A 58-year-old woman presents to her primary care physician with complaints of several weeks of progressively worse fatigue, bilateral lower extremity paresthesias, and feelings of unsteadiness while ambulating. Past medical history is significant for gastroesophageal reflux disease, for which she takes pantoprazole. She became vegetarian about five years ago. The patient denies headache, fever, chills, bowel or bladder incontinence, or nausea. She reports additional symptoms of occasional loss of appetite and lightheadedness. Vital signs are temperature 36°C (98.6°F), blood pressure 110/78 mmHg, pulse 61 beats/min, and respirations 19/min. Body mass index (BMI) is 25 kg/m2. Physical examination reveals diminished sensation in the bilateral lower extremities, muscle stiffness, loss of bilateral ankle reflexes, and a positive Romberg sign. Additionally, conjunctival pallor is noted. Lab values are as follows:
C) Subacute combined degeneration
This condition usually presents secondary to vitamin B12 deficiency, which is consistent with this patient’s history. She has been taking a proton-pump inhibitor (which can cause pernicious anemia), is practicing vegetarianism, has a macrocytic anemia (an MCV greater than 115 um3 is usually more specific for B12 deficiency), and has neurological symptoms suggestive of this condition. Subacute combined degeneration affects the spinocerebellar tract, lateral corticospinal tract, and dorsal columns. This patient’s symptoms and physical exam findings correlate with these tracts being affected.
Answer choice A: Friedrich ataxia, is incorrect. This condition is usually seen in younger patients and does not present with corticospinal tract symptoms such as loss of ankle reflexes.
Answer choice B: Iron deficiency anemia, is incorrect. Iron deficiency anemia can present with fatigue and conjunctival pallor, but on laboratory work-up would show microcytic anemia, not macrocytic anemia.
Answer choice D: Transverse myelitis, is incorrect. This condition does not usually involve the dorsal columns, so paresthesias would not be observed. Additionally, bowel and bladder symptoms would be observed.
Answer choice E: Vacuolar myelopathy, is incorrect. This condition is usually seen in the context of HIV-positive individuals with low CD4+ counts. It presents similarly to subacute combined degeneration, but the patient’s history would include recent opportunistic infections and a history of HIV infection.
Key Learning Point
Subacute combined degeneration is caused by B12 deficiency, which can present secondary to pernicious anemia or following a vegetarian diet. It presents with symptoms related to damage to the spinocerebellar, lateral corticospinal, and dorsal column tracts.
