White Streaks: Dermoscopic Sign of Distal Lateral Subungual Onychomycosis.

Sir,

Distal lateral onychomycosis sometimes poses difficulties in diagnosis. It is difficult to differentiate it from distal lateral onycholysis seen in psoriasis. The fact that potassium hydroxide mount and fungal culture have low sensitivity in detecting onychomycosis makes it imperative to search for other diagnostic tools which may help in distinguishing the two conditions.[1] We have explored the use of dermoscope to help combat this difficulty.

We studied 36 patients of onychomycosis disease with duration ranging from 6 months to 2 years. Diagnosis was proven by potassium hydroxide mount, and then the patient was enrolled in the study. The history and clinical examination of the patient was taken after obtaining consent from the patient. Examination of the nail was done using a contact dermoscope (Heine's delta 20) and a video dermoscope. Oily medium like liquid paraffin or gel was used for the interface in case of a contact dermoscope. Video dermoscope of the type ultracam TLS manufactured by dermaindia was used. Clinical photographs of the nails were taken using canon PowerShot G12 camera. The nails were examined by the video dermoscope on white light and polarized light.

Out of the 36 patients evaluated, 21 had distal lateral subungual onychomycosis. All these patients showed white, irregular streaks demarcating the area of onychomycosis with the normal nail Figures 1 and 2. The streaks were sharp and distinct and were present throughout the entire length of the involved area. These streaks are projected toward the normal part of the nail. We compared this finding with 10 patients of psoriasis having distal lateral onycholysis. On dermoscopy, these patients showed an ill-defined area of reddish orange discoloration at the affected portion of the nail. There were no well demarcated white streaks in these cases of psoriasis as seen in patients of onychomycosis. Other findings included chromonychia (discoloration of the nail plate) seen in 13 patients. Two of these patients showed growth of nondermatophytic molds (Candida and Aspergillus) on culture. Subungual hyperkeratosis was seen in 7 patients. Both chromonychia and hyperkeratosis were statistically significant (P < 0.05).

Figure 1

Jagged and well demarcated white line separating the affected distal part of the nail from the normal region

Figure 2

White well demarcated discoloration of distal lateral subungual onychomycosis

Distal lateral onychomycosis is the most common form of onychomycosis with a prevalence of around 62%.[2] Distal onychomycosis has been described in the literature as being well demarcated, jagged edges. Also, white yellow longitudinal striae are seen at the affected portion of the nail. In our study, the dermoscopic finding of sharp demarcation between the affected and the normal nail was consistently observed.[3] Nakamura and Costa too have described opacity with distal streaks in onychomycosis.[4] Piraccini et al. too observed a sharp jagged edge of the proximal end and compared it with traumatic onycholysis. It was observed that traumatic onycholysis had a linear edge without the sharp spiked border.[5] De Crignis et al. have studied the dermoscopy of onychomycosis in 502 patients. The features of distal lateral onychomycosis described were sharp longitudinal white striae. They have postulated to be a result of the direction of the fungal invasion. It occurs from the distal aspect and extends proximally in an irregular, albeit sharply defined manner. They have also used dermoscopy as a tool for presumptive diagnosis and then, confirmed the diagnosis by direct microscopy and culture in 10 patients.[6]

To summarize, in our study, longitudinal striae and jagged spikes were the most common features seen. Other additional features were subungual hyperkeratosis and chromonychia.

This feature can help in diagnosing onychomycosis in cases of strong clinical suspicion but with negative laboratory results.

To conclude, dermoscope, which is a handy tool in our day to day practice can aid in the diagnosis of onychomycosis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.