A 65-year-old woman comes to the physician because of unsteadiness and near-falls over the last 6 months. In the evening, she has to hold on to the wall in the hallway while going to the bathroom. She also complains of bilateral knee pains, occasional low back pain, and difficulty falling asleep. She is concerned that she has become more forgetful than usual. She denies dizziness, headaches, blurry vision, or weight loss. She has hypothyroidism, osteoporosis, and hypertension. Current medications include risedronate, hydrochlorothiazide, vitamin D, and levothyroxine. Her mother suffered from dementia and died at the age of 75. Her mammogram results 1 year ago and colonoscopy results 3 years ago were unremarkable.
Her blood pressure is 133/82 mmHg while supine and 135/85 mmHg while standing, and pulse is 78/min. On neurologic exam, position and vibration sensation is diminished in both feet as well as a slight decrease in light touch sensation. Cranial nerves are intact. Motor strength is normal and symmetric. Deep tendon reflexes are symmetric and decreased in her feet. There are no pathologic reflexes. Her score on a Folstein mini-mental status exam is 26/30.
The patients labs reveal:

Which of the following is the most appropriate next step in management?

Question

A 65-year-old woman comes to the physician because of unsteadiness and near-falls over the last 6 months.  In the evening, she has to hold on to the wall in the hallway while going to the bathroom.  She also complains of bilateral knee pains, occasional low back pain, and difficulty falling asleep.  She is concerned that she has become more forgetful than usual.  She denies dizziness, headaches, blurry vision, or weight loss.  She has hypothyroidism, osteoporosis, and hypertension.  Current medications include risedronate, hydrochlorothiazide, vitamin D, and levothyroxine.  Her mother suffered from dementia and died at the age of 75.  Her mammogram results 1 year ago and colonoscopy results 3 years ago were unremarkable.
Her blood pressure is 133/82 mmHg while supine and 135/85 mmHg while standing, and pulse is 78/min.  On neurologic exam, position and vibration sensation is diminished in both feet as well as a slight decrease in light touch sensation.  Cranial nerves are intact.  Motor strength is normal and symmetric.  Deep tendon reflexes are symmetric and decreased in her feet.  There are no pathologic reflexes.  Her score on a Folstein mini-mental status exam is 26/30.
The patients labs reveal:

Which of the following is the most appropriate next step in management?

Quizplus · Accepted Answer

Cobalamin deficiency has been found in 12% of free-living elderly Americans. In many of these individuals, the classic hematologic manifestations of cobalamin deficiency such as anemia, macrocytosis, leukopenia, thrombocytopenia, hypersegmented polymorphonuclear leukocytes, and an elevated LDH are not present. Moreover, some of these individuals have serum concentrations of cobalamin in the low normal range (200 to 300 pg/mL). These individuals often have hard to describe neuropsychiatric symptoms such as paresthesias, numbness, weakness, loss of dexterity, decreased memory, and personality changes that improve with cobalamin replacement. Cobalamin is a cofactor in the metabolism of methylmalonic acid, and B12 deficiency leads to decreased metabolism of methylmalonic acid and increased serum levels. Determination of a serum methylmalonic acid level is diagnostically helpful if the clinical situation suggests cobalamin deficiency in the presence of a cobalamin level within the normal range. The combination of this patient's complaints, physical exam findings compatible with posterior spinal column pathology, and the low normal serum cobalamin level strongly suggest cobalamin deficiency. (Choice A) ANA, ESR, and C-reactive protein are useful in diagnosing certain autoimmune diseases. This patient's joint pain and back pain are more likely related to osteoarthritis than an autoimmune condition. Also, she has no rashes or muscle weakness to suggest an inflammatory condition associated with abnormalities in these three laboratory markers. (Choice B) This patient has no systemic symptoms (e.g., fever, chills, weight loss) to suggest a malignancy and also had a recent normal mammogram and colonoscopy. Her neurological symptoms are more consistent with likely cobalamin deficiency rather than a malignancy. (Choice C) The presence of cognitive abnormalities prompts consideration of a central nervous system abnormality. However, this patient has a normal mini mental status exam and findings that are more consistent with cobalamin deficiency that should be confirmed first before proceeding with brain imaging, especially given the lack of other focal neurological findings. (Choice E) Some patients with a paraproteinemia may present with peripheral neuropathy, but this patient's other findings are more compatible with cobalamin deficiency. Educational objective: Symptomatic cobalamin deficiency can be present in the absence of macrocytic anemia and a reduction of serum cobalamin below the lower limit of normal. In this setting, an elevated serum methylmalonic acid is an important adjunctive test to confirm a diagnosis of cobalamin deficiency. __________ References: Prevalence of cobalamin deficiency in the Framingham elderly population (http://www.ncbi.nlm.nih.gov/pubmed/8017332) Clinical spectrum and diagnosis of cobalamin deficiency (http://www.ncbi.nlm.nih.gov/pubmed/2393714)

A 65-Year-Old Woman Comes to the Physician Because of Unsteadiness