307 - An Uncommon Cause of Weakness: Sacral Plasmacytoma and Paraproteinemic Neuropathy Identified During Pancreatic Mass Investigation and Incongruent Exam

Case Diagnosis: Sacral Plasmacytoma and Paraproteinemic Neuropathy

Case Description: A 49-year-old man presented with bilateral lower extremity weakness, distal numbness, and unintended weight loss spanning several months. A CT scan revealed pancreatic, hepatic, and sclerotic osseous lesions. Subsequent MRI exposed a sacral mass with additional osseous disease. The prevailing assumption for the etiology of his symptoms was metastatic pancreatic cancer with spine involvement. However, a physical examination by the PM&R consult team disclosed symmetric weakness in dorsiflexion and plantarflexion, and a length-dependent reduction in sensation, which was inconsistent with previous imaging. Given this incongruence, further investigations were proposed. Ultimately, the pancreatic mass was deemed non-malignant, while the sacral biopsy and hematologic studies were consistent with plasmacytoma and multiple myeloma. The diagnostic puzzle was further clarified by EMG and lumbar puncture, supporting the presence of paraproteinemic neuropathy. The patient was treated with radiation and chemotherapy. Symptoms persisted, but did not progress, and he was discharged to an inpatient rehabilitation facility.

Discussions: This case highlights the significance of conducting an in-depth workup following the onset of insidious weakness. It emphasizes the importance of correlating physical examination to findings on imaging and supports the concept that clinicians should consider potential alternative etiologies when discrepancies arise. This unique presentation of a paraproteinemic neuropathy was ultimately discovered more promptly due to the red herring of a benign pancreatic lesion and the mismatch between physical examination and imaging results.

Conclusions: The journey from insidious weakness to the unveiling of sacral plasmacytoma and paraproteinemic neuropathy underscores the necessity of a meticulous approach to patient evaluations and brings to light the intricate nature of clinical diagnosis.