Neutrophilic Myositis without Cutaneous Involvement as the First Manifestation of Acute Myeloid Leukemia
A previously healthy 35-year-old male complained of intermittent fever and myalgia of 1-month duration. On admission, he was febrile (39.2℃), with painful tenderness of the edematous upper arm; however, the overlying skin had no grossly abnormality. Ultrasonography showed a diffusely increased echogenicity in his thickened triceps, brachialis and gluteus muscles. Therefore, a magnetic resonance imaging study was performed ().\nA confirmatory muscle biopsy was performed on his left triceps and brachialis muscles. These histological specimens showed severe myositis, with predominantly dense infiltration of mature neutrophils, associated disruption of the muscle architecture and tissue necrosis (). Microbiological studies and serology for auto-antibodies were negative.\nThe initial complete blood count revealed an elevated white blood cell count of 20,440/mm3, with a differential count of 7% segmented neutrophils, 22% lymphocytes and 40% blast cells, which were strongly suggestive of leukemia. The serum chemistry studies disclosed an elevated lactate dehydrogenase level of 977 U/L. The patient subsequently underwent a diagnostic bone marrow aspiration and biopsy, which showed replacement of the normal bone marrow with myeloblasts. The flow cytometric findings were positive for CD13, but negative for CD33, CD14 and HLA-DR. Cytogenetic studies showed a normal karyotype (46,XY[20]). PCR of AML1/ETO was negative. On the basis of the flow cytometry and cytogenetic studies, the final diagnosis was confirmed as a M2 subtype of acute myeloid leukemia, with paraneoplastic neutrophilic myositis. Concomitant treatment with corticosteroid and induction chemotherapy was started. The fever, myalgia and swelling of both the upper arms were resolved after 5 days of steroid therapy.\nAn ultrasonography after 6 weeks of therapy demonstrated resolution of the muscle swelling seen at diagnosis. After the induction chemotherapy, and 2 courses of consolidation, followed by autologous stem cell transplantation, hematological remission was maintained for 15 months. The lack of stem cell sources limited the salvage therapy for the first relapse due to chemotherapy. At present, the patient is on close follow-up in the third hematological relapse. After the initial diagnosis, neither myalgia nor fever reappeared for 36 months.