A 19-year-old man was referred for further management given a history of recurrent pneumothoraces and a recent CT of the thorax which revealed multiple bilateral pulmonary cysts.
His past medical history included a surgically resected osteochondroma from the medial aspect of his right tibia a year ago, a remote appendectomy, and a childhood diagnosis of asthma. He did not take any medications regularly. He smoked half a pack of cigarettes a day for the last six years and also smoked seven marijuana joints per day. He denied consuming alcohol or any other illicit drugs. He worked in the family restaurant and both of his parents smoked tobacco. Other than chest pain and dyspnea experienced at the time he was diagnosed with pneumothoraces, he denied any symptoms. He did describe drinking about 15 liters of water a day due to a dry mouth. He denied any bone pain, skin rashes, or abdominal pain. Review of systems was unremarkable.
Prior to referral, he had presented to hospital with a spontaneous right-sided pneumothorax on two occasions and bilateral pneumothoraces on one occasion. The third time he was treated surgically and a video-assisted thoracoscopic bullectomy with apical pleurectomy of the right lung was performed. He was found to have asymptomatic recurrence of a right-sided pneumothorax when seen in follow-up and was treated successfully with chemical pleurodesis in the form of bleomycin.
On examination, he was afebrile, blood pressure was 115/75, heart rate was 88 beats/min, and respiratory rate was 16 breaths/min. Weight was 93.5 kg and height 183 cm, resulting in a BMI of 27.9. The cardiovascular examination was normal except for a loud P2. The respiratory examination revealed normal breaths sounds bilaterally. The remainder of the examination was unremarkable.
Pulmonary function tests revealed airflow obstruction with an FEV1/FVC ratio of 43% (normal >= 70%), an FEV1 of 2.14 L (44% of predicted), and a FVC of 4.95 L (86% of predicted). There was no evidence of restriction and the diffusion capacity for carbon monoxide (DLCO) was decreased at 60%. His spirometry did demonstrate significant reversibility postbronchodilator. A CT of the thorax performed prior to referral showed bilateral thin-walled pulmonary cysts of variable sizes and irregular shapes (see the following list). There were a few ill-defined centrilobular nodules and no consolidation, pleural effusions, or lymph node enlargement (Figures 1(a), 1(b), and 1(c)).
Langerhans cell histiocytosis
Lymphoid interstitial pneumonia
Neurofibromatosis
Birt-Hogg-Dube syndrome
Pneumatoceles (due to prior Pneumocystis carinii pneumonia)
Tuberous sclerosis
Lymphangioleiomyomatosis
The following are the differential diagnoses of cystic lung disease: 
The patient's clinical presentation and investigations were consistent with the diagnosis of pulmonary Langerhans cell histiocytosis (PLCH) and possibly concurrent asthma. In fact, a previous bullectomy specimen showed histological features consistent with PLCH (Figures 2(a) and 2(b)). Given his history of polydipsia, he underwent a brain MRI which showed focal nodular thickening with enhancement of the infundibulum with otherwise normal size of the pituitary gland; findings were found to be consistent with posterior pituitary involvement (Figures 3(a) and 3(b)). Subsequent bloodwork showed a high-normal plasma sodium concentration of 142 mmol/L and a urine osmolality of 91 mmol/k, less than the plasma osmolality of 294 mmol/k. He did not have evidence of any other endocrinopathy on bloodwork. An echocardiogram did not show evidence of pulmonary hypertension. Given his history of a bone tumor resection, we obtained pathology results from the treating hospital which confirmed that the tumor was in fact an osteochondroma and not consistent with Langerhans cell histiocytosis.
He was treated with an inhaled corticosteroid and long-acting bronchodilator combination puffer. With desmopressin, his water intake reduced dramatically to 1-2 L/day. He presented again a year later with bilateral spontaneous pneumothoraces (left larger than right) and was treated with left-sided pleurodesis in the form of doxycycline. After a couple of relapses, he quit smoking after using varenicline and has remained smoke-free for 12 months at last follow-up. His latest FEV1 is 2.98 L (58% of predicted) with an FEV1/FVC ratio of 64%.