A 56-year-old man is referred to dermatology for evaluation of a “fungal infection” that has affected both thumbnails for at least 20 years. While the condition produces no symptoms, it has nonetheless been a source of constant embarrassment to him.

He denies having any such problems with his toenails. Furthermore, he says the problem has persisted despite the use of numerous topical and oral medications, including topical miconazole, clotrimazole, oil of eucalyptus, bleach, and the oral antifungals terbinafine and griseofulvin. None of these has had any effect.

Additional history taking reveals that the patient is highly allergy-prone; he had seasonal allergies and asthma as a child. He also has a history of extremely dry and sensitive skin.

On examination, the problems with the patient’s thumbnails are obvious, with traumatic absence of cuticles, widening and deepening of the cuticular sulcus, and deep parallel transverse lines involving the entire visible nail plates. Scattered subungual patches of brown discoloration are also seen beneath the lines. None of the patient’s other nails are abnormal in any way.

ANSWER
The correct answer is habit-tic deformity (choice “d”), a relatively common self-inflicted condition relegated to thumbnails.

Chronic candidal paronychia (choice “a”) has certain similarities to habit-tic deformity (eg, loss of connection between cuticle and nail plate) but it also has an inflammatory aspect that manifests as chronic focal tenderness, redness, and swelling of the adjacent perionychial tissue.

The clinical picture and total lack of response to antifungal medications made a diagnosis of onychomycosis (choice “b”) quite unlikely. Canaliformis defect (choice “c”) involves a central longitudinal linear concave defect in the affected nails and is therefore incorrect.

DISCUSSION
Fungal infection in fingernails, while not unknown, is about 18 times less likely than the same condition in toenails. Nonetheless, onychomycosis continues to be vastly overdiagnosed by clinicians whose differential diagnoses are lacking.

Habit-tic deformity is a perfect example of this phenomenon. Also called onychotillomania, habit-tic is actually caused by chronic picking of the cuticles; over time, this results in the creation of transverse parallel grooves that persist for the 4 to 4.5 months it takes for the nail plate to grow out. It rarely occurs on fingernails other than the thumbnails. Habit-tic, as in this case, can also involve modest traumatically induced subungual bleeding, seen as brownish discoloration.

Many patients have good insight into their causative role, but just as many pick their cuticle unconsciously. The obvious solution is to stop the offending behavior and/or put a barrier on the nails, but neither measure has met with much success. One potential remedy (see “Suggested Reading”) is to fill the cuticular sulcus with protective acrylate glue and let it dry. This, in effect, creates a barrier while the cuticle heals and reattaches to the nail plate (although the potential for contact dermatitis may become a concern). Hypnosis and other behavior modification have also been tried.

For many patients, just knowing what they don’t have is quite helpful. For providers, it is helpful to develop a differential for conditions that involve nail dystrophy, including the incorrect answer choices offered here. If fungal infection were truly a possibility, the best way to confirm that diagnosis would be to send a nail clipping to pathology, either for sectioning and identification of fungal elements or an actual fungal culture.

SUGGESTED READING
Ring DS. Inexpensive solution for habit-tic deformity. Arch Dermatol. 2010;146(11):1222-1223.