pain with pressure.

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Figure 3:

Haematoxylin and eosin staining of a 0.2 × 0.2 × 0.1 cm excision of the right 5^th fingernail matrix at × 200 magnification shows small fragments of mature adipose tissue and entrapped eccrine glands (arrows).

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Adenolipomas are rare benign tumours characterised by mature adipose tissue interspersed with glandular elements. Histologically, they are seen as well-circumscribed lobules of adipocytes with entrapped eccrine glands or ducts, without cytologic atypia or significant mitotic activity. Clinically, they present as slow-growing, soft, and painless subcutaneous nodules, most often in the head and neck, trunk or extremities and rarely cause functional impairment or discomfort. In this case, however, the lesion occurred in a highly unusual location, the subungual region of the fifth digit, along with a constellation of symptoms not typically associated with adenolipomas, including tenderness, cold hypersensitivity and pressure-elicited pain. These features closely mimicked those of a glomus tumour, which are commonly found in the extremities, such as the distal phalanges of fingers and toes, and typically localise to the subungual area. Glomus tumours are characterised by a classic triad of symptoms: a prolonged history of discomfort, point tenderness and cold hypersensitivity.^[2] This symptom overlap led to an initial clinical impression of a glomus tumour. In addition, the patient had NF1, for which glomus tumours have recently been recognised as a part of the phenotype^[3]. It was only after histopathological analysis revealed the true diagnosis of an adenolipoma, that we could understand the nature of the lesion.

The painful nature of the adenolipoma in this patient raises important questions. While adenolipomas are generally painless, several factors may have accounted for this atypical presentation of pain. First, the compact anatomy of the nail bed allows little room for expansion; even small lesions may exert pressure on surrounding nerve fibres, provoking pain. Second, although the eccrine components of adenolipomas are typically not symptomatic, their entrapment and possible distortion in a confined and innervated region could lead to sensory discomfort. Third, the patient’s history of NF1 may have played a role, either by enhancing neural sensitivity or contributing to a broader spectrum of peripheral nerve-related pathology that may have altered symptomatology. This report contributes to the limited literature on adenolipomas of the nail bed. It offers valuable insights into the clinical presentation and management of this rare lesion, emphasising its potential to mimic other nail bed tumours. The successful surgical excision and absence of recurrence, support the effectiveness of this treatment approach. Furthermore, this case underscores the importance of routine histopathological analysis to confirm diagnoses postoperatively. Although the initial clinical impression suggested a glomus tumour, the final diagnosis of an adenolipoma was only made after histopathological evaluation. Given its rarity, providers should consider adenolipomas in the differential diagnosis of subungual lesions.