A patient aged 37 years presented complaining of the nail changes in his bilateral thumbnails. He denied trauma to the nail. He was otherwise healthy, but was very distressed by the appearance of his nails.
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Median canaliform nail dystrophy, also known as dystrophia unguis mediana canaliformis, solenonychia, or median canaliform dystrophy of Heller, refers to a midline longitudinal dent, groove, or split of the nail, most often seen on the thumb.
Depending on the cause, this disorder can originate at the proximal nail fold or more distally. It usually presents as a single longitudinal defect with lateral projections resembling a fir tree.
Several etiologies have been suggested for this phenomenon. Most cases have been linked to trauma, either from repetitive tasks that involve the nail, such as typing on a cell phone, or as a single traumatic event to the digit.
Usually, the deformity resolves when the trauma is relieved, but other cases can persist, which suggests permanent damage to the nail matrix. In some cases, the median canaliform nail dystrophy (MCND) can reappear years after its disappearance.
Growths in the nail matrix, such as a papilloma or glomus tumor, can produce this appearance. Reports of familial instances of MCND exist, suggesting a possible genetic cause, with onset at an early adulthood. These familial causes have not been associated with any other familial syndromes.
Finally, this deformity has been observed with onset at the time of isotretinoin therapy, with resolution after stopping the therapy.
Treatment has had inconsistent results due to the numerous causes. In some patients, 0.1% tacrolimus ointment over the proximal nail fold without occlusion has resulted in improvement in some patients, with minimal adverse effects.
Injecting triamcinolone acetonide into the nail plate has previously been used, but with inconsistent results and considerable pain to the patient.
Psoriasis is a papulosquamous inflammatory skin disorder. Nail findings in psoriasis include pitting, onycholysis, subungual hyperkeratosis, oil spots, and nail crumbling.
Also known as leukonychia striata or transverse leukonychia, Mee’s lines is the appearance of multiple, white, parallel, transverse lines across the nail plate of several or all digits. It can be a normal variant, or it can appear from minor trauma, such as manicures.
Mee’s lines has also been associated with drug use such as chemotherapeutic agents or poisoning with arsenic or thallium. It can also be seen in systemic illnesses such as Kawasaki’s or HIV.
Onycholysis is the separation of the nail plate from the nail bed. It is most often caused by psoriasis or onychomycosis. Significant nail trauma can also be a cause.
Other causes include hand dermatitis (eczema), herpes, hypo/hyperthyroidism, and porphyria. Treatment includes maintaining a dry nail bed and clipping away any excess nail.
Jason Preissig, MD, is a graduate of Baylor College of Medicine.
Adam Rees, MD, a graduate of the David Geffen School of Medicine at UCLA, practices dermatology in Los Angeles.
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- Perrin AJ, Lam JM. CMAJ. 2014; doi: 10.1503/cmaj.121942.