Onychomycosis is a fungal infection of the nails that causes discoloration, thickening, and separation from the nail bed. Onychomycosis occurs in 10% of the general population, 30% of persons older than 60 years, and 50% of those older than 70 years.

Onychomychosis

Onychomycosis in people with diabetes is more than a cosmetic nuisance; it increases the risk for other foot disorders and limb amputation.^4,10-22 The outcome of not treating onychomycosis in diabetic patients can be worse than in those without diabetes. Thus, effective treatment in these patients is of paramount importance.¹³ Because onychomycosis in diabetic patients can lead to many complications, most insurance companies cover treatment in documented cases. Thickened, dystrophic nails can be very painful and make walking difficult. Injury to adjacent skin from mycotic nails may occur without patients' awareness and can lead to secondary infections, both fungal and bacterial, including paronychia and cellulitis.^3,4,9,14,15 Thickened nails can cause erosions of the nail bed and hyponychium because of pressure, just as tight shoes can cause friction blisters in these patients. When combined with peripheral neuropathy, blisters and erosions may progress to cellulitis or osteomyelitis of the underlying bone.^3,4,14,15 Extension of the fungal infection to surrounding skin causes tinea pedis, which may lead to fissures in the plantar and interdigital skin. These may also provide a route for the entry of bacteria.¹⁵

Patients with diabetes-related comorbidities are at especially increased risk for morbidity in onychomycosis. Diabetic patients suffering from decreased foot sensation are more prone to trauma, which damages the nail and nail matrix, opening portals of entry for the fungus to infect the nail.^13,15 Some diabetic patients can be obese, which may make the act of bending over to examine their feet difficult.¹⁵ Diabetic patients with cataracts¹⁶ or retinopathy¹⁵ may be unable to properly examine their feet regularly. Retinopathy has been found to be an independent risk factor for onychomycosis in diabetes.⁹ Other risk factors include peripheral neuropathy,^3,9,15 impaired peripheral circulation,^4,9 age,^4,9 family history,⁴ and intake of immunosuppressant drugs.⁴ In addition, the duration of diabetes is correlated with severity of onychomycosis when present.⁴ Male diabetic patients have three times higher risk of onychomycosis than female diabetic patients.⁴

The presence of fungal infection in the nails increases the risk of other infections of the foot and leg. In one study, diabetic patients with onychomycosis had a 15% rate of secondary infections compared with a 6% rate of secondary infections in diabetic patients without onychomycosis. Additionally, diabetic patients with onychomycosis had an approximately three times greater risk of gangrene or foot ulcer compared with diabetic patients without it.¹⁰ The total annual costs for toe, leg, and foot amputations in the United States in 2003 were almost $2 billion.¹⁷ These costs covered 112,551 total amputations, with an average cost of $16,826 for each procedure.¹⁷ In 2001, the total cost of amputations in diabetic patients was > $1.6 billion.¹⁸ The majority of lower-limb amputations occur in diabetic patients.¹⁹

Because the risk of amputation increases with onychomycosis, it is imperative for clinicians to examine diabetic patients' feet and when suspicious, obtain a sample for diagnosis.

Clinical Diabetes 2006;24(4):160–166