Acetazolamide responsive hereditary paroxysmal ataxia

The therapeutic mode of action of 4-aminopyridine in cerebellar ataxia

Episodic ataxia type 2 (EA2) is a hereditary cerebellar ataxia associated with mutations in the P/Q-type voltage-gated calcium (Ca(2+)) channels. Therapeutic approaches for treatment of EA2 are very limited. Presently, the potassium (K(+)) channel blocker 4-aminopyridine (4-AP) constitutes the most promising treatment, although its mechanism of action is not understood. Here we show that, in contrast to what is commonly believed, therapeutic concentrations of 4-AP do not increase the inhibitory drive of cerebellar Purkinje cells. Instead, 4-AP restores the severely diminished precision of pacemaking in Purkinje cells of EA2 mutant mice by prolonging the action potential and increasing the action potential afterhyperpolarization. Consistent with this mode of action, the therapeutic efficacy of 4-AP was comparable, and not additive, to chlorzoxazone, an activator of Ca(2+)-dependent K(+) channels that also restores the precision of Purkinje cell pacemaking. The likely target of 4-AP at the concentrations used are the K(v)1 family of K(+) channels, possibly the K(v)1.5 subtype. Because at higher concentrations 4-AP blocks a large array of K(+) channels and is a proconvulsant, use of selective K(v)1 channel blockers is likely to be a safer substitute for treatment of cerebellar ataxia.

Phosphorus and proton magnetic resonance spectroscopy in episodic ataxia type 2

Localized phosphorus (31P) and proton (1H) magnetic resonance spectroscopy was performed in the cerebellum and the occipital lobe of 6 patients with episodic ataxia type 2. From use of 31P magnetic resonance spectroscopy, untreated patients showed decreased high-energy phosphate ratios in the cerebrum, and increased pH in the cerebellum and cerebrum, which normalized under acetazolamide. 1H magnetic resonance spectra demonstrated high lactate peaks in 3 of the 6 patients. These metabolic alterations, probably induced by the calcium channelopathy, may characterize episodic ataxia type 2.

The electroencephalogram in acetazolamide-responsive periodic ataxia

Acetazolamide-responsive periodic ataxia (ARPA) is a rare movement disorder, characterized by recurrent episodes of vertigo, cerebellar ataxia, and nystagmus, which has recently been characterized genetically. The pathophysiology is unknown, but it is probably not epileptic. By definition, acetazolamide produces an impressive symptomatic relief. Because of the paroxysmal nature of the disorder, EEG tracings were often obtained. We report four new cases (two familial and two sporadic) with typical ARPA (none of whom had metabolic abnormalities or continuous electrical muscle activity) and review the EEG findings associated with this disorder. EEG findings were reported in 18 kindreds and nine sporadic cases (including ours). EEG was described in 54 of the 140 affected cases and was abnormal in 52% (28/54). Most commonly seen was intermittent generalized slow activity, observed in 35% (19/54), frequently intermingled with spikes (10 cases). Other abnormalities included nonspecific mild generalized or focal slowing in seven (13%) and focal epileptic activity in two (4%) patients. The paroxysmal EEG activity frequently seen in ARPA should not establish a diagnosis of epilepsy. Although not specific, it may suggest the correct diagnosis and indicate treatment with acetazolamide.

EEG findings in acetazolamide-responsive hereditary paroxysmal ataxia

EEG studies were performed in six family members affected by acetazolamide-responsive paroxysmal ataxia. Intermittent rhythmic delta activity was found at rest in five of them; low amplitude spikes were associated with delta waves in two cases, resulting in irregular spike and wave patterns. Slowing of background activity was present in three patients. EEG abnormalities were activated by hyperventilation and modified neither by intermittent photic stimulation, nor by acetazolamide therapy. Our results suggest that EEG may be helpful to recognize this rare, but well defined, treatable disorder.

Familial paroxysmal ataxia: report of a family

Three cases from one kindred who suffer from dominant paroxysmal ataxia are described. This is a rare benign non-progressive disorder of childhood onset, characterised by bouts of ataxia with abrupt onset lasting minutes or hours. Cases may be identified on the basis of a suggestive history, nystagmus persisting between episodes, and dominant inheritance. Treatment with acetazolamide is often dramatically effective. This family is thought to be the first described in the UK but many more probably exist, mislabelled as epilepsy or migraine.

Familial periodic cerebellar ataxia: a problem of cerebellar intracellular pH homeostasis

Six affected members of two families with familial periodic cerebellar ataxia were relieved of their symptoms with oral acetazolamide. Phosphorus 31 (31P) nuclear magnetic resonance spectroscopy showed abnormal intracellular pH levels in the cerebellum of all subjects when they were not treated. These levels returned to normal with treatment. Cerebral pH values were also measured in one family and were normal before and after treatment. An additional 3 patients with similar attacks, but without a family history, had normal untreated pH values in the cerebellum and cerebrum.

Persistent superior oblique paresis as a manifestation of familial periodic cerebellar ataxia

A brother and sister complained of persistent diplopia due to superior oblique palsies. The cause of their symptoms became apparent when they were diagnosed as having familial periodic cerebellar ataxia (FPCA), a rare autosomal dominant condition. Oral acetazolamide (250 mg twice daily) not only prevented all the periodic symptoms but also relieved their diplopia, which had been present between attacks.

Hereditary paroxysmal ataxia with neuromyotonia

The clinical manifestations of a patient with hereditary paroxysmal ataxia and neuromyotonia are described. Generalized tremor, triggered by sudden movements, and spasms of hand and foot muscles were the main clinical findings. Electromyogram (EMG) and nerve blocking studies led to the diagnosis of neuromyotonia. Treatment with acetozolamide was of no therapeutic value, confirming previous observations about the difference in response of paroxysmal ataxia with and without neuromyotonia.