Human myxovirus resistance protein 1 (MxA) as a useful marker in the differential diagnosis of subcutaneous lymphoma vs. lupus erythematosus profundus.

BACKGROUND

Substantial clinicohistologic overlap exists between lupus erythematosus profundus (LEP) and lymphomas involving the subcutis, including subcutaneous panniculitis-like T-cell lymphoma (SPTCL) and primary cutaneous gamma/delta T-cell lymphoma (GDTCL). Unequivocal markers separating the entities are not established.

OBJECTIVES

To explore the usefulness of interferon alpha (INF-α)-induced protein, myxovirus resistance protein 1 (MxA), in the differential diagnosis of these entities, as studies show that the expression pattern of MxA follows the distribution of the inflammatory infiltrate in cutaneous lupus, while INF- α is not known to operate in lymphoma.

MATERIALS AND METHODS

MxA immunohistochemistry was performed on skin biopsies from 5 patients with a clinical and histological diagnosis of SPTCL, 9 patients with GDTCL and 9 patients with LEP.

RESULTS

In SPTCL and GDTCL, MxA was primarily seen in macrophages and generally did not exceed 20% of the infiltrate. In contrast, a significant portion of the subcutaneous infiltrate was positive for MxA in LEP, with 50% of the infiltrate staining on average. A greater number of macrophages and lymphocytes stained with a greater intensity as well (P<0.001). Moreover, endothelial cell staining was uniquely identified in LEP but not in lymphoma.

CONCLUSION

Although specificity is not 100%, minimal staining of MxA is a predictor for SPTCL or GDTCL. Conversely, extensive staining for MxA both qualitatively and quantitatively is a feature of LEP. Endothelial staining also appears to be specific for LEP.