Squamous cell carcinoma is a common carcinoma of the nail, but Bowen’s disease - SCC in situ is rarely diagnosed. Longitudinal Erythronychy (LE) is one of the most underestimated clinical presentations [1,2]. There are several differential diagnoses including other neoplasias, scars, inflammatory and infectious origins. It is therefore always useful in many cases to make a clinico-pathological correlation to retain the diagnosis. Malignancy is uncommon, but not rare, squamous cell carcinoma in situ is the most common malignancy. We report a case of subungual Bowen disease revealed by longitudinal erythronchia in a 38-year-old woman.

      We report a case of a 38-year-old woman with no significant medical history, presented to our departement of dermatology with a 4-years history of a 2-mm-wide longitudinal erythronychia band on the 3rd left nail of the dominant hand with no history of infection, trauma or radiation. Clinical examination revealed the presence of a longitudinal erythematous band with distal encoched onycholysis. Dermoscopy showed longitudinal erythronychia followed by leukonychia and at the free edge of the nail: Subungual keratosis in the junction area between the nail plate and the band. After avulsion of the nail plate, a longitudinal excision biopsy of the nail unit including the distal matrix, the nail bed and the hyponychium was then performed. Anathomopathology showed a proliferation of keratinocytes that were atypical and non-aligned in the epidermis of the proximal and nail matrix beds, with normal aligned keratinocytes in the distal side. We retained the diagnosis of subungual bowen disease and additional excision was performed accordingly. Five months later, there was no evidence of recurrence.

      Subungual Bowen disease remains uncommon, often diagnosed late. The age of onset is between 50 to 70 years old with a male predominance and it sits most often at the nails of the first three fingers of the left hand [4,5]. The duration of evolution of lesions at presentation varies between 3 to 5 years.

      At the beginning the lesion sits at the lateral nailfold with a progressive extension towards the nail bed and the matrix. Distal onycholysis may occur and is related to the presence of abnormal keratin in the nail bed which may also cause nail dystrophy or detachment of the nail plate. Dermatoscopy of subungual bowen disease is not clearly described in the literature; In our case, it appears to be the primary differential diagnosis of a benign tumor called onychopapilloma [6,7]. This diagnosis is confirmed by histopathological examination. The treatment of choice is based on the total surgical excision of the tumor for curative and conservative purposes taking into account the aesthetic concern. This attitude implies a good comprehension of the anatomy of the nail apparatus in view of the technical difficulties that can be encountered [5]. Mohs surgery for nail tumors is well established and increasingly used [5].

      Not every longitudinal erythronychia with subungueal hyperkeratosis should be considered onychopapilloma ; but practicians should be aware and perform a histopathological diagnosis to confirm the diagnosis.

Figure 1: Subungual Bowen disease. A: Clinical image of Longitudinal erythronychia. B: Dermatoscopic image of nail plate. C: Five months after surgery