A 60-year-old African-American woman sought evaluation after a syncopal episode. She complained of an unsteady gait for 3 weeks prior to hospital admission but denied dyspnea, chest pain, or dizziness. Her medical history was remarkable for well-controlled hypertension. There was no history of thrombosis, miscarriages, recent physical trauma, or prolonged air travel. The initial assessment revealed an ill-appearing woman with a BP of 110/75 mm Hg, heart rate of 130 beats/min, and respiratory rate of 25 breaths/min. Pulse oximetry was 94% on room air. A loud pulmonic component of the second heart sound and noncerebellar ataxia were present. The results of the rest of the physical examination were within normal limits. Laboratory data showed an increased mean corpuscular volume and a normal hemoglobin level. Biochemical and clotting profiles were normal. The ECG showed sinus tachycardia without right heart strain. Chest radiograph findings were normal. Arterial blood gas levels measured with the patients breathing room air revealed the following: pH, 7.46; Paco2, 25 mm Hg; and Po2, 73 mm Hg. Lower extremity Doppler scans were negative for deep venous thrombosis. The results of a ventilation/perfusion lung scan were abnormal (Fig 1
, middle, A). The patient received a diagnosis of pulmonary embolism and began therapy with IV heparin. Further extensive laboratory data are presented in Table 1
. She was discharged from the hospital while receiving therapy with homocysteine-lowering agents, including folate (1 mg/d), pyridoxine (100 mg/d), and high-dose oral cobalamin (1,500 μg/d). She continued to receive oral anticoagulation therapy for 6 months. Serum methylmalonic acid (MMA), homocysteine, and cobalamin levels normalized after 3 months of therapy (Table 1). A repeat ventilation/perfusion lung scan 6 months later demonstrated significant improvement (Fig 1, bottom, B). She recovered completely from her ataxia. After 1 year of follow-up, the results of the patient’s age-appropriate cancer screening examination has been negative. There have been no further episodes of thrombosis.