When A Patient Has A Discolored Onychomycotic Toenail

Author(s): 
Henry J. Carson, MD, and Eugene Nassif, DPM

   While research has shown that onychomycosis is more common in patients with diabetes, we need to be cognizant of different etiologies and perhaps reexamine those when an initial treatment course fails to get results.1

   A 36-year-old woman presented with a six-month history of a discolored toenail of the right great toe.

   She was a moderately overweight Caucasian woman with a 20-year history of juvenile-onset diabetes mellitus. She had poor to moderate control of her disease.

   She never suffered serious episodes of diabetic ketoacidosis as a result of her diabetes and had not previously experienced opportunistic infections. Her overall health had been good. She had no occupational or domestic exposure to soil, pigeons, decaying grass or leaf mold. She had no history of travel.

   The physical examination confirmed an abnormal, geographic, uniform yellow-tan demarcated area of discoloration in the nail. There was no evidence of thickening, dystrophy, flaking or brittleness. The discoloration of the nail was distinct in comparison to the other toenails. We presumptively diagnosed and treated it as onychomycosis.

   The patient underwent treatment with 250 mg of oral terbinafine hydrochloride (Lamisil, Novartis) daily for 12 weeks. On follow-up at six and 18 weeks, there was no effect on the discolored area of the nail although it had grown out sufficiently to permit us to send nail clippings for cultures.

What You Should Know About Rhizopus Onychomycosis

   The laboratory prepared and cultured the nail clippings on Sabouraud agar. The fungus was a rapidly growing pathogen with mycelia, pigmented rhizoids and grooved sporangiospores. The fungus assimilated ethanol, glycerol and adonitol but not lactose or nitrate. These findings were consistent with Rhizopus species.

   Rhizopus ssp. are opportunistic fungi that sometimes colonize the oropharyngeal cavities and sinuses of healthy individuals.2 In immunosuppressed people or those with chronic diseases such as cancer or diabetes, disease due to Rhizopus may occur.2,3 Percutaneous introduction of Rhizopus spores into wound sites may cause extra-oropharyngeal infection or infection by direct contact with the fungus in the soil may occur.2,4,5

   Rhizopus ssp. has worldwide distribution.2 While it is commonly found in soil, it can have other ecological niches including fresh fruits such as strawberries or pigeon droppings.6,7 Rhizopus can be a normal commensal in the sinuses and is rarely pathogenic. Due to its nonpathogenic presence in the sinuses, disease due to Rhizopus is most commonly rhinocerebral, orbital or pulmonary.2,8,9 Researchers have also identified Rhizopus ssp. postoperatively in patients who have undergone sternotomy, those on peritoneal dialysis, patients with leukemia/lymphoma, patients with other cancers, those who have had organ transplant procedures and in those with systemic lupus erythematosus.3,10,11

   Rhizopus is rarely pathogenic except in settings of immunosuppression or, as in this patient, in people with diabetes and episodes of hyperglycemia. The significant risk of Rhizopus infection is its angioinvasive tendency, which can lead to thrombosis and necrosis. Sites of infection other than the sinuses and lungs can be due to percutaneous introduction of spores from injuries. When there is systemic involvement, treatment with amphotericin B is indicated.2

   Tinea ungium or onychomycosis is typically caused by dermatophytes such as Trichophyton or Microsporum ssp.12,13 Researchers have recognized a wider range of fungal infections of the toenails including common fungi such as Candida or Aspergillus or exotic species such as Scytalidium and Acremonium.12-14 Often the causal agent of onychomycosis is based on geography. Infection of the feet or toenails by Rhizopus has been identified mostly in the developing world or Mideast.4,5

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