Pathologic Quiz Case: Cauda Equina Syndrome in a 65-Year-Old Man, Status Post–Bone Marrow Transplant for Chronic Myeloid Leukemia

65-year-old man with a history of chronic myeloid leukemia (CML) presented with fatigue, a 9-kg weight loss, and increasing low back and buttock pain. He had received an allogeneic stem cell transplant 11 months previously. His medications on admission included cyclosporine and prednisone. On arrival, he noted difficulty initiating urination and complained of the inability to completely void. Presenting vital signs were normal except for temperature up to 39.48C. Back and extremity examination revealed exquisite tenderness over the lumbosacral spine and associated leg pain with straight leg testing. Motor examination revealed 4/5 normal strength of the hip flexors. Sensation to light touch and vibration was absent below the ankles bilaterally, and reflexes were diminished or absent at the knees and ankles. Laboratory data revealed a white blood cell count of 9700/mL, hematocrit of 0.29, and platelet count of 126 000/mL. The patient’s lactate dehydrogenase level