When A Patient Has A Discolored Onychomycotic Toenail
Treatment of onychomycosis is rarely successful with older antifungal regimens although fluconazole (Diflucan, Pfizer), itraconazole (Sporanox, Ortho McNeil) and terbinafine are usually effective with the dermatophytes.12,15 However, the present patient’s case demonstrates that newer medicines may not be effective with an exotic fungus.
The lack of fungal elements on histology was not unusual. It is not uncommon for the fungi not to be visible microscopically. This occurs in approximately 40 percent of culture-proven cases.15 The clinical appearance of the nail did not change in the course of treatment with terbinafine. This antifungal agent interferes with the enzyme squalene epoxidase to inhibit the formation of the fungus-associated lipid ergosterol. Loss of this cell membrane element is believed to cause increased fungal cell wall permeability and death. However, terbinafine is mostly effective in dermatophytes, of which Rhizopus is not a member.
Inside Insights On Treatment
Based on this experience, we recommend the following protocol for treatment of a patient with an unusual fungal infection of the toenail.
On the first clinical evaluation, collection of the patient’s medical history is useful to anticipate atypical microbiology results. Physical examination of the infected toenail should include documentation of unusual patterns, discoloration or growth of the suspected fungus. Nail clippings for culture are essential. One should initiate treatment with standard therapy but in the event that this fungus grows in culture, consider an alternative treatment.
We have found avulsion of the nail with careful follow-up to be effective. The angioinvasive properties of Rhizopus seen in other settings do not appear to be a risk factor with onychomycosis, possibly because the nail matrix denies the fungus access to a significant blood supply and is an anatomic barrier to dissemination. However, one should report to the primary caregiver the presence of an opportunistic fungus in an at-risk patient in case the presence of one opportunistic fungi connotes a level of disease or immunosuppression that may warrant additional monitoring of the patient.
The patient had an infectious disease consultation to evaluate the risk of angioinvasion or other systemic complication. Considering that the fungus was limited to one nail, the assessment was an anomalous localized fungal infection with mechanical barriers to systemic infection so it did not require systemic treatment. Accordingly, the physician handled her treatment as a podiatric procedure.
After we discussed the treatment options, the patient chose total avulsion of the nail with the anticipation that a new nail might be free of fungus. Accordingly, we anesthetized the right great toe with a digital block of 1% lidocaine, removed the nail and sent the specimen for histologic examination. The patient tolerated the procedure well.
After softening the nail in potassium hydroxide, we sectioned the nail and prepared histologic slides. The slides included routine hematoxylin and eosin as well as a Gomori methenamine silver stain, which characteristically stains fungal elements. Microscopic examination showed lamellar dystrophy but no evidence of fungi.
The patient received a prescription for econazole nitrate 1% applied topically twice daily. At two months, new nail was growing from the matrix. At five months, nail growth was normal without evidence of dystrophy or recurrent fungus.
Dr. Carson is a consultant at Foot and Ankle Specialists of Iowa in Cedar Rapids, Iowa.
Dr. Nassif is in private practice at Foot and Ankle Specialists of Iowa.
Dr. Morse is the President of the American Society of Podiatric Dermatology. He is a Fellow of the American College of Foot and Ankle Surgeons, and the American College of Foot and Ankle Orthopedics and Medicine. Dr. Morse is board certified in foot surgery.