Contractures, continuous muscle discharges, and titubation

Fasciculations in Children

Fasciculations are the most common form of spontaneous muscle contraction. They frequently occur in healthy individuals. However, there are a minority of situations that fasciculations are observed in association with specific neurologic disorders. Publications concerning the evaluation of pediatric patients experiencing fasciculations are limited. These children may undergo invasive or expensive diagnostic investigations that are unnecessary. Moreover, without careful consideration of differential diagnoses, rare neuromuscular disorders that present with fasciculations in the pediatric age group can be under-recognized by pediatric neurologists. This review examines the most important pediatric disorders presenting with fasciculations and other spontaneous muscle contractions to guide pediatric neurologists in evaluating these children.

Paroxysmal Genetic Movement Disorders and Epilepsy

Paroxysmal movement disorders include paroxysmal kinesigenic dyskinesia, paroxysmal non-kinesigenic dyskinesia, paroxysmal exercise-induced dyskinesia, and episodic ataxias. In recent years, there has been renewed interest and recognition of these disorders and their intersection with epilepsy, at the molecular and pathophysiological levels. In this review, we discuss how these distinct phenotypes were constructed from a historical perspective and discuss how they are currently coalescing into established genetic etiologies with extensive pleiotropy, emphasizing clinical phenotyping important for diagnosis and for interpreting results from genetic testing. We discuss insights on the pathophysiology of select disorders and describe shared mechanisms that overlap treatment principles in some of these disorders. In the near future, it is likely that a growing number of genes will be described associating movement disorders and epilepsy, in parallel with improved understanding of disease mechanisms leading to more effective treatments.

Paroxysmal movement disorders - practical update on diagnosis and management

Introduction: Paroxysmal dyskinesias and episodic ataxias are often caused by mutations in genes related to cell membrane and synaptic function. Despite the exponential increase in publications of genetically confirmed cases, management remains largely clinical based on non-systematic evidence. Areas covered: The authors provide a historical and clinical review of the main types of paroxysmal dyskinesias and episodic ataxias, with recommendations for diagnosis and management of patients suffering from these conditions. Expert opinion: After secondary paroxysmal dyskinesias, the most common paroxysmal movement disorders are likely to be PRRT2-associated paroxysmal kinesigenic dyskinesias, which respond well to small doses of carbamazepine, and episodic ataxia type 2, which often responds to acetazolamide. Familial paroxysmal non-kinesigenic dyskinesias are largely caused by mutations in PNKD and have poor response to therapy but improve with age. Exercise-induced dyskinesias are genetically heterogeneous, caused by disorders of glucose transport, mitochondrial function, dopaminergic pathways or neurodegenerative conditions amongst others. GNAO1 and ADCY5 mutations can also cause paroxysmal movement disorders, often in the context of ongoing motor symptoms. Although a therapeutic trial is justified for classic cases and in limited resource settings, genetic testing may help direct initial or rescue therapy. Deep brain stimulation may be an option for severe cases.

Clinical, genetic, neurophysiological and functional study of new mutations in episodic ataxia type 1

BACKGROUND AND OBJECTIVE

Heterozygous mutations in KCNA1 cause episodic ataxia type 1 (EA1), an ion channel disorder characterised by brief paroxysms of cerebellar dysfunction and persistent neuromyotonia. This paper describes four previously unreported families with EA1, with the aim of understanding the phenotypic spectrum associated with different mutations.

METHODS

15 affected individuals from four families underwent clinical, genetic and neurophysiological evaluation. The functional impact of new mutations identified in the KCNA1 gene was investigated with in vitro electrophysiology and immunocytochemistry.

RESULTS

Detailed clinical documentation, dating back to 1928 in one family, indicates that all patients manifested episodic ataxia of varying severity. Four subjects from three families reported hearing impairment, which has not previously been reported in association with EA1. New mutations (R167M, C185W and I407M) were identified in three out of the four families. When expressed in human embryonic kidney cells, all three new mutations resulted in a loss of K(v)1.1 channel function. The fourth family harboured a previously reported A242P mutation, which has not been previously described in association with ataxia.

CONCLUSIONS

The genetic basis of EA1 in four families is established and this report presents the earliest documented case from 1928. All three new mutations caused a loss of K(v)1.1 channel function. The finding of deafness in four individuals raises the possibility of a link between K(v)1.1 dysfunction and hearing impairment. Our findings broaden the phenotypic range associated with mutations in KCNA1.

Clinical neurophysiology of the episodic ataxias: insights into ion channel dysfunction in vivo

Clinical neurophysiology has become an invaluable tool in the diagnosis of muscle channelopathies, but the situation is less clear cut with neuronal channelopathies. The genetic episodic ataxias are a group of disorders with heterogeneous phenotype and genotype, but share in common the feature of intermittent cerebellar dysfunction. Episodic ataxia (EA) types 1 and 2 are the most widely recognised of the autosomal dominant episodic ataxias and are caused by dysfunction of neuronal voltage-gated ion channels. There are central and peripheral nervous system manifestations in both conditions, and they are therefore good models of neuronal channelopathies to study neurophysiologically. To date most work has focussed upon characterising the electrophysiological properties of mutant channels in vitro. This review summarises the role of voltage-gated potassium and calcium channels, mutations of which underlie the main types of episodic ataxia types 1 and 2. The clinical, genetic and electrophysiological features of EA1 and EA2 are outlined, and a protocol for the assessment of these patients is proposed.

