A Rare Case of Malignant Syndrome in Parkinson's Disease Caused by Severe Dehydration and Complicated by Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH).

Malignant syndrome (MS) in Parkinson's disease (PD) is a rare complication that occurs in patients who have a history of PD and are taking dopaminergic drugs. The syndrome is quite similar to neuroleptic malignant syndrome (NMS) in presentation and is a potentially fatal syndrome. Awareness of symptoms, early diagnosis, and the ability to differentiate it from NMS is important to prevent mortality. Clinical manifestations of MS are similar to NMS and include altered mentation, rigidity, fever, leukocytosis, and elevated serum creatine kinase (CK). However, MS is differentiated from NMS by the precipitating factors; of which, the commonest precipitating factor for MS is dopaminergic drug withdrawal or dose reduction while other less common causes include infection, dehydration, and hot weather. We present a rare case of MS in a patient with a history of PD precipitated by severe dehydration and hot weather in the absence of dopaminergic drug withdrawal. He presented with fever, severe rigidity, altered mentation, dehydration, leukocytosis, and elevated CK. He was correctly diagnosed with MS and promptly treated, preventing mortality. The triad of fever, severe rigidity, and altered sensorium in a patient with a history of PD should prompt evaluation for MS in addition to NMS to initiate appropriate treatment and prevent mortality.