INTRODUCTION
Onychomycosis is the most common nail disease in adults, representing up to 50% of all nail disorders, nearly always being associated with tinea pedis.1-3 Epidemiologic
data indicate a prevalence of 13.8% in the United States,4 with a number of factors contributing to an increasing incidence.5 Onychomycosis is more common in males than females, in people with human immunodeficiency virus, with diabetes, and with increasing age.6 Other predisposing factors include immunosuppression, peripheral arterial disease, sports activities, and pre-existing dystrophic nails from a variety of causes including psoriasis and trauma.7
With appropriate treatment, in many individuals the normal clinical appearance of the nails can be restored over time. However,
sustained and complete cure rates can be disappointing,8 slow to achieve, and with disease relapse seen frequently.9 Indeed,
these factors present some of the biggest challenges in the management of the disease.
It would be valuable to identify patients who are likely to fail treatment so that alternative and individualized treatment regimens can be formulated. Conversely, identifying those patients who are more likely to achieve a total cure would be helpful to maintain patient motivation with a treatment lasting many months.
Several factors influence the likelihood of treatment success: clinical subtype of onychomycosis, age, and peripheral vascular
disease; and the speed of nail growth, extent of nail involvement, increased number of nails involved, and presence of a dermatophytoma have all been suggested to influence treatment efficacy.10,11 Patients with matrix or lateral nail plate involvement, slow nail growth, or a dermatophytoma are less likely to reach complete cure.10 Patients exhibiting a faster nail outgrowth are likely to show better treatment response;12,13 although
not all studies have found a link between rate of nail growth and treatment cure.14 The presence of a dermatophytoma
has often been suggested to negatively affect cure, but definitive statistical support is lacking.12,15,16 In general, there are no widely accepted prognostic factors that have been proven and replicated, with significant disagreement between different studies performed.
Reasons for treatment failure are not always clear cut. There is little evidence that treatment failures can be identified on the basis of clinical presenting features or progress during treatment.
A study of 496 patients examined the influence of age, gender, and extent of disease, previous treatment, and duration of infection, and was unable to identify any predictive factors; although having a positive mycology 12 weeks into treatment was associated with treatment failure.17
