Cogwheel Rigidity in Subacute Combined Degeneration Unresponsive to Vitamin B12 Therapy

Introduction Parkinsonian symptoms seen with B12 deficiency have been described in five cases where B12 therapy has led to their elimination. Subacute combined degeneration (SCD) presenting with parkinsonian signs of cogwheel rigidity, unresponsive to B12 supplementation, has not heretofore been described. Methods Case Study: This 62-year-old right-handed woman with a past medical history of hypothyroidism presented with complaints of trouble with memory. Cogwheel rigidity and pernicious anemia with low intrinsic factor and B12 levels (165 pg/ml) were found. SCD was diagnosed and treated with monthly B12 injections over the past three years, providing symptomatic relief, yet the cogwheeling persisted. She described never developing trouble with gait, movement disorders, autonomic abnormalities, olfactory dysfunction, disorders of sleep, visual hallucinations, or other parkinsonian symptoms. Results Abnormalities in Neurologic Examination: Cranial Nerve (CN) Examination: CN I: Alcohol Sniff Test: 9 (hyposmia). CN III, IV, VI: Bilateral ptosis. Motor Examination: 1+ Cogwheel rigidity both upper extremities. Drift Testing: Right pronator drift with left abductor digiti minimi sign. Reflexes: 3+ throughout other than 4+ ankle jerks. Quadriceps femoris bilaterally pendular. Bilateral Hoffman and Babinski reflexes present. B12 Level: 394 pg/ml (normal). Discussion While predominantly affecting the posterior columns and the lateral corticospinal tract, the demyelination may further extend into adjacent fibers including the reticulospinal tract and the rubrospinal tract, the tracts which, in Parkinson’s Disease, have been cited for their role in maintenance of tone and thus cogwheeling. Additionally, low B12 and elevated homocysteine levels have been noted as potential contributory factors in the pathogenesis of Parkinson’s Disease. It is also possible that this is a violation of Occam’s razor, that this individual has two separate distinct diseases — the prominent subacute combined degeneration as well as a subclinical parkinsonism which was revealed on neurologic examination. The parkinsonian signs may have been present prior to the B12 deficiency, and if not for the examination findings, could have remained undiscovered for decades. In those that present with Subacute Combined Degeneration, evaluation for parkinsonism is warranted. Funding No Funding