A relatively easy in-office test is able to help the family doctor or podiatrist confirm if a fungus is causing the signs and symptoms of the nail disease known as onychomycosis. At about $1 a test, it can replace the $25 central lab tests usually employed, and the result is available within 2 weeks, too!

Ugly Toenail - Is it Onychomycosis?

Summarized by Robert W. Griffith, MD
March 21, 2003

Introduction

It's said that, by the age of 50, one in two people have at least one toenail that's thickened, yellowed, and disfigured; the likely cause is a treatable fungal infection called onychomycosis. Sufferers of this disease have their own society and regular newsletter (see the first link below).

There are good oral and local medications for treating onychomycosis, but it's important that the diagnosis is confirmed, as far as possible, early in the course of treatment. Other conditions that may look like onychomycosis include psoriasis of the nails, injury of the nailbed leading to deformity (onychogryphosis), contact irritants, bacterial infections, and even tumors.

Usually, scrapings of tissue from under the nail are sent off to a laboratory for microscopy and culture for fungi. The report normally takes 4-6 weeks, and in the meantime, if the clinical signs are clear-cut, the patient is treated with an antifungal drug. Now a new in-office technique offers the possibility of a shorter, less complicated way of confirming the diagnosis of onychomycosis. It's been tested to see if it's as reliable as the typical way.

Testing the new diagnostic test

The new test system is an in-office culture using a special dermatophyte test medium (DTM) culture. This medium (a specially enriched sort of jelly that encourages fungal growth) changes color from yellow to red if a nail fungus is growing; this usually occurs within 3 to 7 days.

Family doctors and podiatrists throughout the USA enrolled 670 patients with the signs and symptoms of onychomycosis. At each patient's first visit a scraping was taken from the toenail bed, and divided into two parts; one part was cultured in the doctor's office using DTM, and the other was sent to a central reference laboratory (the University of Texas Fungus Testing Laboratory, San Antonio), for expert workup. The doctors and podiatrists were given a videotape showing how to obtain the nail-bed sample and how to inoculate the DTM culture tube. The tube was kept at room temperature for up to 2 weeks, with the tube color checked daily.

Eighty podiatrists and 69 primary care physicians entered a total of 670 patients into the study. There were roughly equal numbers of men and women. 45% of the participants were over 65, and 17% were diabetic.

The central lab cultures were positive in 44% of the participants, while the in-office DTM cultures were positive in 51%. The results of both sorts of test were in agreement - both positive in 206, both negative in 214 - in 68% of the patients. This provided evidence of a significant degree of agreement between the two test systems.

It was found that skin fungi (dermatophytes) were the main cause of onychomycosis, accounting for over 90% of these infections. Men were more likely to have positive results by both culture methods tested.

What does this mean?

This study has confirmed that skin fungi are the main cause of onychomycosis symptoms. Cultures of fungi were positive in 44% of the patients using the central lab method, and in 51% using the in-office DTM method. The approximate cost of the latter is quoted as $1 per test, compared with $25 for the central lab. It's also important that confirmatory results are obtained much more quickly with DTM - less than 2 weeks, compared with 4-6 weeks for the central lab method.

This study shows that primary care physicians and podiatrists can set up an in-office DTM culture and starting antifungal therapy in patients with clinical signs and symptoms of onychomycosis. A negative read-out at 2 weeks would mean re-evaluation of the patient - to see if treatment has proved effective, whether the diagnosis is correct, etc; nothing has been lost by not requesting a central lab work-up at the first visit, and considerable money and time may have been saved.

Source

• Office practice-based confirmation of onychomycosis. BE. Elewski, J. Leyden, MG. Rinaldi,  et al., Arch Intern Med, 2002, vol. 162, pp. 2133--2138

Related Links
National Onychomycosis Society
Online Atlas of Dermatology: Onychomycosis
Integrative Medicine: Nail Disorders
Tip of the Month #3: How To Look After Your Feet