Differential Diagnosis for Thick Toenail and Black Big Toe
Single Most Likely Diagnosis
- Onychomycosis (Fungal Infection of the Nail): This is the most common cause of thickened and discolored toenails. The fungal infection can cause the nail to become thick, brittle, and discolored, often turning black due to debris accumulation under the nail.
Other Likely Diagnoses
- Trauma: Repeated trauma to the toenail, such as from poorly fitting shoes or frequent stubbing, can cause thickening and discoloration of the nail.
- Onychauxis (Nail Thickening): A condition characterized by thickening of the nail without any apparent cause, which can sometimes lead to discoloration.
- Melanonychia (Nail Pigmentation): A condition where there is pigmentation of the nail, which can cause black streaks or spots on the nail, potentially leading to a uniformly black appearance if the pigmentation is extensive.
Do Not Miss Diagnoses
- Subungual Melanoma: A type of skin cancer that can occur under the nail, causing thickening and dark pigmentation. Although rare, it is crucial to rule out this condition due to its potential severity and the importance of early detection.
- Subungual Hematoma: Bleeding under the nail, often due to trauma, which can cause the nail to appear black. This condition can sometimes be associated with more serious injuries, especially if the trauma was significant.
Rare Diagnoses
- Sarcoidosis: A systemic disease that can affect multiple parts of the body, including the skin and nails. Nail involvement can lead to thickening and discoloration, although this is a rare manifestation.
- Psoriasis: While more commonly associated with skin lesions, psoriasis can also affect the nails, leading to thickening, pitting, and discoloration in some cases.
- Darier's Disease: A rare genetic disorder that affects the skin and sometimes the nails, leading to abnormalities such as thickening and discoloration.