Chronic fungal infection of the nail beds. Culture scrapping or nail clippings.
Topical therapy from NEJM (PubMed):
Nail- For superficial white onychomycosis or fungal infection limited to the distal third; continued until there is no evidence of residual viable fungus, use Amorolfine 5% lacquer (Loceryl and Curanail, not available in the United States) once or twice a week for 6 to 12 months OR Ciclopirox olamine 8% lacquer (Penlac) daily for 48 weeks OR Tioconazole 28% paint (not available in the United States) twice daily for 6 to 12 months.
Onychomycosis: terbinafine 250 mg po qd for 6 weeks.
Toenails: terbinafine 250 mg po qd x 12 weeks OR itraconazole 400 mg/day po q week each month for 2-4 months OR fluconazole 200 mg po q wk x 12-24 weeks. A meta-analysis suggests terbinafine is more better than intermittent itraconazole for mycological cure of toenail onychomycosis (PubMed).
I think the risks of drug toxicity (mostly hepatitis) and cost make treatment silly unless your patient is a professional hand or foot model.
ICD9 Codes (Soon to be supplanted by ICD10)
Onychomycosis 110.1; finger or toe 110.1