DES and primary progressive multiple sclerosis: In our case, although the characteristics of immunostaining, morphological features, and gene fusion were enough to reach the diagnosis of PPMS while ruling out other tumors as differentials, the strong positivity for desmin was atypical.3) In the conventional literature, desmin, a protein that constitutes the cytoskeleton of myocytes, is usually negative in PPMS, while a higher percentage is positive in AFH, where myeloid stroma is considered a morphologic feature.