A Case Report on Serotonin Syndrome in a Patient With Parkinson’s Disease: Diagnostic and Management Challenges

Patients with Parkinson's disease are often at risk of polypharmacy, which can lead to serious medication side effects and interactions. Serotonin syndrome (SS) can develop in this patient population due to a possible drug-drug interaction between antidepressants and antiparkinson drugs with serotoninergic activity. On the other hand, these patients are also at risk of malignant syndrome (MS) secondary to dopaminergic medication withdrawal. In this case report, we present a 71-year-old female with Parkinson's disease who developed symptoms suggestive of SS. The patient was admitted to the medical intensive care unit at the Institute for Pulmonary Diseases of Vojvodina in the Republic of Serbia due to impaired consciousness and a previously witnessed cardiorespiratory arrest. Her chronic antiparkinson medication regimen consisted of levodopa, benserazide, entacapone, ropinirole, and rasagiline. Furthermore, she had been prescribed duloxetine for a remote history of depression, which she had only been taking intermittently. Several days before admission, however, the patient started taking duloxetine again due to low mood. Upon admission, laboratory tests revealed leukocytosis with neutrophilia, elevated C-reactive protein, procalcitonin, lactate, urea, and creatinine. Serum creatine kinase (CK) levels were also elevated at 1250 U/L. Six hours after admission to the ICU, the patient developed hyperthermia, hyperreflexia, spontaneous myoclonus, and tremors. Her CK levels continued to rise, reaching 6900 U/L, and her renal function worsened. Due to the possibility of either SS or MS, external cooling measures with frozen gel packs were administered, resulting in the patient's stabilization over a few hours. Further, serotoninergic medication (rasagiline and duloxetine) was discontinued. On the fifth day of hospitalization, a head CT showed signs of cytotoxic edema. On the 11th day, the patient became hemodynamically unstable and passed away despite all adequate resuscitative measures. The purpose of this case report is to raise awareness of possible SS in patients taking monoamine oxidase-B (MAO-B) inhibitors such as rasagiline. Clinicians should have a high index of suspicion for this complication, especially in patients who are treated for comorbid depression with serotoninergic drugs. Furthermore, we emphasize the importance of correctly differentiating SS from MS, which are both risks for patients with Parkinson's disease. A correct approach to these patients is of utmost importance for adequate management and optimal outcomes.