Abstract:

Objective To assess the clinical features and diagnostic index of progressive macular hypomelanosis （PMH）. Methods Eight patients with PMH were recruited into this study. Wood′s lamp and in vivo confocal laser scanning microscopy （CLSM） were utilized to observe the lesions of all patients. Microbiological culture of lesion specimens from 2 patients was performed. Tissue specimens from 4 patients underwent immunohistochemical staining with anti-S-100 and anti-TRP-1 antibodies for the detection of melanocyte quantity. Electron microscopy was utilized to observe ultrastructural features of lesions. Primary culture of melanocytes was carried out with lesional epidermis. Results Under Wood′s lamp, the lesions of PMH showed punctiform red fluorescence. CLSM revealed complete pigmented rings in lesions with decreased melanin granules compared with those surrounding normal skin. Microbiological culture grew red fluorescence-producing, gram-positive bacillus which was identified as Propionibacterium acnes. Immunohistochemistry showed no significant difference in the number of S-100-postive cells or TRP-1-positive cells per high power field （× 400） between lesions and surrounding normal skin （8.25 ± 0.96 vs 8.75 ± 1.71, 4.25 ± 0.96 vs 4.50 ± 1.29, both P > 0.05）. Ultrastructural studies showed a large reduction in the number of type Ⅳ melanosomes in lesions of PMH, along with numerous membrane bound bodies and clusteredly distributed, small type Ⅱ-Ⅳ melanosomes. Melanocytes, with morphological similarity to normal melanocytes, were successfully isolated from the lesional tissue, cultured and identified. Conclusion A primary diagnostic criteria is proposed for PMH according to the clinical and experimental studies.