T-cell clonality analysis in biopsy specimens from two different skin sites shows high specificity in the diagnosis of patients with suggested mycosis fungoides

BackgroundThe diagnosis of mycosis fungoides (MF) is often difficult because of significant clinical and histopathologic overlap with inflammatory dermatoses. T-cell receptor (TCR)γ chain rearrangement by polymerase chain reaction (PCR) (TCR-PCR) is a helpful adjuvant tool in this setting, but several of the inflammatory dermatoses in the differential diagnosis of MF may contain a clonal T-cell proliferation.ObjectiveWe examined whether analysis for T-cell clonality and comparison of the clones with the standardized BIOMED-2 PCR multiplex primers for the TCRγ chain from two anatomically distinct skin sites improves diagnostic accuracy.MethodsWe examined two biopsy specimens each from 10 patients with unequivocal MF, from 18 patients with inflammatory dermatoses, and from 18 patients who could initially not be definitively given a diagnosis based on clinical and histopathologic criteria.ResultsEight of 10 patients with unequivocal MF had an identical clone in both biopsy specimens. Two of 18 patients with inflammatory dermatoses were found to have a clone in one of the biopsy specimens. On further follow-up of the 18 patients with morphologically nondiagnostic biopsy specimens, 13 of 18 were later confirmed to have MF and 5 of 18 had inflammatory dermatoses. Eleven of 13 patients with MF had an identical clone in both biopsy specimens; two of 13 had a polyclonal amplification pattern in both biopsy specimens. Four of 5 patients with inflammatory dermatoses had no clone in either biopsy specimen. One patient with an inflammatory dermatosis had an identical clone in both specimens. The sensitivity of TCR-PCR analysis to evaluate for an identical clone at different anatomic skin sites (dual TCR-PCR) is 82.6% and the specificity is 95.7%.LimitationsThe number of patients in the study group was limited.ConclusionThese data suggest that dual TCR-PCR is a very promising technique with high specificity in distinguishing MF from inflammatory dermatoses.