Multiple Myeloma Presenting as Cauda Equina Syndrome: A Rare and Early Spinal Manifestation.

Introduction: Multiple myeloma (MM) is a malignant plasma cell disorder commonly affecting the axial skeleton, with vertebral compression fractures frequently observed. However, isolated lumbosacral vertebral collapse leading to acute cauda equina syndrome (CES) as the first clinical manifestation is extremely rare. This case highlights the importance of suspecting underlying malignancy in elderly patients presenting with acute spinal cord compression without trauma or systemic symptoms. Case Report: A woman in her late 60s presented with acute lower limb weakness, urinary incontinence, and constipation. Examination revealed sensory deficits below L5, reduced motor strength in foot muscles, and an absent bulbocavernosus reflex, consistent with CES. Imaging showed L5 vertebral collapse with canal compromise. Magnetic resonance imaging suggested a pathological fracture, and positron emission tomography-computed tomography confirmed a solitary lesion. Serum protein electrophoresis showed M-protein, and histopathology confirmed MM. The patient underwent posterior decompression and instrumentation followed by bisphosphonate therapy and local radiation. At 1-year follow-up, she regained full neurological function and resumed normal activities. Conclusion: Isolated vertebral involvement in MM may rarely present as CES and should be considered in elderly patients with acute spinal syndromes, even in the absence of systemic signs. Prompt diagnosis, surgical decompression, and targeted therapy can lead to excellent recovery. This case underscores the value of multidisciplinary care and raises awareness of atypical spinal presentations of MM.