A 57-year-old man comes to the office due to several months of persistent tingling in both legs. The patient also says he feels clumsy and often bumps into furniture. He has a history of hip osteoarthritis, but the pain is well controlled with acetaminophen and occasional ibuprofen and does not limit his mobility. The patient also has a history of gastroesophageal reflux disease and Barrett esophagus; he has used omeprazole for the past several years and has had no recent heartburn or dysphagia. He does not use tobacco, alcohol, or illicit drugs. The patient consumes a balanced diet and walks 1 or 2 miles every other day. Vital signs are within normal limits. Lower extremity muscle strength is intact. Sensation to light touch and vibration are diminished in the feet bilaterally. The remainder of the physical examination shows no abnormalities. Which of the following is the most appropriate next step in evaluation of this patient's symptoms?

Question

A 57-year-old man comes to the office due to several months of persistent tingling in both legs.  The patient also says he feels clumsy and often bumps into furniture.  He has a history of hip osteoarthritis, but the pain is well controlled with acetaminophen and occasional ibuprofen and does not limit his mobility.  The patient also has a history of gastroesophageal reflux disease and Barrett esophagus; he has used omeprazole for the past several years and has had no recent heartburn or dysphagia.  He does not use tobacco, alcohol, or illicit drugs.  The patient consumes a balanced diet and walks 1 or 2 miles every other day.  Vital signs are within normal limits.  Lower extremity muscle strength is intact.  Sensation to light touch and vibration are diminished in the feet bilaterally.  The remainder of the physical examination shows no abnormalities.  Which of the following is the most appropriate next step in evaluation of this patient's symptoms?

Quizplus · Accepted Answer

11ec25c8_d0da_0ab5_bc81_494b47bcde22_MD0003_00 This patient's omeprazole use, lower extremity paresthesia, and diminished light touch/vibration sensation in the feet raise strong suspicion for vitamin B₁₂ deficiency. Because vitamin B₁₂ is an essential cofactor for DNA synthesis and myelin formation, deficiency usually manifests with hematologic (eg, megaloblastic anemia) and/or neurologic abnormalities. Common neurologic findings include subacute combined degeneration of the dorsal columns (eg, impaired proprioception/vibrioception) and the lateral corticospinal tracts (eg, positive Babinski reflex), but patients often first develop symmetric lower extremity paresthesia due to myelinated peripheral nerve damage. Vitamin B₁₂ is ingested bound to animal protein and must be liberated in the stomach by pepsin, which is activated from pepsinogen by gastric acid. Therefore, patients on long-term proton pump inhibitor therapy (eg, omeprazole) sometimes develop vitamin B₁₂ deficiency due to achlorhydria. Older patients are particularly at risk. The diagnosis is usually made with serum vitamin B₁₂ level, but methylmalonic acid or homocysteine testing may be necessary if this test is inconclusive. (Choice A) HIV can cause a distal symmetric polyneuropathy that generally begins with tingling and numbness in the bilateral feet. However, all sensory modalities are typically diminished (not just light touch and vibration), reflexes are generally impaired, and neuropathic pain is usually prominent. (Choice B) Neurologic manifestations (eg, peripheral neuropathy, paresthesias) can develop in multiple myeloma (MM), which is diagnosed by serum protein electrophoresis. However, they are typically due to plasmacytoma infiltration or paraneoplastic effects and are not usually present at initial diagnosis. MM is unlikely in this patient with no other suggestive features (eg, bone pain, anemia). Most patients with neurologic manifestations of MM have significant neuropathic pain and mixed sensory and motor abnormalities. (Choice D) Urine heavy metal testing can diagnose lead poisoning, which is often associated with peripheral neuropathy. However, peripheral motor neurons are primarily affected; therefore, most patients have motor weakness (eg, wrist or ankle drop). (Choice E) Chronic hepatitis C virus infection can cause mixed cryoglobulinemia, which is associated with peripheral neuropathy. However, most cases are marked by both sensory and motor abnormalities; and patients often have palpable purpura and arthritis or arthralgias. This patient's acid suppression and signs of dorsal spinal cord injury make vitamin B₁₂ deficiency more likely. Educational objective: Older patients with a history of chronic antacid use are at risk for vitamin B₁₂ deficiency due to achlorhydria. These patients frequently have subtle neurologic findings, including lower extremity paresthesias and signs of dorsal column injury (eg, diminished light touch/vibration sensation). A serum vitamin B₁₂ test is usually diagnostic, but methylmalonic acid or homocysteine testing may be required for confirmation in inconclusive cases.

A 57-Year-Old Man Comes to the Office Due to Several