Shiho Ooka

A case of black dot ringworm with a review of Japanese cases.

Black dot ringworm (BDR), caused by Trichophyton violaceum var. glabrum (T. glabrum), was observed in a 28‐year‐old Japanese female who had been treated with prednisolone (22.5 mg/day) for systemic lupus erythematosus. It was successfully treated with oral terbinafine (125 mg/day) for 12 weeks. The causative fungus was identified by molecular analysis as well as morphological and biochemical examination. The chitin synthase 1 (CHS1) gene cleavage pattern of the clinical isolate with restricted enzyme HinfI was identical to that of T. violaceum. We reviewed previous reports of BDR to determine the historical trend of this infection in Japan. Since 1974, 93 Japanese cases have been reported. The age distribution was bi‐modal: the higher peak consisted of children (aged 0–15 years), and the lower peak was composed of the elderly (aged 60–75 years). In the elderly group, females were predominant (M: F=1: 22, p<0.001). T. violaceum, including T. glabrum, was identified as the most common causative fungus of BDR (75.3%). Sixty percent of cases showed slight erythema. In 8 families, 16 cases were found to be intrafamilial infections. A history of previous steroid treatment was described in about 40%.

Molecular confirmation of a Trichophyton violaceum isolate from human black-dot ringworm.

A clinical isolate from a black-dot ringworm lesion of a 28-year-old female Japanese was investigated by morphological and biochemical analyses as well as molecular analyses. The isolate grew well onthiamine enriched agar and did not produce violetpigment, macroconidia or microconidia on Sabourauds dextrose agar. Approximately 620-bp genomic DNA fragments of the CHS1 gene were amplified from Trichophyton mentagrophytes, T. rubrum, T. tonsurans and T. violaceum by polymerase chain reaction (PCR) and sequenced. The chitin synthase 1 (CHS1) nucleotide sequences of the clinical isolate showed more than 97% similarity to that of T. violaceum and less than 96% similarity to that of T. mentagrophytes, T. rubrum and T. tonsurans. The phylogenetic analysis of their sequences revealed that the clinical isolate was genetically close to T. violaceum and distinct from T. mentagrophytes, T. rubrum and T. tonsurans. Therefore, the isolate was confirmed as T. violaceum by mycological examination and molecular analyses.