Reflectance confocal microscopy as a new diagnostic tool in transformed mycosis fungoides.

Patients with mycosis fungoides typically experience an indolent disease. In some cases, the disease undergoes a process of large cell transformation which often heralds a more aggressive course with shortened overall survival. In order to rule out large cell transformation, biopsy specimens are often collected from patients with established disease who develop new papules, plaques or tumours. In some cases, multiple biopsies are needed and scar, infection and sampling error can occur. Our aim was to evaluate lesions suggestive of large cell transformation using in vivo reflectance confocal microscopy and to correlate confocal features with histopathologic findings in three patients with biopsy-proven mycosis fungoides who developed new lesions during follow-up. A total of six lesions, two lesions per patient, were examined. Reflectance confocal microscopy demonstrated large bright roundish pleomorphic cells in the epidermis, dermoepidermal junction, dermis and hair follicle in 5 of 6 lesions. The same 5 lesions were confirmed as large cell transformation by histopathology. Dermoepidermal junction obscuration, Pautrier microabscesses, epidermal disarray, spongiosis and dendritic cells were also detected by reflectance confocal microscopy and correlated to histopathology. In conclusion, reflectance confocal microscopy is useful in identifying large cell transformation within mycosis fungoides lesions. Reflectance confocal microscopy can therefore be of value in targeting the biopsy site, thereby reducing the chance of a false-negative histopathological finding.