Differential Diagnosis for the Dark-Brownish Foreskin Lesion

• Single Most Likely Diagnosis
  • Seborrheic Keratosis: Given the patient's report of a consistent symmetry, border, shape, size, and color for the past 40 years, seborrheic keratosis is a strong consideration. This condition is common in older adults and can present as a dark-brownish lesion. The long-standing nature and stability of the lesion's characteristics over time support this diagnosis.
• Other Likely Diagnoses
  • Melanocytic Nevus (Mole): Although the patient reports no changes, a mole could present similarly. The description of the lesion as dark-brownish could be consistent with a benign melanocytic nevus.
  • Dermatofibroma: These are common, benign skin lesions that can appear as firm, brownish to purple nodules. They often have a long history without change, which fits the patient's description.
• Do Not Miss Diagnoses
  • Squamous Cell Carcinoma (SCC): Although less likely given the long history without change, SCC can present as a pigmented lesion. It's crucial to consider this diagnosis due to its potential for malignancy and the importance of early detection.
  • Melanoma: Despite the patient's report of no changes, melanoma must be considered in the differential diagnosis of any pigmented skin lesion due to its potential for aggressive behavior and high mortality if not caught early.
• Rare Diagnoses
  • Malignant Melanotic Macule of the Penis: A rare condition that could present with pigmentation changes. It's less likely but should be considered due to its potential severity.
  • Kaposi's Sarcoma: This is a rare tumor that can appear as pigmented lesions, especially in immunocompromised patients. It's unlikely but should be kept in mind, especially if the patient has risk factors for immunosuppression.