Pleural effusion associated with long-term dantrolene administration in three patients with severe motor and intellectual disabilities

Chronic unilateral pleural effusion developed in three patients with severe motor and intellectual disabilities. All patients received 5-15 years of dantrolene administration for their spasticity. The cause of pleural effusion was indistinct, despite close investigations for etiologies such as infection or tumor. The pleural fluid consisted of sterile exudate in all patients. One patient had eosinophilia in his pleural fluid, while peripheral blood eosinophilia was seen in the other two. The pleural biopsy and autopsy specimens revealed only non-specific inflammatory findings. After dantrolene therapy was discontinued, pleural effusion almost disappeared in two patients in the following several months, but the other died of multi-organ failure from another underlying disease. It is important to take chemical pleurisy into consideration when dealing with pleural effusion of unknown etiology. Moreover, respiratory side effect should be examined in patients treated with chronic dantrolene administration.