Case Presentation: A 58-year-old man with type 2 diabetes, hypertension, peripheral arterial disease, and right fifth toe amputation for osteomyelitis presented to the emergency room with pain at the site of a non-healing right foot ulcer. When the pain started two years prior, the patient was diagnosed with a diabetic foot infection (DFI) from poorly controlled type 2 diabetes. The ulcer persisted after several courses of antibiotics and improvement in his hemoglobin A1c from 11.2% to 7.1%. The patient was admitted two months prior for management of the ulcer and discharged without complication after undergoing excisional debridement for infection and anterior tibialis angioplasty. On exam, the patient was tachycardic to 113 bpm and a large area of fluctuance was noted near the 3×5 cm plantar ulcer. Further examination revealed a firm, tender mass in the right inguinal region. Laboratory results included a WBC count of 16.9. Broad-spectrum antibiotics were initiated and an MRI revealed an enlarging 5×4 cm plantar right foot soft tissue mass. Wide local excision was performed and punch biopsies were sent for analysis. Ultrasound of the right inguinal mass revealed possible abscess formation, however, despite IV antibiotic therapy the mass continued to enlarge prompting an excisional biopsy which revealed metastatic malignant melanoma consistent with pathology from the right foot mass. The patient was discharged with oncology follow-up.
Discussion: Non-healing, intractable foot ulcers require further workup; misdiagnosed cases of melanoma presenting as foot ulcers have been reported. The threshold for obtaining special imaging, requesting consultation, and admitting for hospitalization in patients with DFIs can be difficult to determine. DFIs should be evaluated at 3 levels: the wound including severity and depth of infection, the affected foot including vascular assessment, and the patient as a whole.[1] Consideration of the patient as a whole prompts deeper investigation in this case. Atypical physical exam findings such as inguinal lymphadenopathy and outpatient treatment failure prompted consideration of alternate diagnoses. Melanoma was considered early in the hospitalization since the skin of the lower extremities is the most common site of inguinal node metastasis.[2] Some studies report poor prognosis of melanoma presenting as foot ulcer likely due to delayed diagnosis and prolonged course of inadequate therapy.[3]
Conclusions: Melanoma and skin cancers are a rare cause of DFI and diagnosis can be challenging. Suspicious features should prompt early consideration of special imaging, consultation, and hospitalization.
