The differential diagnosis of<unk>  is extensive as signs and symptoms of<unk>  may overlap significantly with those of other conditions. Therefore, a careful and detailed history, medication review, and physical exam are key to diagnosing<unk>  and differentiating it from other conditions. Furthermore, some of these conditions can themselves lead to<unk> . The differential diagnosis is as follows: *Neuroleptic malignant syndrome (NMS) and<unk>  are both life-threatening conditions that share many of the same characteristics including fever, autonomic instability, rigidity, and delirium. Lab values of low serum iron, elevated creatine kinase, and white blood cell count are also shared by the two disorders further complicating the diagnosis. There are features of malignant<unk>  (posturing, impulsivity, etc.) that are absent from NSM and the lab results are not as consistent in malignant<unk>  as they are in NMS. Some experts consider NMS to be a drug-induced condition associated with antipsychotics, particularly, first generation antipsychotics, but it has not been established as a subtype. Therefore, discontinuing antipsychotics and starting benzodiazepines is a treatment for this condition, and similarly it is helpful in<unk>  as well. *Anti-NMDA receptor encephalitis is an autoimmune disorder characterized by neuropsychiatric features and the presence of IgG antibodies. The presentation of anti-NMDAR encephalitis has been categorized into 5 phases: prodromal phase, psychotic phase, unresponsive phase, hyperkinetic phase, and recovery phase. The psychotic phase progresses into the unresponsive phase characterized by mutism, decreased motor activity, and<unk> . *Both Serotonin syndrome and malignant<unk>  may present with signs and symptoms of delirium, autonomic instability, hyperthermia, and rigidity. Again, similar to the presentation in NSM. However, patients with Serotonin syndrome have a history of ingestion of serotonergic drugs (Ex: SSRI). These patients will also present with hyperreflexia, myoclonus, nausea, vomiting, and diarrhea. *Malignant hyperthermia and malignant<unk>  share features of autonomic instability, hyperthermia, and rigidity. However, malignant hyperthermia is a hereditary disorder of skeletal muscle that makes these patients susceptible to exposure to halogenated anesthetics and/or depolarizing muscle relaxants like succinylcholine. Malignant hyperthermia most commonly occurs in the intraoperative or postoperative periods. Other signs and symptoms of malignant hyperthermia include metabolic and respiratory acidosis, hyperkalemia, and cardiac arrhythmias. *Akinetic mutism is a neurological disorder characterized by a decrease in goal-directed behavior and motivation; however, the patient has an intact level of consciousness. Patients may present with apathy, and may seem indifferent to pain, hunger, or thirst. Akinetic mutism has been associated with structural damage in a variety of brain areas. Akinetic mutism and<unk>  may both manifest with immobility, mutism, and waxy flexibility. Differentiating both disorders is the fact that akinetic mutism does not present with echolalia, echopraxia, or posturing. Furthermore, it is not responsive to benzodiazepines as is the case for<unk> . *Elective mutism has an anxious etiology but has also been associated with personality disorders. Patients with this disorder fail to speak with some individuals but will speak with others. Likewise, they may refuse to speak in certain situations; for example, a child who refuses to speak at school but is conversational at home. This disorder is distinguished from<unk>  by the absence of any other signs/symptoms. *Nonconvulsive status epilepticus is seizure activity with no accompanying tonic-clonic movements. It can present with stupor, similar to<unk> , and they both respond to benzodiazepines. Nonconvulsive status epilepticus is diagnosed by the presence of seizure activity seen on electroencephalogram (EEG).<unk>  on the other hand, is associated with normal EEG or diffuse slowing. *Delirium is characterized by fluctuating disturbed perception and consciousness in the ill individual. It has hypoactive and hyperactive or mixed forms. People with hyperactive delirium present similarly to those with excited<unk>  and have symptoms of restlessness, agitation, and aggression. Those with hypoactive delirium present with similarly to retarded<unk> , withdrawn and quiet. However,<unk>  also includes other distinguishing features including posturing and rigidity as well as a positive response to benzodiazepines. *Patients with locked-in syndrome present with immobility and mutism; however, unlike patients with<unk>  who are unmotivated to communicate, patients with locked-in syndrome try to communicate with eye movements and blinking. Furthermore, locked-in syndrome is caused by damage to the brainstem. *Stiff-person syndrome and<unk>  are similar in that they may both present with rigidity, autonomic instability and a positive response to benzodiazepines. However, stiff-person syndrome may be associated with anti-glutamic acid decarboxylase (anti-GAD) antibodies and other<unk>  signs such as mutism and posturing are not part of the syndrome. *Untreated late-stage Parkinson's disease may present similarly to retarded<unk>  with symptoms of immobility, rigidity, and difficulty speaking. Further complicating the diagnosis is the fact that many patients with Parkinson's disease will have major depressive disorder, which may be the underlying cause of<unk> . Parkinson's disease can be distinguished from<unk>  by a positive response to levodopa.<unk>  on the other hand will show a positive response to benzodiazepines.
Catatonia
Neuroleptic malignant syndrome
Paratonia
Childhood schizophrenia
Cataplexy
Clonus
Catalepsy
Psychomotor agitation