Diagnosis: Habit-tic deformity
Habit-tic deformity is a common nail condition caused by a conscious or unconscious rubbing or picking of the proximal nail folds. Horizontal grooves are formed proximally due to nail matrix damage and subsequently move distally with fingernail growth. The dominant thumbnail is most often affected by frequent rubbing with the ipsilateral index fingernail, although all nails can be involved.
This deformity is more common during periods of stress—which my patient was experiencing in his new role as an intelligence officer—and is believed to result from a compulsive or impulse control disorder.
Differential diagnosis includes onychomycosis
The differential diagnosis of external nail deformation includes median nail dystrophy, chronic proximal nail fold inflammation, onychomycosis, psoriasis, Beau’s lines, and habit-tic-like dystrophy.
Median nail dystrophy. This nail deformity has a distinctive longitudinal split in the center of the nail plate with several cracks projecting laterally, resembling a fir tree. The etiology of this disorder is unknown, although some have suggested that habit-tic deformity and median nail dystrophy are different manifestations of the same disorder.1
Chronic proximal nail fold inflammation. Chronic paronychia is an inflammation of the proximal nail fold, and is one of 2 forms of inflammation included in the differential. It is characterized by tenderness and swelling around the proximal and lateral nail folds, most often due to contact irritant exposure. The cuticle separates from the nail plate, which creates a space for infection. The nail plate surface subsequently becomes brown and develops ripples that can mimic the habit-tic deformity. Chronic eczematous inflammation is the second form of inflammation in the differential and can produce results that are similar to chronic paronychia. Both forms of proximal nail fold inflammation tend to resemble rounded waves, as opposed to the narrow, closely spaced grooves seen in habit-tic deformity.
Onychomycosis. Habit-tic deformity is often confused with onychomycosis, though the 2 can be easily distinguished upon close inspection. Unlike habit-tic deformity, onychomycosis classically has nail thickening and hyperkeratotic debris. Diagnosis can be solidified by a potassium hydroxide examination and culture.
Psoriasis. Psoriatic nail lesions can occur in the absence of classic skin findings. Nail pitting is the hallmark nail finding in psoriasis. Other findings such as onycholysis (separation of the nail from the nail bed), nail fragmentation and crumbling, and splinter hemorrhages can distinguish psoriatic nails from habit-tic deformity.