Which nail disorder is characterized by lines or ridges running vertically from the cuticle to the tip?

The nail disorder characterized by lines or ridges running vertically from the cuticle to the tip is onychorrhexis. This condition manifests as brittle nails that may develop vertical ridges, which occur due to a variety of factors including genetics, aging, and environmental conditions. The presence of these ridges indicates issues with the nail matrix, where the nail is formed, and can be a sign of underlying health problems or nutritional deficiencies.

In contrast, onychomycosis involves a fungal infection of the nails that typically results in discoloration or thickening rather than ridges. Paronychia is an infection of the tissue surrounding the nail, which can cause redness, swelling, and pus but does not lead to the formation of ridges. Psoriasis, on the other hand, can affect the nails and induce changes such as pitting or discoloration, but it does not specifically result in the vertical lines that define onychorrhexis. Thus, onychorrhexis specifically describes the condition of having vertical lines or ridges along the nail, making it the correct answer.