A 35-year-old woman comes to the office due to 4 weeks of worsening fatigue and painful paresthesia in her feet. She has no back pain, gait disturbance, muscle weakness, or bowel or bladder symptoms. The patient has a history of Crohn disease that required an intestinal surgery. She does not use tobacco, alcohol, or illicit drugs. Temperature is 36.9 C (98.4 F), blood pressure is 110/70 mm Hg, pulse is 80/min, and respirations are 16/min. Muscle strength is 5/5, deep tendon reflexes are intact, and vibration and proprioception are preserved. Gait is normal. Laboratory results are as follows: Which of the following is the most appropriate next step in management of this patient?

Question

A 35-year-old woman comes to the office due to 4 weeks of worsening fatigue and painful paresthesia in her feet.  She has no back pain, gait disturbance, muscle weakness, or bowel or bladder symptoms.  The patient has a history of Crohn disease that required an intestinal surgery.  She does not use tobacco, alcohol, or illicit drugs.  Temperature is 36.9 C (98.4 F), blood pressure is 110/70 mm Hg, pulse is 80/min, and respirations are 16/min.  Muscle strength is 5/5, deep tendon reflexes are intact, and vibration and proprioception are preserved.  Gait is normal.  Laboratory results are as follows:  Which of the following is the most appropriate next step in management of this patient?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d568_ba74_bc81_15a13b8519a4_MD0003_00 This patient's anemia, borderline-elevated mean corpuscular volume (MCV), and bilateral foot paresthesia raises suspicion for vitamin B₁₂ deficiency. Patients with inflammatory disorders of the small bowel (eg, Crohn disease) are at increased risk due to reduced absorption of the intrinsic factor-vitamin B₁₂ complex in the ileum. ₁₂ ₁₂ Vitamin B₁₂ is essential for DNA synthesis (via reduction of 5-methyltetrahydrofolate to tetrahydrofolate) and myelin formation (via methylation of neuronal lipids and proteins); deficiency most often impacts: ₁₂ Rapidly dividing hematologic cells - increased apoptosis causes anemia and mild thrombocytopenia/leukopenia. Slowing of nuclear maturation usually results in macrocytosis (elevated MCV), but those with concomitant iron deficiency from gastrointestinal blood loss (as often occurs in Crohn disease) may have minimal or no MCV elevation. Myelinated nerve fibers - patients classically develop subacute combined degeneration, which is marked by demyelination of the dorsal column of the spinal cord (eg, reduced vibratory sensation, sensory gait ataxia) and the lateral corticospinal tracts (eg, spastic paresis, enhanced reflexes). However, myelinated nerves in the peripheral nervous system are often affected first, leading to lower extremity paresthesias with no other neurologic findings. Initial workup begins with serum B₁₂ testing; methylmalonic acid and homocysteine levels should be ordered for those with borderline/inconclusive results. ₁₂ (Choice A) HIV-associated peripheral neuropathy often causes bilateral tingling/numbness in the toes, but all sensory modalities (eg, touch, temperature, vibration, proprioception) will be impaired on examination. (Choice B) Lumbar puncture can help diagnose Guillain-Barré syndrome, an immune-mediated polyneuropathy most common after Campylobacter infection. Although bilateral paresthesia is common, almost all patients have concurrent, symmetric, lower extremity muscle weakness and areflexia. (Choice C) Spine MRI could diagnose transverse myelitis, which is usually marked by rapidly progressive flaccid paralysis, a sensory level, and bowel/bladder dysfunction. (Choice D) Serum protein electrophoresis can diagnose monoclonal gammopathy (eg, multiple myeloma). Although monoclonal gammopathy can cause light chain-related amyloidosis, which sometimes presents with polyneuropathy and normocytic anemia, this is very rare in individuals age <40. (Choice F) Mercury toxicity can be detected by 24-hour urine testing. It can cause distal paresthesia, but most patients have motor neuropathy with weakness and areflexia. Educational objective: Vitamin B₁₂ deficiency is common in those with chronic malabsorption (eg, Crohn disease) and often presents with macrocytic anemia and neurologic findings (eg, paresthesia, subacute combined degeneration). A vitamin B₁₂ level is the initial test of choice, but serum methylmalonic acid and homocysteine testing should be ordered in borderline or inconclusive cases. ₁₂ ₁₂ References: Update on vitamin B12 deficiency. (http://www.ncbi.nlm.nih.gov/pubmed/21671542)

A 35-Year-Old Woman Comes to the Office Due to 4