Med/Psych Update

Differentiating serotonin syndrome and neuroleptic malignant syndrome

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

References

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Clinical presentation. Patients with NMS typically present with a tetrad of symptoms: mental status changes, muscular rigidity, hyperthermia, and autonomic instability.¹² Mental status changes can include confusion and agitation, as well as catatonic signs and mutism. The muscular rigidity of NMS is characterized by “lead pipe rigidity” and may be accompanied by tremor, dystonia, or dyskinesias. Laboratory findings include elevated serum CK (from severe rigidity), often >1,000 U/L, although normal levels can be observed if rigidity has not yet developed.¹³

Treatment. The first step for treatment is to discontinue the causative medication.¹⁴ Initiate supportive therapy immediately to restrict the progression of symptoms. Interventions include cooling blankets, fluid resuscitation, and antihypertensives to maintain autonomic stability¹⁵ or benzodiazepines to control agitation. In severe cases, muscular rigidity may extend to the airways and intubation may be required. The severity of these symptoms may warrant admission to the ICU for close monitoring. Pharmacologic treatment with dantrolene (a muscle relaxant that blocks calcium efflux from the sarcoplasmic reticulum) and bromocriptine (a dopamine agonist) have been utilized.¹⁴ In case reports, electroconvulsive therapy (ECT) has been used to treat NMS^15,16; however, prospective research comparing ECT with traditional treatment has not been conducted. It is also worth mentioning that if a clinician wishes to restart the neuroleptic medication, a 2-week washout period will minimize the risk of NMS recurrence.¹⁷

Differentiating between SS and NMS

Differentiating between these 2 syndromes (Table 4¹⁷) is critical to direct appropriate intervention. Table 5¹⁷ outlines the treatment overview for SS and NMS.

Detailed history. A detailed history is imperative in making accurate diagnoses. Useful components of the history include a patient’s duration of symptoms and medication history (prescription medications as well as over-the-counter medications, supplements, and illicit drugs). Also assess for medical comorbidities, because certain medical diagnoses may alert the clinician that it is likely the patient had been prescribed serotonergic agents or neuroleptics, and renal or liver impairment may alert the clinician of decreased metabolism rates. Medication history is arguably the most useful piece of the interview, because serotonergic agents can cause SS, whereas dopamine blockers cause NMS. It should be noted that excess serotonin acts as a true toxidrome and is concentration-dependent in causing SS, whereas NMS is an idiosyncratic reaction to a drug.

Physical exam. Although there are many overlapping clinical manifestations, SS produces neuromuscular hyperactivity (ie, clonus, hyperreflexia), whereas NMS is characterized by more sluggish responses (ie, rigidity, bradyreflexia).¹⁸

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Differentiating serotonin syndrome and neuroleptic malignant syndrome

References

Differentiating between SS and NMS

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