Polymyalgia Rheumatica or Something Else? Bilateral Shoulder, Arm, and Thigh Pain with Diffuse Marrow Edema Revealing B-cell Acute Lymphoblastic Leukemia.

Background B-cell acute lymphoblastic leukemia (B-ALL) is an uncommon malignancy in adults. Polymyalgia rheumatica-like syndromes are rare and present features that can lead to a diagnostic delay. Magnetic resonance imaging (MRI) may reveal diffuse bone-marrow abnormalities. However, these findings are often nonspecific. Case Presentation A Japanese woman in her 40s presented with persistent pain in the bilateral shoulders, upper arms, and thighs. Initial laboratory tests showed anemia and elevated C-reactive protein levels, but no blasts were detected in the peripheral blood. Polymyalgia rheumatica was suspected; however, her age, absence of morning stiffness, and symmetrical diaphyseal pain were atypical for this condition. MRI revealed diffuse T2-short tau inversion recovery hyperintensity and patchy enhancement in the femoral and humeral shafts and adjacent muscles, without the dominant bursitis or synovitis typical of polymyalgia rheumatica. Bone marrow biopsy revealed hypercellularity with numerous CD19-positive lymphoblasts, leading to a diagnosis of B-ALL. Induction chemotherapy resulted in rapid pain relief and normalization of the clinical findings. Conclusion This case highlights that hematologic malignancies, including B-ALL, can present with polymyalgia rheumatica-like symptoms in adults. MRI is useful for detecting bone marrow infiltration and should prompt early bone marrow examination. Recognizing atypical features in presumed polymyalgia rheumatica and avoiding premature glucocorticoid therapy may prevent delays in the diagnosis of life-threatening conditions such as leukemia.