Amelanotic subungual melanoma and chilblains

Abstract

A female patient in her 50s presented with blue discolouration of several toes and with single nail dystrophy affecting the little toenail. The nail changes were considered to be secondary to poor circulation and chilblains, which led to delay in the diagnosis of amelanotic subungual melanoma.

Background

Amelanotic subungual melanoma is an uncommon presentation of melanoma, hence causing a delayed diagnosis and resulting in poor prognosis. In our case, the diagnosis was further delayed because of unrelated skin changes on the toes. The case demonstrates how Occam’s razor can fail the physician if a high level of suspicion is not maintained, especially when the stakes are high, as is the case in melanoma. Our case supports having a low threshold for nail biopsy in case of persistent onychodystrophy of a single nail, especially if the patient reports episodes of bleeding or pain.

Case presentation

A Caucasian female patient in her 50s was referred to the dermatology clinic with 4 months’ history of throbbing pain from the left little toe. She also had nail dystrophy with most of the nails coming off. She had bought a new pair of shoes for work 4 months prior and her problems started shortly after. She had been treated with antibiotics by her general practitioner (GP) for presumed toenail infection. She also reported purplish discolouration of the same toe and several other toes on both feet. Apart from irritable bowel syndrome, she had no significant medical history. She was not on any regular medication. She had a smoking history of 30 pack-years.

On initial examination in the clinic, there was marked bluish discolouration of the toes (figure 1). The nail plate had almost completely come off from the left little toe. A small area on the medial aspect showed nail plate thickening and yellow discolouration. There were no exophytic or granulomatous growths and no pigment was noticed.

Figure 1.

Bluish discolouration of the toes. The left little toenail is dystrophic with a non-specific yellow crust distally.

Based on the history and clinical presentation, the following differential diagnoses were discussed: acrocyanosis, chilblains, peripheral vascular disease, trauma, nail bed tumour and onychomycosis.

Nail clippings were taken for fungal microscopy and culture, which came back negative. On her follow-up appointment in clinic 4 months later, she continued to have similar symptoms. On examination, she had purplish discolouration on all toes but most prominent on the left little toe, left middle toe and both big toes. There was nail plate crumbling on the left little toe along with distal onycholysis. There was some yellow discolouration of both big toenails, but apart from this, all other toenails were normal. Her dorsalis pedis pulses were present on both feet and her toes were cold to touch. She was referred to vascular surgeons for assessment. She was advised to stop smoking and was started on aspirin. Her screening blood tests for antinuclear antibodies, antiphospholipid antibodies and cryoglobulin were normal. She was advised to avoid exposure to cold and to wear comfortable shoes.

At her follow-up 1 month later, her symptoms were better apart from а small yellowish crust on the left little toe. The patient mentioned that there had been аn episode of bleeding in the last month and she could not recall preceding trauma. On dermatoscopic examination, there was no pigmentation or any suspicious features. As her symptoms had improved, she was discharged from the dermatology follow-up.

She was referred back by her GP 1 year later, as her left little toenail continued to ooze and crust resulting in increasing pain and difficulty in walking. On examination, she had honeycomb crusting on her left little toe. Her toenail was removed and a biopsy was obtained from the nail bed. Her biopsy came back as an invasive melanoma. She had amputation of the left little toe under the plastic surgeons. The histolopathology results showed this to be a completely excised stage 1B melanoma.

Outcome and follow-up

Unfortunately, 3 years after the excision, she was diagnosed with metastatic melanoma in the left groin lymph nodes for which she had left inguinal lymph node dissection and was started on adjuvant anti-PD1 immunotherapy with pembrolizumab, which she completed after 1 year. Since then, in the last year, she continues to have six monthly follow-up appointments and has not had disease recurrence.

Discussion

Amelanotic subungual melanoma can be very difficult to diagnose clinically, dermoscopically and sometimes even pathologically. Because of its non-specific clinical features, it is very often mistaken for onychomycosis,¹ pyogenic granuloma, lichen planus, glomus tumour, etc.² Although in general, subungual melanoma is more common in black Africans and Asians, it has been suggested that subungual amelanotic melanoma occurs mainly in the Caucasian population with a predilection for the female gender.² In case of granulating masses in the nail or periungual tissues, avoiding prolonged periods of conservative treatment for presumed ingrown nails has been advised.³

Due to absence of any exophytic or granulomatous lesion or pigment, positive history of trauma from footwear and the fact that the nail of the little toe was involved, led to a significant delay of diagnosis in our patient. This case also highlights another difficult aspect in diagnosing amelanotic subungual melanoma. Our patient presented with marked bluish discolouration of the toes suggestive of pernio (chilblains) or acrocyanosis, which deterred our attention away from the melanoma. In patients with problems affecting the lower legs, the clinician could be reluctant to do a biopsy out of fear of prolonged healing, which can lead to delayed/missed diagnosis of melanoma.

Nail deformities have been reported in patients with pernio after extended exposure to cold.⁴ Nail changes in chilblains mimicking lichen planus have also been described.⁵ Onychodystrophy has been suggested as a possible marker for peripheral artery disease.⁶ Such scenarios offer a single explanation for both problems (dystrophic nail and blue toes), and thus better satisfy the Occam’s razor principle. Our case demonstrates how Occam’s razor can fail the dermatologist if a high level of suspicion is not maintained, especially when the stakes are high, as is the case in melanoma. This is especially true in modern days with the abundance of easily accessible medical information online, where one can find case reports in confirmation of almost any clinical hypothesis. Our case supports having a low threshold for nail biopsy in case of persistent onychodystrophy of a single nail, especially if the patient reports episodes of bleeding or pain.

Learning points.

• Amelanotic subungual melanoma has non-specific clinical features and is often mistaken for onychomycosis or ingrown nail with granulation tissue.

• Diagnosing amelanotic subungual melanoma can be more difficult in patients with circulation problems affecting the lower legs, which could either deter attention from the melanoma or make the clinician reluctant to do a biopsy out of fear of prolonged healing.

• A low threshold for nail biopsy in cases of persistent onychodystrophy of a single nail is advised, especially if the patient reports episodes of bleeding or pain.

Ethics statements

Patient consent for publication

Obtained.