A 45-year-old man comes to the office due to 3 months of night sweats, productive cough, decreased appetite, and a 5-kg (10-lb) weight loss. He travels frequently to Vietnam. Vital signs are normal. Examination reveals crackles in the right upper lobe of the lung. Chest x-ray reveals a right upper lobe infiltrate. Acid-fast bacilli are present on sputum smear. The patient is started on combination therapy with isoniazid, ethambutol, rifampin, pyrazinamide, and pyridoxine. One month later, he returns to the office reporting blurring of vision. Examination shows bilateral central scotomas. Which of the following is most likely responsible for this patient's visual symptoms?

Question

A 45-year-old man comes to the office due to 3 months of night sweats, productive cough, decreased appetite, and a 5-kg (10-lb) weight loss.  He travels frequently to Vietnam.  Vital signs are normal.  Examination reveals crackles in the right upper lobe of the lung.  Chest x-ray reveals a right upper lobe infiltrate.  Acid-fast bacilli are present on sputum smear.  The patient is started on combination therapy with isoniazid, ethambutol, rifampin, pyrazinamide, and pyridoxine.  One month later, he returns to the office reporting blurring of vision.  Examination shows bilateral central scotomas.  Which of the following is most likely responsible for this patient's visual symptoms?

Quizplus · Accepted Answer

11ec160b_3bfe_ac56_9249_53c7a7515fd0_MD0001_00 This patient, who travels regularly to Vietnam and now has a cough, night sweats, and weight loss with a right upper lobe infiltrate on chest x-ray and acid-fast bacilli on sputum examination, likely has pulmonary tuberculosis (TB). Pulmonary TB is treated with a 4-drug regimen, sometimes referred to as RIPE: rifampin, isoniazid (INH), pyrazinamide, and ethambutol. The most notable side effect of ethambutol is optic neuropathy, which clinically manifests as decreased visual acuity, central scotoma, or color blindness. It may be reversible with discontinuation of the drug. (Choices B and D) The most important side effect of INH is hepatotoxicity. INH is also associated with peripheral neuropathy, which is due to the drug's interference with pyridoxine metabolism and can be prevented by pyridoxine administration. (Choice C) The most important side effects of pyrazinamide are hepatotoxicity and hyperuricemia (can exacerbate gout). (Choice E) Rifampin can cause body fluids (eg, urine, tears) to turn red. This condition is benign. Educational objective: Ethambutol can cause optic neuropathy that results in color blindness, central scotoma, and decreased visual acuity. This adverse side effect may be reversed with discontinuation of the drug.

A 45-Year-Old Man Comes to the Office Due to 3