Anti-NXP2-antibody-positive immune-mediated necrotizing myopathy associated with acute myeloid leukemia: A case report.

RATIONALE: Idiopathic inflammatory myopathies have been extensively reported associated with malignancy. Immune-mediated necrotizing myopathy (IMNM), however, has rarely been connected with malignancy including acute myeloid leukemia (AML).

PATIENT CONCERNS: A 65-year-old woman was diagnosed with AML and received regular chemotherapy. After the 5th cycle chemotherapy, she achieved complete remission but developed severe muscle weakness and myalgia with dramatic increasing creatine kinase (CK).

DIAGNOSIS: The positivity of antinuclear matrix protein 2 antibody (anti-NXP2 Ab) and muscle biopsy in together confirmed the diagnosis of IMNM.

INTERVENTION: Methylprednisolone and intravenous immunoglobulin was administered.

OUTCOMES: This treatment resulted in a dramatic clinical and laboratory improvement within 1 month. CK and lactate dehydrogenase levels dropped sharply to normal. Anti-NXP2 Ab was shown to disappear in a repeated test afterwards.

LESSONS: The IMNM is also closely related to malignancy. We here report a case of IMNM associated with AML for the first time. Anti-NXP2 Ab may be utilized as both diagnostic and prognostic markers of paraneoplastic IMNMs.