Diagnosing And Treating A Pigmented Lesion On The Hallux

Naohiro Shibuya, DPM, MS, FACFAS

A 66-year old Caucasian male with a history of controlled diabetes, hypertension, hyperlipidemia, psoriasis, obstructive sleep apnea and post-traumatic stress disorder received a referral by dermatology to our surgery department. The referral was for surgical treatment of a suspicious lesion in the left hallux.

   The patient initially noticed the lesion approximately two months prior and it had been growing in size since then. He was worried about malignancy since his father died of malignant melanoma. He did not recall any trauma. He did not have any associated pain or discomfort. The patient was taking bupropion (Wellbutrin, GlaxoSmithKline), diclofenac (Voltaren, Novartis), fexofenadine (Allegra, Chattem), gabapentin (Neurontin, Pfizer), gemfibrozil (Lopid, Pfizer), metformin, metoprolol (Lopressor, Novartis) and pravastatin (Pravachol, Bristol-Myers Squibb) daily. He was allergic to codeine, cephalexin and fish oil. He denied any constitutional symptoms.

   The clinical examination revealed a hyperpigmented lesion of 2 x 3 mm on the medial aspect of the left hallux. The lesion was mildly raised and had three distinct hyperpigmented areas of different shades of red and purple. There was no satellite lesion. The lesion was asymmetrical and had an irregular border.

Key Questions To Consider

1. What questions should a physician ask the patient?
2. What is the differential diagnosis?
3. How common is melanoma in the foot?
4. What are the risk factors for melanoma?
5. What is the proper biopsy technique?

Answering The Key Diagnostic Questions

1. Have any of your family members had melanoma? What is your racial background? Have you had any puncture wound in your feet? Has the lesion grown lately?
2. The differential diagnosis includes: melanoma, dysplastic nevus, seborrheic keratosis, solar lentigines, dermatofibroma, pigmented basal cell carcinoma and verruca.
3. Melanoma in the feet is rare in light-skinned patients. However, in patients with pigmented skin, it is very common. Identification of risk factors is important.
4. Known foot specific risk factors include dark skin, a history of puncture trauma, a family history of melanoma and a high nevus count.
5. Excisional, full-thickness biopsy of 1 mm border is recommended for a smaller lesion and incisional (typically punch) biopsy is recommended for a large lesion.

A Guide To The Differential Diagnosis

Dysplastic nevus. It is also referred to as an atypical mole. Having multiple atypical moles is associated with development of melanoma. Clinically, this resembles melanoma. Biopsy rules out the malignant lesion.

   Seborrheic keratosis. This is a very common, raised or flat benign lesion, which often appears as black, gray, pale or purple in older patients. It can mimic melanoma or verruca. It is benign and no treatment is necessary. The lesion only affects the epidermis.

   Solar lentigo. It is also known as a liver spot, sun-induced freckle or senile lentigo. It is very common in older patients. The lesions are induced by ultraviolet light. Therefore, they are not common in the foot for those who live in the northern part of the United States. Lentigo simplex, however, is not caused by UV light and can develop during childhood. Both are benign.

   Dermatofibroma. This nodular skin lesion is one of the most common skin lesions that occur in the extremities of women. It is normally asymptomatic and benign. No treatment is necessary unless the condition is painful.

   Pigmented basal cell carcinoma. A basal cell carcinoma can be pigmented and mimic a melanoma. Pigmentation of a basal cell carcinoma is more common in Asians. It is rare in Caucasians.

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