Med/Psych Update

Differentiating serotonin syndrome and neuroleptic malignant syndrome

Current Psychiatry. 2019 February;18(2):30-36

References

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Management pitfalls include misdiagnosis of SS, failure to recognize its rapid rate of progression, and adverse effects of pharmacologic therapy.³ The most effective treatment for SS is prevention. SS can be prevented by astute pharmacologic understanding, avoidance of polypharmacy, and physician education.³

Neuroleptic malignant syndrome

Possible mechanisms. Neuromuscular malignant syndrome is thought to result from dopamine receptor antagonism leading to a hypodopaminergic state in the striatum and hypothalamus.⁸ The pathophysiology behind NMS has not fully been elucidated; however, several hypotheses attempt to explain this life-threatening reaction. The first focuses on dopamine D2 receptor antagonism, because many of the neuroleptic (antipsychotic) medications that can precipitate NMS are involved in dopamine blockade. In this theory, blocking dopamine D2 receptors in the anterior hypothalamus explains the hyperthermia seen in NMS, while blockade in the corpus striatum is believed to lead to muscle rigidity.⁹

The second hypothesis suggests that neuroleptics may have a direct toxic effect to muscle cells. Neuroleptics influence calcium transport across the sarcoplasmic reticulum and can lead to increased calcium release, which may contribute to the muscle rigidity and hyperthermia seen in NMS.⁹

The third hypothesis involves hyperactivity of the sympathetic nervous system; it is thought that psychologic stressors alter frontal lobe function, with neuroleptics disrupting the inhibitory pathways of the sympathetic nervous system. The autonomic nervous system innervates multiple organ systems, so this excessively dysregulated sympathetic nervous system may be responsible for multiple NMS symptoms (hyperthermia, muscle rigidity, hypertension, diaphoresis, tachycardia, elevated CK.¹⁰

NMS can be caused by neuroleptic agents (both first- and second-generation antipsychotics) as well as antiemetics (Table 3¹). The time between use of these medications and onset of symptoms is highly variable. NMS can occur after a single dose, after a dose adjustment, or possibly after years of treatment with the same medication. It is not dose-dependent.¹¹ In certain individuals, NMS may occur at therapeutic doses.