Acute promyelocytic leukemia with concurrent myeloid sarcoma is a rare clinical event. Herein we describe a patient that presented with back pain and bilateral leg weakness caused by spinal cord compression due to extramedullary deposition of leukemic cells. Acute promyelocytic leukemia was suspected based on immunophenotypic findings of malignant cells in bone marrow aspirate. The diagnosis was confirmed by the presence of PML-RARα fusion copies. MRI showed multiple hyperintense changes on the vertebral bodies, together with intraspinal masses causing spinal cord compression. The patient immediately underwent radiotherapy, and was treated with all-trans retinoic acid and idarubicin. Reassessment MRI showed complete resolution of all intraspinal masses and the disappearance of most of the bony lesions. Post-treatment bone marrow aspirate showed complete hematological and molecular remission. The motor power of his legs fully recovered from 0/5 to 5/5; however, sensory loss below the T4 level persisted.

Background: Measurement of serum free light chains (FLCs) has recently become available for the diagnosis and monitoring of patients with plasma cell dyscrasias. The aim of this study was to investigate the performance of the serum FLC assay as a tumour marker by comparing FLC concentrations with serum protein electrophoresis (PE) results in the diagnosis of multiple myeloma (MM). In addition, we also evaluated the prognostic value of the baseline serum FLC ratio in patients with MM. Methods: We measured FLC concentrations and calculated the kappa/lambda (k/l) FLC ratios for three groups (control, polyclonal gammopathy and MM). Results:The FLC ratio at a cut-off threshold of 2.0 showed higher sensitivity and specificity compared with serum electrophoresis for the diagnosis of MM. We used the median FLC ratio of )57.5 and -0.04 for k and l secretors, respectively, for assessing survival. Survival was 30 months in patients with the k/l ratio of )57.5 and -0.04 compared to 47 months in patients with the ratio -57.5 and )0.04, indicating that more abnormal serum FLC ratios are associated with poorer survival (p-0.011). Conclusions: Despite the limitations of the assay, the results of our study indicate that the FLC assay in combination with serum PE has an increased sensitivity in the diagnosis of MM. Also, baseline measurement of the k/l ratio provides prognostic information in these same patients.