Persistent Dizziness in an Older Patient Due to Vitamin B12 Deficiency-Related Subacute Combined Degeneration (SCD) After Correction of Hyponatremia: A Case Report.

An 82-year-old woman presented with persistent dizziness that began one month earlier. Initial testing revealed severe hyponatremia (Na 104 mEq/L), and she was hospitalized for evaluation and fluid restriction, which normalized sodium levels. However, her dizziness persisted. The neurological examination revealed deep sensory impairment and lower motor neuron findings, without upper motor neuron signs. Laboratory testing revealed a markedly reduced vitamin B12 level (<148 pg/mL). Although spinal MRI showed no characteristic lesions of subacute combined degeneration (SCD), vitamin B12 deficiency was suspected as the underlying cause of her unsteadiness, and intravenous cyanocobalamin (1000 µg/day for 21 days) was administered. Her vibration sense improved, and she regained partial stability. This case highlights that vitamin B12 deficiency can manifest primarily as deep sensory disturbance without typical upper motor neuron signs or radiological findings, particularly in older adults. Excessive focus on concurrent metabolic abnormalities, such as hyponatremia, may delay recognition of neurological causes of dizziness. Clinicians should consider vitamin B12 deficiency or early SCD in elderly patients presenting with unexplained unsteadiness and perform thorough neurological assessments to enable timely treatment and prevent irreversible nerve damage.