Acral lentiginous melanoma misdiagnosed as verruca plantaris: A case report
Department of Dermatology, Baylor College of Medicine, Houston, Texas. firstname.lastname@example.org
The ratio of acral lentiginous melanoma (ALM) to all melanomas among Caucasians is small, although this type of malignant melanocytic neoplasm comprises the majority of melanomas among those who have darker skin tone. Because of frequently atypical clinical morphology, and as a consequence of their relative rarity, ALM is often misdiagnosed. This case demonstrates the disastrous consequences of prolonged treatment of an ALM presumed to be a plantar wart. Pedal lesions require close observation and prompt biopsy when diagnostic uncertainty exists or when therapeutic interventions fail.
The ratio of acral lentiginous melanoma (ALM) to other types of malignant melanocytic neoplasms varies among ethnic groups, being lower in Caucasians and higher in Asians and African-Americans. A definitive diagnosis may be delayed because of either equivocal clinical morphology or a low index of suspicion. As a consequence, the prognosis of ALM is often poor. The case of a middle-aged fair-skinned woman with ALM that was mistaken for verruca plantaris is presented to highlight the difficulty in diagnosing such lesions.
A 42-year-old woman of Scandinavian descent sought medical attention for a non-healing lesion present for approximately 1 year on the sole of her right foot. The patient had been seen by both a primary care physician and a dermatologist and had received innumerable treatments with liquid-nitrogen cryospray and topical application of cantharidin solution for the presumptive diagnosis of verruca plantaris. Her past medical history, social history, and family history were unremarkable. The patient specifically denied prior trauma or radiation to the affected area.
Physical examination disclosed a 4.2 by 3.0 cm ulcerated nodule located on the proximal portion of the right heel. The lesion also demonstrated a central exophytic granulation-tissue-like mass as well as peripherally scattered small jet-black foci (Fig. 1). The surrounding skin was hypopigmented and appeared to be macerated. A potassium hydroxide preparation taken from the lesion's edge was negative as was a fungal culture. An ellipitical incisional biopsy was obtained which included the peripheral white area, the central fleshy material, and a focus of dark pigmentation. Histopathological examination revealed cytologically atypical melanocytes at the basal layer of the epidermis as well as pagetoid spread of melanocytes. Nests of similar atypical melanocytes were found in the papillary and upper reticular dermis. A moderate lymphohistiocytic infiltrate was present at the tumor border. Subsequent complete excision confirmed the diagnosis of ALM; tumor thickness was estimated to be 13 mm and invasion was into the subcutaneous tissue (Clark's level V). Serum LDH level was normal as were radiologic evaluations of the lungs, bones, and liver. After 6 months the patient presented with pain and shortness of breath secondary to widespread bone and pulmonary metastases. Neither radiotherapy nor biochemotherapy was effective, and the patient ultimately succumbed to complications from metastatic disease.
Acral lentiginous melanoma is the most common type of melanoma found in individuals with darkly pigmented skin (natives of Asia, India, Africa, and African-Americans); it also constitutes a smaller proportion of all melanomas found in fair-skinned persons [1, 2, 3, 4]. Acral lentiginous melanoma is found on the digits, palms, soles, dorsum of the foot, and in the subungual area [1, 2, 3, 4, 5, 6, 7]. Because of these unusual sites, and because of its atypical clinical morphologies, ALM is frequently misdiagnosed and may receive prolonged courses of inadequate or inappropriate therapy [8, 9, 10]. The most recent survey of ALM indicated that up to one-third may be initially misdiagnosed . Acral lentiginous melanoma can be mistaken for a variety of alternative diagnoses, including verruca, corn or callus, eccrine poroma, pyogenic granuloma, ischemic ulceration, mal perforans from a peripheral neuropathy, gangrene, superficial fungal infection, traumatic residual, foreign body, and benign nevus [10, 11, 13]. In the present case a minimally pigmented eroded nodule on the heel of a Caucasian individual was mistakenly diagnosed as a plantar wart, which in turn led to 12 months of inadequate therapeutic intervention. It should be noted that the converse is also occasionally possible. That is, non-melanocytic plantar lesions (such as chromhidrosis, mycetoma, tinea nigra, and hemangiomata) may be misdiagnosed clinically as melanoma.
Foot lesions are often overlooked entirely by both patient and physician. Even if discovered, both patients and their healthcare providers may not readily think of melanoma as likely, and delay in diagnosis is the result of both patient and physician factors . This multifactorial delay may stretch from months to years, thereby adversely affecting the overall patient prognosis [14, 15, 16]. Pedal lesions require close observation and early biopsy if any clinical uncertainty exists.
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