Retronychia occurs when the nail plate (the hard part of the nail made of the protein keratin) grows into the nail fold. Multiple generations of new nail plates can then grow on top of one another in a stack under the old nail plate because the nail matrix and the old nail plate are no longer aligned. The growth of a new nail plate pushes the old nail upwards.
Retronychia most often affects the big toenails and is caused by repetitive injury to the nail, most often by wearing tight shoes or by doing activities that lead to toenail injury.
In the acute stage, this condition is painful and causes inflammation of the nail fold, yellow or white discoloration of the nail plate (xanthonychia), and growth of new connective tissue on the inflamed areas (granulation tissue).
In the chronic stage, the inflammation resolves, but the nail plate becomes thickened and separates from the nail bed. Layers of nail plates can become stacked, and the cuticle is missing. There are layers to the nail, and little or no debris accumulates under the nail. Tissues around the nail may also be swollen, red, and tender. Testing may help differentiate onychomycosis from retronychia but only sometimes.
Doctors diagnose chronic retronychia by its appearance, including the layers of nail plate and the missing cuticle.
(See also Acute Paronychia Acute Paronychia Acute paronychia is a bacterial infection of the nail fold. In acute paronychia, bacteria (usually Staphylococcus aureus or streptococci) enter through a break in the skin resulting from a hangnail... read more and Chronic Paronychia Chronic Paronychia Chronic paronychia is recurring or persistent inflammation of the nail fold, typically of the fingernails. (See also Acute Paronychia.) Chronic paronychia occurs almost always in people whose... read more .)
Corticosteroids and nail removal
In the acute stage, treatment options include corticosteroids that are applied to the nail and corticosteroids that are injected into the nail. In the chronic stage, the nail is removed.
People should avoid doing activities that injure the nail and wear shoes with more space around the toes to relieve pressure on the affected toenail.