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If fingernails are abnormal but toenails are normal, the diagnosis is not likely to be onychomycosis. An exception to this rule, however, is in cases of Candida onycholysis, which are more common in women and among those with Raynaud's syndrome.
When a patient shows up with what is suspected to be a fungal disease of the nails, some key indicators can suggest the likelihood of onychomycosis, or rule it out, says Dr. Elewski, a professor of dermatology at the University of Alabama.
Causes of fungal infections include dermatophytes, Candida and some non-dermatophyte molds. Another clinical pearl Dr. Elewski offers is that if fingernails are abnormal but toenails are normal, the diagnosis is not likely to be onychomycosis. An exception to this rule, however, is in cases of Candida onycholysis, which are more common in women and among those with Raynaud's syndrome.
"Candida responds nicely to oral fluconazole," Dr. Elewski tells Dermatology Times. "A dose of 200 mg administered once weekly for four to eight weeks is generally sufficient for most patients."
To confirm a diagnosis of onychomycosis, a KOH (potassium hydroxide) test is considered the best method. The test involves placing the specimen on a slide with one drop of 10 percent to 20 percent KOH solution. Stain such as chlorazol black E (specific for chitin) can be added to accentuate hyphae. Wait several minutes and examine the results under a microscope on low power with reduced light.
Other alternatives for diagnosis include taking a culture or conducting a nail biopsy, but a problem with taking a culture of nails is the fact that growth recovery rate is only 40 percent to 60 percent. Furthermore, a pathogen cannot be identified in 40 percent to 60 percent of patients.
"If an initial KOH is negative, clinicians may want to culture for dermatophyte, and if that is positive, the patient indeed has onychomycosis," Dr. Elewski says.
Consider treatment options
Treatment of onychomycosis is complicated due to potential drug interactions, and labeling changes are in fact in store for both terbinafine and itraconazole to read "recommended healthcare professionals should obtain nail specimens for lab testing prior to prescribing the medications for onychomycosis, to confirm the diagnosis."
Itraconazole has the potential to cause serious interactions with certain drugs, and its absolute contraindications include:
Itraconazole has also been associated with congestive heart failure, and a study linking the drug to 13 deaths (Lancet 2001;357:1766-1767) resulted in a "black box" warning that the drug should not be administered to patients with evidence of ventricular dysfunction such as CHF.
Terbinafine, however, has no contraindications to concomitant drug use, and in treating onychomycosis, a therapy of 250 milligrams of oral terbinafine daily for three months should be sufficient for some patients, Dr. Elewski says. If, however, there is severe infection, white or yellow "spikes" or lateral nail involvement, treatment for four months or longer may be necessary.
Disclosure: Dr. Elewski is a consultant and clinical investigator for Novartis.