Diagnosis of Onychomycosis

Onychomycosis (OM) can be identified by its appearance. However, other conditions and infections can cause problems in the nails that look like onychomycosis. OM must be confirmed by laboratory tests before beginning treatment, because treatment is long, expensive, and does have some risks.

• A sample of the nail can be examined under a microscope to detect fungi. See Anatomy of the Nail for information on the parts of the nail.



• The nails must be clipped and cleaned with an alcohol swab to remove bacteria and dirt.



• If the doctor suspects distal lateral subungual onychomycosis (DLSO), a sample (specimen) should be taken from the nail bed to be examined. The sample should be taken from a site closest to the cuticle, where the concentration of fungi is the greatest.



• If proximal subungual onychomycosis (PSO) is suspected, the sample is taken from the underlying nail bed close to the lunula.



• A piece of the nail surface is taken for examination if white superficial onychomycosis (WSO) is suspected.



• To detect candidal onychomycosis, the doctor should take a sample from the affected nail bed edges closest to the cuticle and sides of the nail.



• In the laboratory, the sample may be treated with a solution made from 20% potassium hydroxide (KOH) in dimethyl sulfoxide (DMSO) to rule out the presence of fungi. The specimen may also be treated with dyes (a process called staining) to make it easier to see the fungi through the microscope.



• If fungi are present in the infected nail, they can be seen through a microscope, but the exact type (species) cannot be determined by simply looking through a microscope. To identify what exactly is causing onychomycosis, a technique called culturing is used. Using a fungal culture to identify the particular fungus is important because regular therapy may not work on nondermatophyte molds.
  
  
  • The infected nail is scraped or clipped.
  
  
  
  • The scrapings or clippings are crushed and put into containers. Any fungus in the samples can grow in the laboratory in these special containers.
  
  
  
  • The species of fungus can be identified from the cultures grown in the lab.