Dermatomyositis (DM) is an idiopathic autoimmune myopathy characterized by muscle weakness and purple-pigmented rashes. Approximately 15% to 30% of DM cases are associated with an underlying malignancy, typically lung and ovarian cancers, but some hematologic malignancies, including primary myelofibrosis have been reported.
In a case study published in Case Reports in Hematology, investigators report on the first known case of DM associated with secondary myelofibrosis (MF) following polycythemia vera (PV).
The study follows a 69-year-old male patient with a 15-year history of PV, a disorder of the bone marrow that causes the overproduction of red blood cells. The patient reported increasing weakness in his upper and lower extremities without pain over the course of 4 days, in addition to difficulty moving, swallowing, mild hoarseness, urinary retention, and constipation. He also had a purple rash across his forehead.
MRI with contrast indicated edema of all muscle types visualized. Pathology of the patient’s purple rash confirmed a DM diagnosis. A bone marrow biopsy and immunohistochemistry staining with CD34, CD71, Factor VIII, and MPO was performed, revealing normocellular marrow with megakaryocyte hyperplasia, mild decrease in erythroid precursors, and moderate fibrosis, consistent with postpolycythemic MF. Staging was determined to be IPSS 2 (INT-1) and DIPSS 3 (INT- 2), high-intermediate to high-risk MF. Investigators concluded that the patient’s PV had converted to MF and the patient had DM associated with secondary MF.
“This case of postpolycythemic MF presents the possibility of an immune paraneoplastic mechanism associating secondary MF and DM. Regenerating muscle cells in myositis have been observed to express antigens similar to cancer tissue. In the setting of hematologic malignancy, a paraneoplastic immune response may inadvertently target muscle tissue leading to DM,” speculate the investigators.
The researchers suggest the potential of an alternative treatment targeting the JAK2 receptor with inhibitors, such as ruxolitinib or tofacitinib. Mutations that activate JAK2, such as the V617F mutation detected in this patient have been implicated in PV and MF. Furthermore, JAK kinase over activity has been linked to other autoimmune disorders. “Given its activity in both autoimmune and myeloproliferative processes, JAK2 inhibition would be a reasonable target in paraneoplastic DM,” conclude the investigators.