Background/Purpose: Shrinking lung syndrome (SLS) is a rare pulmonary manifestation of systemic lupus erythematosus (SLE) characterized by dyspnea, pleuritic chest pain, restriction on pulmonary function test (PFT), and signs of diaphragm dysfunction without evidence of significant pleuroparenchymal disease. We believe that lack of diagnostic criteria leads to misdiagnosis of SLS. Diagnosis of SLS requires careful evaluation of respiratory mechanics which includes spirometry, lung volumes, diffusion capacity, change in FEV1 (forced expiratory volume in one second) from sitting to supine, and consideration for specific diaphragm testing such as Sniff test, ultrasonography or electromyography (EMG). Careful consideration for mimickers of SLS such as obesity, pleural and central nervous system diseases should be considered since each has different management strategies. We report clinical, imaging and PFT characteristics of SLS in order to better understand the physiology seen in SLS and to increase awareness on this unsuspected entity.

Methods: We performed an electronic search of patients seen at the Cleveland Clinic between January 2005 – February 2017 with ICD-10 codes for SLE, restrictive lung disease, diaphragm dysfunction, or pleurisy. Clinical data were retrieved from the electronic medical records.

Results: Our search revealed 462 patients with SLE who had PFT results and a diagnostic code for restrictive lung disease, diaphragm dysfunction, or pleurisy. 38 of them were initially suspected to have SLS based on the opinion of their treating physician. Yet, only 27 patients had lung volumes (71%), and 20 had sitting/supine spirometry (53%). 35  had a chest X ray and/or computed tomography (92%). Sniff testing was performed in 7 cases, and showed abnormality in 70% of cases. EMG was done in  11 cases, and showed paresis/paralysis in 50% of cases. None had ultrasound of the diaphragm.

Ultimately, 8 out of 38 patients had a SLS diagnosis (Table). 30 patients had an alternative diagnosis including obesity (n=9), pleurisy (n=7), interstitial lung disease (n=4), severe pleural disease (n=4), asthma (n=2), emphysema (n=1), pneumonia (n=1) and rib fracture (n=1). 18 patients had a BMI ˃30 (47%), 5 had BMI ˃40 (13%). When present, lung volumes were useful to differentiate a restrictive pattern between diaphragm dysfunction and obesity related restriction. Diaphragmatic eventration and bibasilar infiltrates were the most common radiographic findings in SLS patients.

Conclusion: Our study showed that the majority of patients suspected with SLS had an alternative diagnosis. Almost one third of patients with suspected SLS did not have lung volumes or diaphragmatic function analysis done and almost half-of these patients did not have sitting/supine spirometry performed.  SLS is a diagnosis of exclusion and a comprehensive evaluation to exclude other reasons for a restrictive ventilatory defect is essential.