Case of a New, Irregular Pigmented Lesion on the Plantar Surface of the Foot

Case at a Glance

A 35-year-old female with a history of Hashimoto's disease and a family history of skin cancer presents with a newly discovered, large, irregularly shaped pigmented lesion on the sole of her foot, raising concerns for acral lentiginous melanoma versus a traumatic hemorrhage.

Patient's Story

The patient, a 35-year-old female, presented for consultation after recently discovering a new pigmented lesion on the plantar surface of her foot. She described the lesion as being large and having an irregular border. The patient denied any specific trauma or injury to the foot. She expressed significant concern due to a family history of skin cancer and has an annual dermatology appointment scheduled in the near future.

Initial Assessment

Upon initial presentation (via patient report and a provided image), the lesion was a pigmented macule of significant size with irregular borders, located on the non-sun-exposed skin of the foot's sole. The patient's medical history is notable for Hashimoto's disease, managed with levothyroxine. Her family history of skin cancer is a significant risk factor.

The Diagnostic Journey

The primary concern, given the location (acral skin), recent appearance, and irregular morphology, was the potential for acral lentiginous melanoma. However, a key differential diagnosis considered was a subcorneal hemorrhage or talon noir, which can mimic melanoma. This possibility was raised despite the patient's assertion of no known trauma, as minor, unnoticed injuries to the foot are common. The diagnostic plan was to proceed with her scheduled dermatology appointment for a professional evaluation, which would include a physical examination and dermoscopy to assess the lesion's pattern and features more closely.

Final Diagnosis

Pending Dermatological Evaluation. The differential diagnosis remains between a benign traumatic hemorrhage (bruise) and a malignant melanoma.

Treatment Plan

Awaiting definitive diagnosis. If dermoscopy is inconclusive or suspicious for malignancy, a biopsy (shave or punch) would be the next step for histopathological examination. If the lesion is identified as a hemorrhage, no treatment is necessary, and it would be expected to resolve over several weeks. If diagnosed as melanoma, a wide local excision would be required, with further treatment depending on the tumor's depth and stage.

Outcome and Follow-up

The patient is scheduled for an imminent dermatology appointment for a comprehensive evaluation. Close follow-up is essential. She was advised to monitor the lesion for any changes in size, shape, or color while awaiting her appointment. Given her family history, continued annual full-body skin examinations are strongly recommended.