Tardive Dystonia

Etiology

The precise pathophysiological mechanism of tardive dystonia is unknown.[6] It is generally accepted that dopaminergic antagonism leads to excessive compensatory activity, resulting in dystonia as the inciting drug is metabolized and diluted. Some postulate that dystonia is simply the result of excessive dopamine blockade.[3] Either mechanism includes the involvement of the nigrostriatal tract. It is believed that aberrant dopaminergic activity within the basal ganglia, subsequently leads to extrapyramidal symptoms. The medications that cause this dopamine receptor blocking are neuroleptics. Apart from these antipsychotics, other dopamine antagonists have also been implicated.[3]

Epidemiology

Acute and tardive dystonic reactions occur less frequently than other related EPS manifestations, such as Parkinson's-like symptoms and akathisia. There is some debate regarding the chances of developing tardive dystonia, with studies suggesting it is somewhere between <1 to 2%  of patients taking antipsychotics.[7] Risk factors include age, males, previous history of dystonic reactions, cocaine use, electrolyte abnormalities, and dehydration.[8] Consistent across most studies is the predominance of young males developing tardive dystonia more frequently. It is possible this sex difference is merely a reflection of the earlier age of onset of schizophrenia in males.[4] 

One study revealed the interval between the age at first exposure to the neuroleptic and the age at onset of tardive dystonia ranged from four days to twenty-three years, with a mean of about six years. In this same study, researchers noted that younger patients experienced a shorter interval from neuroleptic exposure to symptom presentation.[4] Similarly, those who experienced the onset of dystonia at a younger age experienced more rapid symptom progression.

History and Physical

Tardive dystonia often has an insidious and progressive presentation. Although associated with a latent and thus “tardive” onset, the presentation may occur anywhere from days to years following initial exposure to dopamine receptor antagonism. Patients have reported that unusual sensory symptoms, along with strange somatic sensations, have preceded the onset of tardive dystonia. For example, neck pain has been found to precede the onset of cervical dystonia. Furthermore, research has determined that the development of tardive manifestations presents as focal dystonia, most notably torticollis or blepharospasm, followed by pharyngeal dystonia, oromandibular dystonia, and dystonia of the lips and tongue.

Dystonias of the arms, legs, and trunk are less frequent. On examination, pharyngeal dystonia will present as dysphagia, whereas oromandibular dystonia may present as a severe speech disturbance.[4] Tardive dystonia will less often occur focally and instead tends to distribute more diffusely.

Evaluation

Prompt recognition and subsequent intervention are paramount in the setting of tardive dystonia. Proper evaluation begins with reviewing the primary diagnosis, describing the precipitating motor abnormalities, assessing symptom severity, and finally, by developing a treatment plan based upon the specific phenomenology. It is important that the clinician review the full medical profile, as alternative dopaminergic antagonizing medications have been known to induce tardive syndromes. Such inciting agents include dopamine receptor blocking anti-emetics, including prochlorperazine, metoclopramide, and promethazine.[9]

Treatment / Management

Upon the proper identification of tardive dystonia, the offending agent(s) should be modified and if possible, discontinued. Clinical judgment will indicate whether abrupt cessation or a gradual taper is most appropriate. Some experts suggest simply cross-tapering to an alternative antipsychotic with a lower EPS profile, such as clozapine.

Drug-induced EPS are believed to precipitate following the blockade of nigrostriatal dopamine tracts, ultimately resulting in an increased ratio of cholinergic to dopaminergic activity. Therefore, drugs that antagonize cholinergic activity and increase striatal dopaminergic function will theoretically normalize the biochemical imbalance.[10]

One study reviewed the therapeutic efficacy of specific pharmacologic interventions and revealed “at least some benefit” in 53% of patients following the administration of tetrabenazine, 44% with anticholinergic agents, 56% with benzodiazepines, and 56% with baclofen.[4] The most robust therapeutic effects were experienced following botulin toxin administration, where 83% of patients endorsed “considerable relief.”[4] Other therapeutic agents to consider include L-dopa, dopamine agonists, amantadine, beta-blockers, anticonvulsants, choline, and vitamin E.(B3)

Differential Diagnosis

The list of differential diagnoses for tardive dystonia is extensive and includes primary and secondary etiologies of dystonias. Secondary forms of dystonia include metabolic abnormalities, toxic states, neurodegenerative disorders, and structural abnormalities of the brain.[11]

Drug-induced dystonic syndromes can be distinguished by acknowledging a history of neuroleptic treatment, negative family history of primary dystonia, and the absence of associated neurological signs. It is not uncommon for patients on chronic neuroleptics to present with tardive syndromes. Furthermore, patients can experience more than one of these tardive syndromes simultaneously, further complicating matters. These latent motor abnormalities can be further subdivided into three major subtypes, including tardive dyskinesia, tardive dystonia, and tardive akathisia.

Tardive dyskinesia is characterized by truncal, appendicular, or orobuccolingual choreiform movements; whereas tardive dystonia manifests as stereotyped twisting and turning muscle spasms. Tardive dyskinesia also tends to have a later age of onset than tardive dystonia.[4] One study found the mean age of onset of tardive dyskinesia in a research group to be 57 years old and that of tardive dystonia to be 37 years old.[9] Tardive akathisia shares less in common with its two sister tardive syndromes and is defined as an unpleasant inner sense of restlessness or unease, ultimately indistinguishable from acute akathisia.

Prognosis

Once established, the progression of the dystonia tends to evolve in a stepwise fashion over months to years, with subsequent involvement of additional body parts. Studies reveal that progression to maximum intensity and distribution occurs within 2 years from onset. More rapid progression has been noted in the population with a younger age at onset.[4] Tardive syndromes can be a source of intense distress and potential disability. Unfortunately, these syndromes can be permanent, even after the discontinuation of the offending agent.[9] 

One study attempted to demarcate outcome groups based upon symptom resolution following treatment. In this study of 107 patients being treated for tardive dystonia, 14% were in remission, 39% were improved, and 50% noted either no improvement or exacerbating symptomatology.[4] Within this cohort, those who discontinued their neuroleptic were more likely to have experienced symptom remission. More specifically, those who discontinued antipsychotics more rapidly benefitted from a higher likelihood of remission.[4] Remission was reached within a mean of 2.4 years from the discontinuation of all neuroleptic agents.[4] Furthermore, dystonia appears irreversible in those exposed to neuroleptics for greater than 10 years.

Complications

The severity of tardive dystonia ranges on a spectrum from imperceptible to frank disability. Subtle impairments include muscle tightness and cramps, leading to mastication and speech discomfort. More intense complications include oculogyric crisis, dysphagia, dysarthria, as well as lethal respiratory stridor. In severe instances, dystonic reactions can induce apnea, leading to fatality. Less common complications include dystonic involvement of axial, limb, and truncal muscle groups leading to Pisa syndrome, camptocormia, and opisthotonus.[3]