Case Presentation: A 23-year-old female with a one-year history of intermittent back pain who presented to an outside hospital with acutely worsened low back pain, and new onset left leg weakness, constipation, and urinary retention. She did not have health insurance and was unable to seek proper medical care. She had been told her pain was possibly from inflammation of her sciatic nerve. MRI of the lumbar spine done at the outside hospital demonstrated an expansile sacral mass. She was then transferred to a tertiary care center for additional work-up and treatment. Upon arrival, she reported severe lower back pain, constipation, and urinary retention. Physical exam revealed saddle anesthesia and numbness/weakness of the left lower extremity. She was placed on a hydromorphone patient-controlled analgesia pump. Pain control remained difficult during her admission, necessitating involvement of the pain management team. Other pain medications included tizanidine, oxycodone, ketorolac, acetaminophen, gabapentin, baclofen, methocarbamol, lidocaine patches, and diclofenac gel. Neurosurgery was consulted and recommended CT-guided biopsy of the sacral mass and conservative management. CT scan redemonstrated the sacral mass compressing the spinal canal and neural foramina. MRI brain, T-spine, and C-spine were negative for metastatic disease. Lab work was significant for pseudohyponatremia in the setting of hyperproteinemia with elevated free kappa, kappa: lambda ratio, and serum IgG. CT-guided biopsy of the sacral mass demonstrated sacral plasmacytoma. Bone marrow biopsy demonstrated multiple myeloma. She was taken for emergent external-beam radiation treatment by radiation oncology and initiated on IV steroids by hematology/oncology. She went on to complete a 12-day inpatient radiation therapy course prior to discharge, with planned outpatient follow-up for systemic therapy (DARA-VRd) followed by autologous stem cell transplantation.
Discussion: The incidence of plasmacytoma in newly diagnosed multiple myeloma is relatively rare, with occurrence between 3.5-18%1. Additionally, multiple myeloma is very rare in young patients, with diagnosis before 40 years of age representing < 2% of all patients2. Symptoms of MM and plasmacytoma include bone pain, fatigue, weight loss, constipation, and nausea. High dose chemotherapy plus autologous stem-cell transplantation (ASCT) is still considered the standard of care.
Conclusions: Although extremely rare in this age demographic, this case demonstrates the importance of keeping multiple myeloma on the differential in young patients with severe bone pain and neurologic symptoms without clear etiology. Delay in a thorough workup can lead to complications such as pathological fractures, renal failure, and cauda equina syndrome. Indications for imaging in adults with low back pain include severe or progressive neurologic deficits and signs of cauda equina syndrome (urinary retention/incontinence, fecal incontinence, saddle anesthesia, significant motor deficits).
