Are You Confident of the Diagnosis?
What you should be alert for in the history
Clinical history would most likely indicate an acquired nail plate dystrophy on a thumb or the bilateral thumbs. Some reports have described an association of development of median canaliform dystrophy with trauma to the nail unit, but this is not a constant feature. The lesions are asymptomatic.
Characteristic findings on physical examination
Median canaliform dystrophy characteristically presents with a longitudinal groove in the central portion of the nail plate. This groove can begin at the proximal nail fold or slightly distal to it. Smaller grooves are noted connecting to the major longitudinal groove in an oblique fashion. This gives the overall appearance of an inverse “fir-tree” pattern within the nail plate. Generally, a thumb or the bilateral thumbs are affected. With more severe cases, the central longitudinal groove can become deep enough to cause a longitudinal split in the nail plate. The lunula of affected nails can be enlarged and show redness (Figure 1).
Expected results of diagnostic studies
Generally, diagnostic studies are not performed if the diagnosis is certain. Specific histopathologic features for this disorder have not been described. It is always a good idea to exclude a fungal infection in nails which are dystrophic, so a nail clipping sent for histology could be considered if the diagnosis is in question.
The main differential diagnosis for this disorder is the habit tic deformity. Similar to median canaliform dystrophy, the habit tic deformity is most often located on a thumb or bilateral thumbs. However, the pattern of dystrophy within the nail plate with a habit tic deformity is that of parallel transverse grooves, without a distinctive central longitudinal groove. The habit tic deformity is caused by trauma to the proximal nail fold by a repeated rubbing motion of the second digit on it.
With a habit tic deformity, a definite history of trauma can often be elicited from the patient. Also, because of the relationship of trauma to the development and persistence of a habit tic deformity, often damage to the proximal nail fold and cuticle can be identified on physical examination. As with median canaliform dystrophy, the lunula of affected nails can show enlargement and redness.
A lesion in the matrix causing a longitudinal split of the nail plate could be considered in the differential diagnosis of median canaliform dystrophy. A case was reported that describes a glomus tumor causing longitudinal splitting of the nail plate, which mimicked median canaliform dystrophy. A median nail dystrophy limited to the thumbs has recently been described in the “PDA nail,” and it would be reasonable to question the patient about frequent use of a personal digital assistant device.
Who is at Risk for Developing this Disease?
Median canaliform dystrophy is not associated with any clear-cut risk factors. However, a few cases have been described where median canaliform dystrophy occurred in association with isotretinion use, and resolved after the discontinuation of this medication. Rare familial cases of median canaliform dystrophy have been described.
What is the Cause of the Disease?
The etiology and pathophysiology of median canaliform dystrophy has not been defined pathologically. Given that the defect appears to be focused within the nail plate, median canaliform distrophy may be related to transient and localized physiologic alterations within the nail matrix epitheium.
Systemic Implications and Complications
Median canaliform dystrophy is not associated with systemic disease.
Reported therapies include clipping the nail plate short, smoothing the nail plate by buffing, preventing the nail plate from catching by covering it with tape or nail wrap. If associated with isotretinoin use, discontinuation of this medication has resulted in improvement. Occasionally, median canaliform dystrophy has resolved spontaneously, but can recur.
Optimal Therapeutic Approach for this Disease
Median canaliform dystrophy does not cause a functional impairment, and accordingly, treatment should be conservative. Most patients will do well with no therapy, or conservative interventions as listed above.
Once diagnosed, median canaliform dystrophy does not require additional monitoring or follow-up visits if it is a stable problem.
Unusual Clinical Scenarios to Consider in Patient Management
An unsual scenario would include a lesion in the matrix causing a longitudinal split in the nail plate mimicking median canaliform dystrophy. This has been reported with a glomus tumor. Additional evaluation and diagnostic testing, which could include a nail unit biopsy or imaging of the nail unit with magnetic resonance imaging (MRI), should be pursued if the nail dystrophy is associated with symptoms, or if the lesion is progressive.
Familial cases of median canaliform dystrophy have been reported, so asking patients about similar nail findings in other family members is an important part of the evaluation.
What is the Evidence?
Sweeny, S, Cohen, P, Schulze, K, Nelson, B. “Familial median canaliform nail dystrophy”. Cutis. vol. 75. 2005. pp. 161-5. (This article describes a familial variant of median canaliform dystrophy, where two brothers and their mother were affected.)
Olszewska, M, Wu, J, Slowinska, M, Rudnicka, L. “The ‘PDA Nail’”. Am J Clin Dermatol. vol. 10. 2009. pp. 193-6. (This article describes a median nail plate dystrophy of the thumbs noticed in two individuals associated with use of a personal digital assistant device. The nail changes improved with decreased use of the personal digital assistant. The changes described are similar to those seen with median canaliform dystrophy, so it is prudent to ask patients with thumbnail median nail abormalities about the extent of PDA use.)
Verma, S. “Glomus tumor-induced longitudinal splitting of the nail mimicking median canaliform dystrophy”. Indian J Dermatol Venerol Leprol. vol. 74. 2008. pp. 257-9. (A patient is described who presented with a longitudinal splitting of the thumbnail that appeared similar to median canaliform dystrophy. An associated glomus tumor was diagnosed on biopsy. Glomus tumor should be considered as a cause of nail dystrophy when associated with pain, especially when exacerbated by pressure or cold.)
Dharmagunawardena, B, Charles-Holmes, R. “Median canaliform dystrophy following isotretinoin therapy”. Br J Dermatol. 1997. pp. 658-9. (A patient with acne vulgaris was taking isotretinoin and developed median canaliform dystrophy on the bilateral thumbs 4 weeks after beginning this therapy. The nail changes resolved after completion of therapy.)
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