A 54-year-old woman is evaluated in the clinic due to easy fatigability. The patient has had no weight gain or cold intolerance, and has no history of thyroid problems. Her medical history is significant for gastrectomy due to a nonhealing gastric ulcer. Physical examination shows a shiny tongue and pale palmar creases. Her gait is unstable when her eyes are closed, and vibration sense is markedly decreased over the lower extremities. There is mild symmetrical loss of strength affecting the proximal lower extremity muscles. Blood hemoglobin level is 7.2 g/dL and white blood cell count is 3,600/mm³. Stool tests for occult blood are repeatedly negative. Which of the following spinal cord lesions is most likely present in this patient?

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11ec160b_35d4_c353_9249_31acc5e07e4e_MD0001_00 This patient is most likely suffering from subacute combined degeneration of the spinal cord, a condition that results from chronically low levels of vitamin B₁₂ (cobalamin). Low cobalamin levels may occur due to pernicious anemia (autoimmune gastritis with deficient intrinsic factor), gastrectomy, ileal resections, infection by the tapeworm Diphyllobothrium latum, and strict vegan diets containing no animal products for a prolonged period (4-5 years). Anemia along with neurologic abnormalities is typical of vitamin B₁₂ deficiency. Vitamin B₁₂ is an important cofactor in DNA synthesis; therefore, hematologic manifestations of vitamin B₁₂ deficiency include megaloblastic anemia and pancytopenia. Elevated levels of methylmalonic acid also result in myelin synthesis abnormalities. Neurologic damage associated with vitamin B₁₂ deficiency classically includes subacute combined degeneration of the dorsal columns (loss of position and vibration sensation, sensory ataxia [positive Romberg sign]), lateral corticospinal tracts (spastic paresis), and spinocerebellar tracts (contributes to ataxia). Patients may also develop atrophic glossitis, which appears as a smooth, shiny, erythematous tongue. (Choice A) Poliomyelitis and Werdnig-Hoffmann disease are associated with destruction of lower motor neurons in the anterior horn, which causes flaccid paralysis, muscle atrophy, and fasciculations. (Choice B) Multiple sclerosis is an inflammatory demyelinating disorder affecting the white matter of the central nervous system in a random and asymmetric pattern. Patients typically present with neurologic deficits disseminated in space and time. (Choice C) Tabes dorsalis (tertiary neurosyphilis) is characterized by degeneration of the dorsal root ganglia and dorsal columns. Although patients may have impaired vibratory sensation and proprioception, pancytopenia and atrophic glossitis are not characteristic. In addition, tabes dorsalis does not typically affect the lateral corticospinal tracts. (Choice E) Syringomyelia is a central cavitation of the cervical spinal cord that is associated with damage to the anterior white commissure of the spinothalamic tract. Patients typically have bilateral loss of pain/temperature in the upper extremities. Expansion into the ventral horns may result in flaccid paralysis of the hand muscles. Educational objective: Neurologic damage associated with vitamin B₁₂ deficiency classically includes subacute combined degeneration of the dorsal columns (loss of position and vibration sensation, positive Romberg sign) and lateral corticospinal tracts (spastic paresis). __________ References: Reversible myelopathy with vitamin B12 deficiency. (http://www.ncbi.nlm.nih.gov/pubmed/19037544)

A 54-Year-Old Woman Is Evaluated in the Clinic Due to Easy