Keys To Managing Severe Onychomycosis

Myron Bodman, DPM

   One can determine the Onychomycosis Severity Index score by multiplying the score for the area of involvement (range, 0-5) by the score for the proximity of disease to the matrix (range, 1-5). Add 10 points for the presence of a longitudinal streak or a patch (dermatophytoma) or for greater than 2 mm of subungual hyperkeratosis. Mild onychomycosis corresponds to a score of 1 through 5, moderate onychomycosis would have a score of 6 through 15 and severe onychomycosis would range between 16 and 35.11

   Most importantly, the Onychomycosis Severity Index criteria have been validated.11 Using the Onychomycosis Severity Index scoring system, clinicians are likely to determine the same severity score given the same patient. This methodology is particularly important in diseases like onychomycosis in which there is a wide degree of severity among individual patients.

   It also helps to quantify the varying difficulties of clearing cases with nail root involvement or when the nail plate is thicker. For example, one can easily clear white superficial onychomycosis with topical medications and simple debridement while total dystrophic onychomycosis seldom clears without oral therapy.

   Severity indices are more economical and better benchmarks to monitor treatment progress rather than expensive mycological tests or just proximal clear zones. The Onychomycosis Severity Index numerically estimates the severity factors that limit the potential for clearing. Using this validated method, we can define cases of severe onychomycosis as those with scores from 16 through 35.

   Schemer states that the evaluation of the outcome of clinical cure, mycological cure and total cure should be based on the well-defined worldwide criteria.12 Otherwise, a comparison of results is impossible due to a lack of uniformity in different studies.

What You Should Know About Diagnostic Testing

Diagnostic testing has evolved over time. It used to be that we could culture suspected cases of onychomycosis with dermatophyte test media, incubate the specimens in desk drawers and speciate the results using a color chart. Interpretation could be difficult with many phenotypic variations. No two fungi look exactly alike. The KOH wet mount preparation of subungual debris is not a very sensitive method and clinicians seldom perform it on nail specimens.13

   Currently, the most sensitive test is a pathologist read biopsy of nail clippings stained with periodic acid Schiff (PAS) and or Grocott’s methenamine silver. A mycologist interprets fungal culture testing, which is very specific but not as sensitive as PAS. Fungal cultures are relatively slow growing, adding weeks and more cost to the workup. Fungal culturing is appropriate for atypical cases or when one suspects primary saprophytic infections. In that case, it is recommended that two subsequent cultures of the same saprophytic mold be in evidence before concluding that the saprophyte is the primary pathogen and not a contaminant.

   A new development has demonstrated the usefulness of dermoscopy in clinical differentiation of onychomycosis from common nail dystrophies. Piraccini and colleagues observed a characteristic of jagged proximal edges with spikes and longitudinal striations in patients with culture-proven onychomycosis while mycologically negative cases of traumatic onycholysis all have linear transverse edges without spikes.14 A dermatoscope is basically a handheld 10X polarized magnifying lens illuminated with 11 small halogen lamps. It allows the examiner to easily look through a translucent nail plate and visualize the nail bed directly.

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