What condition is characterized by discoloration or change in thickness of the nail plate?

The condition characterized by discoloration or change in thickness of the nail plate is onychomycosis. This is a fungal infection that affects the nails, leading to various symptoms such as thickening, discoloration (which may include yellow or white spots), and even crumbling of the nail. As the infection progresses, it can cause significant changes in the nail's texture and appearance, often making it appear irregular and sometimes even painful.

It is important to understand that while other conditions like onychatrophia, hematoma, and onycholysis may also affect the nails, they do not specifically focus on fungal infections leading to thickening and discoloration as prominently as onychomycosis does. Onychatrophia refers to the wasting away or atrophy of the nail. Hematoma involves bleeding under the nail due to injury, presenting primarily as discoloration without the thickening changes typical of fungal infections. Onycholysis, on the other hand, describes the separation of the nail plate from the nail bed but does not inherently involve the same thickness and discoloration changes seen in onychomycosis. Thus, onychomycosis stands out as the correct answer based on its specific characteristics.