452 - Pedal to the Metal: A Case of Isolated Foot Drop

Case Diagnosis: Pedal to the Metal: A Case of Isolated Foot Drop

Case Description: A 75-year-old male with a ten-year history of Waldenström macroglobulinemia (WM) and remote lumbar laminectomy was evaluated in an outpatient sports medicine clinic for four weeks of intermittent right foot numbness and weakness. His symptoms worsened while driving and extended from his right knee to his foot. On exam, the patient had full strength in his left lower extremity (LE) and right proximal LE, but had 0/5 strength in ankle dorsiflexion and plantarflexion and 1/5 strength in ankle inversion and eversion. His sensation to light touch was diminished in his bilateral LE distal to the knees. MRI of the lumbar spine showed moderate degenerative changes in L4-L5 with impingement of the L5 nerve root and L5-S1 disc bulge. However, needle EMG indicated severe polyneuropathy and acute-on-chronic right L5-S1 denervation, consistent with WM polyneuropathy instead of structural impingement. The patient's oncology team administered zanubrutinib for WM management.

Discussions: WM is a B-cell lymphoproliferative neoplasm with findings of small lymphocytes and monoclonal IgM gammopathy. WM can notoriously cause a variety of non-specific B symptoms. Additionally, WM is reportedly associated with non-focalized peripheral neuropathy as seen in this patient with an isolated foot drop. Treatment includes chemotherapy agents such as zanubrutinib, which our patient was started on. Interdisciplinary discussion across specialties including physiatry, oncology, and neurosurgery is imperative in treating polyneuropathy secondary to WM, especially with confounding lumbar imaging showing nerve root impingement. The discordant objective findings from the physical exam, EMG/NCS, and lumbar MRI highlights the difficulty in determining the true cause of an isolated foot drop in a seemingly healthy patient.
 

Conclusions: WM is a blood dyscrasia that can present with non-specific symptoms including foot drop. An interdisciplinary team is essential to confirm the etiology and determine subsequent treatment of this neurologic deficit.