A Rare Case of Pigmented Bowen Disease of the Nail Fold
Bowen disease (BD), also known as squamous cell carcinoma in situ, is a precancerous condition that can progress to invasive carcinoma if left untreated. Among its variants, pigmented Bowen disease is exceptionally rare, characterized by the presence of increased melanin pigment in the epidermis or papillary dermis, in addition to the typical features of BD. This article presents a detailed account of a rare case of pigmented Bowen disease located on the proximal nail fold, highlighting its clinical presentation, diagnostic process, and management.
The patient, a 29-year-old Chinese woman, presented with a 4-year history of a gradually enlarging brown-black uniformly pigmented patch on the proximal nail fold of the left fourth finger. The lesion measured approximately 2.0 cm by 1.5 cm and exhibited a normal surface texture without any signs of scaling or keratosis. Notably, the patient denied any history of trauma, wart, or tumor in the affected area. Clinical examination revealed no color modification or longitudinal melanonychia on the nail plate, which are often associated with malignant melanoma.
To confirm the diagnosis, a comprehensive immunohistochemical analysis was performed. The results were negative for human papillomavirus (HPV) antigen, carcinoembryonic antigen, HMB45, epithelial membrane antigen, cytokeratin (CK)8/18, and S100. However, immunostains for P53, CK5/6, and some parts of P16 were positive, and Ki-67 (MIB-1) showed a 40% positivity rate. Mycologic examination ruled out fungal infection, further supporting the diagnosis of pigmented Bowen disease.
Histopathologic examination of the excised lesion revealed hyperkeratosis, parakeratosis, dyskeratotic cells, and apoptotic keratinocytes. Irregularly arranged tumor cells with atypical nuclei were also observed, confirming the diagnosis of pigmented Bowen disease. The lesion was completely excised with a 0.3-cm margin around the affected area. The wound healed well, and there was no recurrence over an 11-month follow-up period.
The etiology of pigmented Bowen disease in this case was presumed to be idiopathic, as the patient had no history of sun exposure, arsenic exposure, viral infection, trauma, or radiation. Although high-risk mucosal HPVs are known to play a significant role in the development of BD in the periungual region, this case demonstrated no symptoms or signs of HPV infection. This finding is noteworthy, as HPV is highly detected in digital BD cases.
Pigmented Bowen disease is a rare variant, with only 7 out of 420 BD cases (1.67%) reported to be pigmented in a previous study. The pigmentation in BD is attributed to the increased number of melanocytic hyperplasia by hypertrophic dendritic processes dispersed through the tumor. In well-differentiated stages, atypical keratinocytes develop melanin, leading to pigmentation without scaling or keratosis. However, as the disease progresses, these atypical keratinocytes may result in the loss of pigmentation, keratosis, and scaling.
The differential diagnosis of pigmented Bowen disease includes malignant melanoma, which can be distinguished by the absence of micro-Hutchinson sign, melanonychia, and specific immunohistochemical staining patterns. In this case, the uniformly pigmented patch on the proximal nail fold prompted a thorough physical examination and biopsy, leading to the timely diagnosis and management of the lesion.
The location of the lesion in the proximal nail fold is rare, and the absence of HPV infection in this case adds to its uniqueness. The presence of a uniformly pigmented patch in a young Chinese individual further highlights the importance of considering pigmented Bowen disease in the differential diagnosis of pigmented lesions around the nail fold. Early recognition and intervention are crucial, as squamous cell carcinoma is highly invasive and can lead to fatal metastasis if not treated promptly.
In conclusion, this case underscores the importance of a thorough clinical evaluation and histopathologic examination in diagnosing pigmented Bowen disease, especially in rare locations such as the proximal nail fold. The idiopathic etiology and absence of HPV infection in this case add to the existing knowledge of this rare condition. Timely diagnosis and complete excision are essential to prevent disease progression and ensure favorable outcomes.
doi.org/10.1097/CM9.0000000000000845
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