The five microscopy-negative, PCR-positive specimens involved made up 36% of the 14
specimens in our study that would have been considered completely negative for mycotic agents in conventional studies. All
five of these cases involved T. rubrum as the etiologic agent.
(An alternative scenario, that the T. rubrum amplified in these
five cases came from nearby infected skin rather than the nails
themselves, seems highly unlikely, given the onychomycotic
symptomatology of the nails combined with the likelihood that
any dermatophytosis of skin adjacent to the nails would probably also affect the nails. Also, infections of more distant areas
such as toe webs would probably not yield sufficient contaminating material to cause false positives in nail PCR, given the
normal dermatological practice of cleaning away the contaminated superficial surface of infected nails before submitting a
sample to the laboratory.) In all other cases in which a known
or suggestive etiologic agent was detected by PCR alone, the
presence of fungal filaments in direct microscopy would have
indicated at least that a mycosis was present. The five microscopy-negative, PCR-positive cases, though, mean that PCR
increased the number of confirmed mycoses in this study from
181, as would have been recognized in conventional studies, to
186, an increase of 2.8%. Though this may not seem a high
percentage, the high numbers of patients seeking relief from
onychomycosis must be kept in mind. Scher (43) showed that
in one year alone, 662,000 Americans over the age of 65 consulted a physician for handling of suspected onychomycosis. If
2.8% of this population were to have their mycosis missed on
the first examination, this would amount to 18,536 inade quately handled patients over 1 year in just that single demographic group.