BACKGROUND: Propylthiouracil (PTU) therapy is associated with a variety of 
adverse reactions, among the most rare being interstitial pneumonia. To date, 
this has been reported in four Asian patients with autoimmune hyperthyroidism. 
Here we describe a Caucasian woman who developed a bronchiolitis obliterans 
organizing pneumonia (BOOP)-like interstitial pneumonia after PTU administration 
for amiodarone-induced thyrotoxicosis.
PATIENT FINDINGS: The patient was a 68-year-old woman who had been treated with 
amiodarone for chronic atrial fibrillation starting in May 2004. She had been a 
heavy smoker with a history of hypertension but no dust exposures. In October 
2006, amiodarone was stopped after she developed thyrotoxicosis. In January 2007 
serum thyroid-stimulating hormone (TSH) was 0.01 mIU/L (0.35-4.94) and free T4 
was 17.5 pg/mL (7 to 15). She was initially started on methimazole and then 
changed to PTU after she developed pruritus. She developed severe dyspnea 9 
months after starting PTU. At the time she was also taking warfarin, enalapril, 
and sotalol. Chest X-ray showed diffuse interstitial peripheral opacities and 
transbronchial lung biopsy revealed subacute lung injury with organizing 
pneumonia with hyperplasia of the alveolar type 2 pneumocytes, and 
characteristics of BOOP-like interstitial pneumonia. Signs and symptoms 
progressively improved after PTU discontinuation as confirmed at X-ray and 
computed tomography (CT) scan of the chest and by respiratory function tests. 
She has been recurrence free for 4 years after stopping PTU.
SUMMARY: This woman of Caucasian ancestral origin developed BOOP-like 
interstitial pneumonia after PTU treatment for apparent amiodarone-induced 
thyrotoxicosis, with resolution of her lung disease after stopping PTU. Tests 
for TSH receptor antibodies, thyroid peroxidase antibodies, and antinuclear 
cytoplasmic autoantibody were negative. Thyroid ultrasound was consistent with 
thyroiditis without nodules.
CONCLUSIONS: PTU-associated interstitial pneumonia is not limited to patients of 
Asian origin or those with autoimmune thyroid disease. PTU must be withdrawn in 
the presence of respiratory symptoms and documented interstitial pneumonia. 
X-ray films, CT-scan, respiratory function tests, and lung biopsy are needed to 
diagnose PTU-induced interstitial pneumonia with certainty and to monitor the 
evolution of the disease after PTU discontinuation.