The presence of a movement disorder may help identify the cause of poisoning.
- Involuntary motor restlessness renders the patient unable to remain still and may resemble psychotic agitation.
- A history of increasing medication dose may help identify akathisia.
- Toxic causes include the use of neuroleptic, antiemetic, sympathomimetic, or antiparkinsonian medications.
- Transient loss of postural tone in a muscle group results in jerking movements as tone is regained.
- It is difficult to distinguish these entities on examination: myoclonus results from contractions, and asterixis results from loss of tone in a muscle group.
- Medications causing asterixis and myoclonus include anticonvulsant, sedative-hypnotic, and cyclic antidepressant medications.
- Other toxic causes include lead or mercury exposures; a history of exposure and a urinary metal testing may reveal the cause.
- Nontoxic causes include metabolic encephalopathy, hepatic or renal failure, hyperosmolarity, or anoxia.
- This disorder involves loss of muscular coordination (e.g., an inability to maintain an upright posture while standing or attempting to walk in a straight line).
- Common toxic causes include ethanol, sedative-hypnotic agents, anticonvulsants, cyclic antidepressants, selective serotonin reuptake inhibitors (SSRIs), or antihistamine medications.
- Nontoxic causes include somnolence from various causes and sensory neuropathy.
- Alcoholic cerebellar degeneration may exacerbate ataxia resulting from other causes.
- This involves a variety of sudden erratic random limb movements, often described as "waving" or, when movements are forceful, "ballismus."
- Medication causes include sedative-hypnotic, antihistamine, cyclic antidepressant, anticonvulsant, anti-parkinsonian, sympathomimetic, opioid, neuroleptic, and steroid medications.
- Other toxic causes include carbon monoxide, toluene, lithium, manganese, or thallium; the serum lithium level may be elevated, and the results of urine tests for manganese or thallium may show elevated levels.
- Metabolic causes include hyper- or hypoglycemia, hyper- or hyponatremia, hypocalcemia, hypomagnesemia, hyperthyroidism, and thiamine deficiency.
- Neurologic diseases include Huntington's chorea and Wilson's disease.
- This term covers a variety of movement disorders due to muscle spasm: blepharospasm, dysarthria, dysphagia, involuntary tongue movements, oculogyric crisis, opisthotonos, retrocollis, and torticollis.
- It usually involves the head and neck and only rarely involves the trunk or airway.
- Toxic causes include neuroleptic, antiemetic, or anti-parkinsonian drugs.
- Neuroleptics and antiemetics are the most common medications that cause dystonia.
- This disorder, slurred speech, results from poor control of the speech muscles.
- Toxic causes include sedative-hypnotic agents, anticonvulsants, cyclic antidepressants, SSRIs, antihistamines, and many other medications.
- Spasm of the fibers in a single motor unit of a muscle results in discrete twitching.
- Medication causes include sympathomimetic, cholinergic, and hypoglycemic drugs.
- Other toxic causes include a variety of animal venoms, strychnine, lithium, lead, mercury, or manganese.
- Nontoxic causes. Fatigue and cold may result in fasciculation.
- Pathologic fasciculation may result from a variety of neurologic disorders that affect the motor nerve.
- Rapid eye movements appear to jerk the eyes in a given direction after a slow component in the opposite direction.
- Toxic causes include sedative-hypnotic agents, phencyclidine (PCP), lithium, anticonvulsants, and several other medications.
- A variety of neurologic causes such as intracranial lesions or labyrinthitis may cause nystagmus.
- This disorder is characterized by tremor, rigidity (classically cogwheel type), slow movements, and postural instability.
- Lack of facial expression, shuffling gait, drooling, and micrographia also may be seen both with Parkinson's disease and following toxic insults that may result in a parkinsonian syndrome.
- Toxic causes include MPTP (methyl-gamma-phenyl-1,2,3,6, tetrahydropyridine), which destroys the substantia nigra, resulting in parkinsonism.
- Medication causes. Parkinsonism also may result from the use of a number of drugs that antagonize dopamine: neuroleptic, alphamethyldopa, metoclopramide, prochlorperazine, reserpine, and tetrabenazine medications.
- Other toxic causes. Parkinsonism also may occur as sequelae of toxicity from carbon disulfide, carbon monoxide, cyanide, methanol, or manganese.
See also SECTION II, NMS and Serotonin Syndrome chapter.
- Malignant hyperthermia, neuroleptic malignant syndrome (NMS), and serotonin syndrome are characterized by muscle rigidity, fever, altered mental status, and autonomic dysfunction; tremor, dystonia, and chorea also may occur.
- Toxic causes include monoamine oxidase (MAO) inhibitor overdose or food or drug interaction with MAO inhibitors; these may be indistinguishable from NMS except by drug history.
- Similar syndromes include heat stroke, catatonia, and infection.
Tardive dyskinesia is not an uncommon complication of neuroleptic therapy. It is felt to be due to upregulation of dopamine receptors. Tardive dyskinesia commonly manifests as lip smacking, facial movements, or tongue protrusion. It can occur with changing doses or withdrawal of therapy. It is often not reversible. Anticholinergic agents may worsen symptoms. Toxic causes include phenothiazines and butyrophenones. Tardive dystonia is a delayed complication of the chronic use of neuroleptic, metoclopramide, or anti-parkinsonian drugs.