CASE PRESENTATION: A 62 year old female with a past medical history of breast cancer status post resection, severe COPD and stable pulmonary nodules was followed in our practice for evaluation of lung volume reduction surgery secondary to persistent respiratory symptoms. Surveillance CT scan showed a 2 mm apical cavitary lesion with scarring for which she underwent a bronchoscopy. Her cultures were positive for mycobacterium avium complex (MAC). She was started on a triple drug regimen including isoniazid, ethambutol 400 mg twice daily, and azithromycin with good clinical response. Her sputum cultures were negative 2 months after initiation of the treatment; however, at subsequent follow-up appointments she started complaining of bilateral lower extremity sensory deficits. An EMG was performed with results consistent with a sensory polyneuropathy. Routine ophthalmological examination also revealed peripheral vision deficit more pronounced in the right eye. Both of these side effects were attributed to ethambutol which was discontinued with improvement of her symptoms.