Symptoms include muscle stiffness (lead pipe rigidity), cogwheel rigidity, shuffling gait, stooped posture, and drooling. The pill-rolling tremor of idiopathic parkinsonism is rare, but a regular, coarse tremor similar to essential tremor may be present. The so-called rabbit syndrome is a tremor affecting the lips and perioral muscles and is another parkinsonian effect seen with antipsychotics, although perioral tremor is more likely than other tremors to occur late in the course of treatment.

Parkinsonian adverse effects occur in about 15% of patients who are treated with antipsychotics, usually within 5 to 90 days of the initiation of treatment. Patients who are elderly and female are at the highest risk for neuroleptic-induced parkinsonism, although the disorder can occur at all ages.

Caused by the blockade of dopamine type 2 (D₂) receptors in the caudate at the termination of the nigrostriatal dopamine neurons. All antipsychotics can cause the symptoms, especially high-potency drugs with low levels of anticholinergic activity (e.g., trifluoperazine [Stelazine]). Chlorpromazine (Thorazine) and thioridazine (Mellaril) are not likely to be involved. The newer, atypical antipsychotics (e.g., aripiprazole [Abilify], olanzapine [Zyprexa], and quetiapine [Seroquel]) are less likely to cause parkinsonism.

Includes idiopathic parkinsonism, other organic causes of parkinsonism, and depression, which can also be associated with parkinsonian symptoms.

Can be treated with anticholinergic agents, benztropine (Cogentin), amantadine (Symmetrel), or diphenhydramine (Benadryl) (Table 31-2). Anticholinergics should be withdrawn after 4 to 6 weeks to assess whether tolerance to the parkinsonian effects has developed;
about half of patients with neuroleptic-induced parkinsonism require continued treatment. Even after the antipsychotics are withdrawn, parkinsonian symptoms may last for up to 2 weeks and even up to 3 months in elderly patients. With such patients, the clinician may continue the anticholinergic drug after the antipsychotic has been stopped until the parkinsonian symptoms resolve completely.

Dystonias are brief or prolonged contractions of muscles that result in obviously abnormal movements or postures, including oculogyric crises, tongue protrusion, trismus, torticollis, laryngeal–pharyngeal dystonias, and dystonic postures of the limbs and trunk. Other dystonias include blepharospasm and glossopharyngeal dystonia; the latter results in dysarthria, dysphagia, and even difficulty in breathing, which can cause cyanosis. Children are particularly likely to
evidence opisthotonos, scoliosis, lordosis, and writhing movements. Dystonia can be painful and frightening and often results in noncompliance with future drug treatment regimens.

The development of dystonic symptoms is characterized by their early onset during the course of treatment with neuroleptics and their high incidence in men, in patients younger than age 30, and in patients given high dosages of high-potency medications.

Although it is most common with intramuscular doses of high-potency antipsychotics, dystonia can occur with any antipsychotic. It is least common with thioridazine and is uncommon with atypical antipsychotics. The mechanism of action is thought to be dopaminergic hyperactivity in the basal ganglia that occurs when central nervous system (CNS) levels of the antipsychotic drug begin to fall between doses.

Includes seizures and tardive dyskinesia.

Dystonia can fluctuate spontaneously and respond to reassurance so that the clinician acquires the false impression that the movement is hysterical or completely under conscious control.

Prophylaxis with anticholinergics or related drugs (Table 31-2) usually prevents dystonia, although the risks of prophylactic treatment weigh against that benefit. Treatment with intramuscular anticholinergics or intravenous or intramuscular diphenhydramine (50 mg) almost
always relieves the symptoms. Diazepam (Valium) (10 mg intravenously), amobarbital (Amytal), caffeine sodium benzoate, and hypnosis have also been reported to be effective. Although tolerance for the adverse effect usually develops, it is sometimes prudent to change the antipsychotic if the patient is particularly concerned that the reaction may recur.