Which of the following nail diseases is not caused by fungus?

The correct answer is Onychatropia, as this condition is characterized by the abnormal loss of the nail. Onychatropia is associated with various factors such as trauma, systemic diseases, or other non-fungal issues, rather than being caused by a fungal infection.

In contrast, onychomycosis refers specifically to a fungal infection of the nail, causing changes in thickness, color, and integrity of the nail. Leuconychia, which presents as white spots or discolorations on the nails, can sometimes result from external factors or systemic health issues, but it is not directly linked to fungal infections. Onychorrhexis involves the splitting or brittle condition of the nails, which can be due to several non-fungal factors including environmental and health-related causes.

Understanding the distinctions among these conditions is crucial for correctly diagnosing nail disorders and choosing appropriate treatments.