Familial paroxysmal dystonic choreoathetosis and response to alternate-day oxazepam therapy

The Dystonias

Dystonia is a difficult problem for both the clinician and the scientist. It is sufficiently common to be seen by almost all physicians, yet uncommon enough to prevent any physician from gaining broad experience in its diagnosis and treatment. Each case represents a difficult challenge even to the specialist. The basic scientist is faced with investigating a disorder that is without relevant animal models and which is so rare that obtaining suitable tissue for study is a major obstacle. Dystonia may be idiopathic, or associated with lesions from many sources, including a variety of rare diseases. If idiopathic, it may be genetically transmitted or sporadic. If genetically transmitted, it may be generalized or focal, with symptoms varying in different members of the same family. It may be refractory to treatment, or it may respond to any one of a number of individual drugs that have very different mechanisms of action. For idiopathic dystonias, no clear method of genetic transmission has been established and no consistent pathology identified.

Treatment of paroxysmal dyskinesias in children

OPINION STATEMENT

Paroxysmal dyskinesia represents a group of uncommon movement disorders that are characterized by episodes of abnormal movements arising from a baseline of normal or nearly normal movement. Recent advances in the genetics of these disorders have helped provide some unification of classification schemes and better understanding. However, the approach to treatment continues to be based on the phenotype more than the genotype. The treatment approach is primarily based on the factors that precipitate the episodes of abnormal movements. For paroxysmal kinesigenic dyskinesia (PKD) in which the spells are triggered by sudden movement, treatment with anticonvulsants that target voltage-sensitive sodium channels (e.g., carbamazepine or phenytoin) is highly effective. For paroxysmal nonkinesigenic dyskinesia (PNKD), treatment with benzodiazepines is effective in many patients. PNKD episodes are often precipitated by caffeine, ethanol, or sleep deprivation, and lifestyle modifications are often helpful. Paroxysmal exertion-induced dyskinesia (PED) is less likely to respond to medications, but the ketogenic diet or modified Atkins diet may provide benefit. As more knowledge is gained about the underlying biology of these disorders, additional treatments may emerge.

Paroxysmal Dyskinesia

This group of disorders is characterized by periodic sudden events of involuntary movement. The clinical range of these involuntary movements is wide including tonic spasms, choreiform and athetoid movements and sustained dystonic postures. Confusion with reflex forms of epilepsy has been common in the past, but in general, paroxysmal dyskinesias are not associated with alterations in consciousness or epileptiform activity on electroencephalogram. The underlying basis of the paroxysmal dyskinesia is under active investigation as is their relationship to epilepsy and other paroxysmal disorders.

Familial paroxysmal dystonic choreoathetosis revisited

A case of familial paroxysmal dystonic choreoathetosis (PDC) documented by video/EEG monitoring is described. The father of the proband is affected by exertional cramping but not PDC, lending support to the previous hypothesis that exertional cramping may represent a "forme fruste" or the incomplete expression of PDC. Other family members affected by PDC are women, with exercise-induced cramping alone found in two men. Two of the women report prolonged exertion as a precipitant of lengthy spells consistent with typical PDC rather than the previously described "intermediate," exercise-induced form of PDC. Exertional cramping in families affected by PDC may represent the variable expression of the "dystonia gene" in male members. Conversely, exercise-induced PDC, both of the intermediate and longer form described here, may have a predilection to manifest in women.

Intermittent clonazepam treatment prevents anticonvulsant tolerance in mice

The influence of intermittent benzodiazepine treatment on anticonvulsant tolerance was studied by comparing mice treated either daily or on alternate days with clonazepam, 0.25 mg/kg, i.p., administered twice a day. Tolerance was assessed by the ability of clonazepam to prevent pentylenetetrazol (PTZ) induced clonic convulsions. In mice treated daily with clonazepam, significant tolerance was evident after 5 days of treatment but did not increase further after 10 or 20 days of treatment. However, mice treated with clonazepam only on alternate days for 10 or 20 days showed no tolerance. Our data indicate that intermittent treatment may prevent development of tolerance to the anticonvulsant action of benzodiazepines.

Paroxysmal dystonic head tremor

Two patients with paroxysmal attacks of "no-no" direction head tremor and mild torticollis are described. One of them had the characteristic features of paroxysmal dystonic choreoathetosis and responded well to clonazepam.

Hereditary myoclonus and chorea: the spectrum of hereditary nonprogressive hyperkinetic movement disorders

We report three members of a single family who developed a newly described combination of myoclonus and chorea in association with mild ataxia. The occurrence of this and related syndromes suggests that inherited, slowly progressive myoclonus, chorea, and dystonia, alone or in combination, should be viewed as a spectrum of hyperkinetic involuntary movements, and that each motor component may represent variable expression of the same genetic defect.

Familial paroxysmal dystonic choreoathetosis: a family study

We interviewed and examined 12 members of a single family affected by paroxysmal dystonic choreoathetosis. Three subjects experienced characteristic painful dystonic spasms, often precipitated by cold and prolonged physical activity. Three other family members suffered painful cramping of their limbs, without involuntary movement, following physical exertion. Based on the clinical features of affected subjects, we suggest that exertional cramping may represent a "forme fruste" of paroxysmal dystonia.

Benzodiazepine receptor affinity alterations at physiologic temperature after chronic clonazepam exposure

Cerebral cortical cell cultures obtained from fetal mice were exposed to 200 nM clonazepam (CZP) for 14 days and benzodiazepine (BDZ) receptor binding was measured on intact cells in situ at 37 degrees C. Total, specific, and CZP-displaceable BDZ binding were significantly reduced from control values immediately after drug removal (77.7 +/- 1.4%, 75.1 +/- 3.0%, and 40.9 +/- 6.0% of control, respectively) but Ro5-4864-displaceable binding was not affected (87.6 +/- 5.1%). Binding returned to control values within 48 hours. Saturation analysis of the binding data indicated that a high-affinity binding site could not be detected in CZP-exposed cultures immediately after drug removal (162 nM versus 49 nM in controls, p less than .001), but was present 24 hours later.

Long-term exposure of cortical cell cultures to clonazepam reduces benzodiazepine receptor binding

To determine if reduced drug efficacy after long-term exposure to clonazepam may be a consequence of benzodiazepine receptor alterations, cerebral cortical cell cultures were exposed to the drug (200 nM) for 14 days. Receptor binding was assayed on living cells in situ. After drug exposure, binding in experimental cultures differed markedly from controls with respect to total, specific, and clonazepam-displaceable (neuronal) benzodiazepine binding (60%, 53%, and 6% of control values, respectively) but recovered within 96 h of drug removal. RO5-4864-displaceable (nonneuronal) binding was modestly reduced at 0 time (72% of control), but returned to control values in 24 h. The differences in binding could be attributable to a relatively reduced affinity of the high-affinity binding site (Kd approximately 18 nM for controls and approximately 30 nM for drug-exposed cultures) but not to changes in the low-affinity binding site or to reduced numbers of receptors.