DYSKINESIA

    DEFINITION

    Movement disorder characterized by increased motor activity. 

    TOXIC CAUSES

    Amphetamines
    Anticholinergic agents
    Antihistamines
    Caffeine
    Cocaine
    Carbamazapine
    Carbon monoxide
    Levodopa
    Lithium
    Methylphenidate
    Nicotine
    Phencyclidine
    Phenytoin
    Tricyclic antidepressants

    Myoclonus is also observed as a feature of serotonin syndrome,
    associated with  pharmaceuticals which inhibit the re-uptake of
    serotonin: monoamine oxidase inhibitors, selective serotonin reuptake
    inhibitors, lithium, amitriptyline, pethidine, dextromethorphan,
    amphetamines, cocaine and lysergic diethylamide acid (LSD).

    NON-TOXIC CAUSES

    Degenerative:  Parkinson's disease
                   Alzheimer's disease

    Infective:     Neurosyphillis
                   Creutzfeld-Jacob disease

    Inherited:     Huntington's chorea
                   Benign essential tremor

    Metabolic:     Thyrotoxicosis
                   Wilson's disease

    Structural:    Cerebrovascular accidents
                   Tumour
                   Multiple sclerosis

    CLINICAL FEATURES

    Various types of dyskinesia are described:

         Chorea - continuous flow of irregular, jerking, explosive
         movements that flit from one part of the body to another in
         random sequence.

         Myoclonus - rapid shock-like muscle jerks, often repetitive. 

         Tremor - rhythmic sinusoidal movement. 

    DIFFERENTIAL DIAGNOSIS

    Alcohol withdrawal
    Anxiety states
    Cerebrovascular accidents
    Parkinsonism
    Pseudoseizures
    Shivering
    Rigors
    Sedative hypnotic withdrawal
    Seizures
    Tics

    RELEVANT INVESTIGATIONS

    Usually, no specific investigations are required to evaluate acute
    toxic dyskinesias.  Where indicated, the following may be useful: 

         Toxicology screens
         EEG or CT scan of head (to exclude seizures or central organic
           lesions)

    TREATMENT

    There is no specific treatment for toxic dyskinesia.  In severe cases,
    symptoms  can be alleviated by giving incremental doses of intravenous
    or oral  diazepam, carefully titrated to effect.   A suitable initial
    dose of diazepam is 0.1 mg/kg intravenously or 5 to 10 mg orally.

    CLINICAL COURSE AND MONITORING

    Acute toxic dyskinesias generally resolve along with resolution of the
    other clinical manifestation of the intoxication.  The patient should
    be carefully observed during this period.

    LONG-TERM COMPLICATIONS

    Long-term complications are unusual.  Patient should be followed to
    assess the response to the cessation of any therapeutic drugs.

    AUTHOR(S)/REVIEWERS

    Author:        Robert Dowsett
                   Consultant Toxicologist
                   Departments of Clinical Pharmacology and Emergency
                   Medicine
                   Westmead Hospital
                   Westmead, NSW 2145
                   Australia

    Reviewers:     London 3/98: P. Dargan, T. Della Puppa, L. Murray,
                   A. Nantel, M. Nicholls.