Microsporum spp. onychomycosis: disease presentation, risk factors and treatment responses in an urban population()

BACKGROUND: Dermatophytes are the main causative agent of all onychomycosis, but genus Microsporum is infrequent and the risk of acquiring the infection is often associated with exposure to risk factors. OBJECTIVES: To describe clinical characteristics of onychomycosis due to Microsporum onychomycosis in an urban population. METHODS: This was a retrospective analysis of the epidemiological and clinical features of 18 Microsporum onychomycosis cases of a total of 4220 of onychomycosis cases diagnosed between May 2008 and September 2011 at the tertiary referral center for mycology in Guatemala. RESULTS: Eighteen cases of Microsporum onychomycosis (M. canis, n = 10; M. gypseum, n = 7; M. nanum, n = 1) were identified (prevalence = 0.43%). Infection was limited to nails only and disease duration ranged from 1 month to 20 years (mean = 6.55 years). The toenails were affected in all cases except for a single M. gypseum case of fingernail. The most common clinical presentation was distal lateral subungual onychomycosis (12/18) followed by total dystrophic onychomycosis (5/18), and superficial white onychomycosis (1/18). M. gypseum presented in 6 cases as distal lateral subungual onychomycosis and in 1 case like total dystrophic onychomycosis. Five cases (27.78%) were associated with hypertension, diabetes, and psoriasis. Treatment with terbinafine or itraconazole was effective. Two cases of M. canis distal lateral subungual onychomycosis responded to photodynamic therapy. CONCLUSION: This is the largest reported series of Microsporum onychomycosis and demonstrates such a disease in an urban population. In 27.78% of the cases risk factors for infection were associated to comorbid states. We also report the first 2 cases of successfully treated M. canis onychomycosis with photodynamic therapy and a rare case of M. canis associated dermatophytoma.