Differential Diagnosis for Brown Pinky Toe

Single most likely diagnosis

• Fungal infection (onychomycosis or tinea pedis): The description of a brown discoloration on the entire toe, particularly the pinky toe, is highly suggestive of a fungal infection. Fungi thrive in warm, moist environments, and the feet, especially between the toes, provide an ideal setting for fungal growth.

Other Likely diagnoses

• Bacterial infection (paronychia or cellulitis): Bacterial infections can cause redness, swelling, and discoloration of the toe. While less likely than fungal infections for a brown discoloration, they are common and should be considered, especially if there's a history of trauma or exposure to bacteria.
• Eczema/Dermatitis: Eczema or dermatitis on the foot can lead to changes in skin color, including brownish discoloration, due to chronic inflammation and skin thickening.
• Trauma: Physical injury to the toe can cause bruising or changes in skin pigmentation, leading to a brown appearance.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed)

• Diabetic foot ulcer or infection: In patients with diabetes, any foot lesion can be a sign of a more serious underlying condition, such as a foot ulcer or infection, which can lead to severe complications if not promptly treated.
• Melanoma: Although rare, melanoma can present as a new or changing pigmented lesion on the foot. Given the potential for malignancy, it's crucial to consider this diagnosis, especially if the lesion is new, changing, or has irregular borders.
• Peripheral artery disease (PAD): PAD can cause changes in skin color and temperature of the feet due to reduced blood flow. While not directly causing a brown toe, it's a condition that requires medical attention to prevent further complications.

Rare diagnoses

• Arsenic poisoning: Chronic exposure to arsenic can cause pigmentation changes in the skin, including a brownish discoloration on the feet.
• Addison's disease: This rare endocrine disorder can cause hyperpigmentation, leading to darkening of the skin, which might be noticed on the feet.
• Pityriasis versicolor: A fungal infection caused by Malassezia yeast, which can lead to changes in skin pigmentation, resulting in brown patches.

Each of these diagnoses has different management strategies, ranging from topical antifungals for fungal infections to more complex treatments for conditions like melanoma or PAD. Accurate diagnosis through clinical examination and, if necessary, laboratory tests is essential for appropriate management.