A novel KCNA1 mutation associated with global delay and persistent cerebellar dysfunction

Episodic Ataxia Type 1 is an autosomal dominant disorder characterized by episodes of ataxia and myokymia. It is associated with mutations in the KCNA1 voltage-gated potassium channel gene. In the present study, we describe a family with novel clinical features including persistent cerebellar dysfunction, cerebellar atrophy, and cognitive delay. All affected family members have myokymia and epilepsy, but only one individual has episodes of vertigo. Additional features include postural abnormalities, episodic stiffness and weakness. A novel KCNA1 mutation (c.1222G>T) which replaces a highly conserved valine with leucine at position 408 (p.Val408Leu) was identified in affected family members, and was found to augment the ability of the channel to inactivate. Together, our data suggests that KCNA1 mutations are associated with a broader clinical phenotype, which may include persistent cerebellar dysfunction and cognitive delay.

Novel mutation in KCNA1 causes episodic ataxia with paroxysmal dyspnea

Episodic ataxia type 1 (EA1) is an autosomal-dominant neurological disease caused by point mutations in the potassium channel-encoding gene KCNA1. It is characterized by attacks of ataxia and continuous myokymia. Respiratory muscle involvement has not been previously reported in EA1. We clinically evaluated a family with features of EA1 and paroxysmal shortness of breath. Coding and flanking intronic regions of KCNA1 were sequenced. We identified a novel 3-nucleotide deletion mutation in KCNA1 in the affected individuals. Our findings of a deletion mutation with unusual respiratory muscle involvement expand the genetic and clinical spectrum of EA1.

Episodic ataxia type 1: a neuronal potassium channelopathy

Episodic ataxia type 1 is a paroxysmal neurological disorder characterized by short-lived attacks of recurrent midline cerebellar dysfunction and continuous motor activity. Mutations in KCN1A, the gene encoding Kv1.1, a voltage-gated neuronal potassium channel, are associated with the disorder. Although rare, the syndrome highlights the fundamental features of genetic ion-channel diseases and serves as a useful model for understanding more common paroxysmal disorders, such as epilepsy and migraine. This review examines our current understanding of episodic ataxia type 1, focusing on its clinical and genetic features, pathophysiology, and treatment.

Expression in mammalian cells and electrophysiological characterization of two mutant Kv1.1 channels causing episodic ataxia type 1 (EA-1)

Episodic ataxia type 1 (EA-1) is a rare neurological disorder and was the first ionic channel disease to be associated with defects in a potassium channel. Until now 10 different point mutations in the KCNA1-gene have been reported to cause this disorder. We have investigated the functional consequences of two mutations leading to amino acid substitutions in the first and sixth transmembrane segments of a Kv1.1 channel subunit, by means of the patch-clamp technique; we injected cRNA coding for, respectively, F184C and V408A mutant Kv1.1 channels into mammalian cells and compared the resulting currents with those in the wild-type. The expression levels of F184C and V408A mutant channels relative to that of the wild-type was 38 and 68%, respectively. Since the single-channel conductance of the F184C mutant was similar to that of the wild-type (12 pS) without an apparent change in the maximum open probability, we conclude that the lower expression level in the F184C mutant channels is due to a reduced number of functional channels on the cell surface. F184C activated slower, and at more depolarized potentials, and deactivated faster compared with the wild-type. V408A channels deactivated and inactivated faster compared with the wild-type. Studies with different extracellular cations and tetraethylammonium gave no indication that the pore structure was changed in the mutant channels. Acetazolamide, that is helpful in some patients suffering from EA-1, was without effect on Kv1.1 wild-type or mutant channels. This study confirms and extends earlier studies on the functional consequences of Kv1.1 mutations associated with EA-1, in an attempt to understand the pathophysiology of the disease.

Episodic ataxia and myokymia syndrome: a new mutation of potassium channel gene Kv1.1

Episodic ataxia and myokymia syndrome is an autosomal dominant disorder characterized by persistent myokymia and attacks of unsteadiness, slurred speech, and tremulousness. This disease has been associated with point mutations in the potassium channel gene Kv1.1 (KCNA1), located at chromosome 12p13. Here, we describe a novel mutation within this gene in a newly diagnosed family.

Hereditary myokymia and paroxysmal ataxia linked to chromosome 12 is responsive to acetazolamide

A sixth family with autosomal dominantly inherited myokymia and paroxysmal ataxia is described. The syndrome in this family is linked to the recently discovered locus for inherited myokymia and paroxysmal ataxia on the human chromosome 12p, and a missense mutation is shown in the KCNA1 gene. The attacks of ataxia in this family compare well with those of previously described families and similarly are precipitated by kinesigenic stimuli, exertion, and startle. Responsiveness of these attacks to low dose acetazolamide is confirmed, but some loss of efficacy occurs with prolonged treatment, and side effects are notable. Although not all affected family members showed myokymia on clinical examination, electromyography invariably showed myokymic discharges, in one patient only after a short provocation with regional ischaemia. One affected family member also had attacks of paroxysmal kinesigenic choreoathetosis, responsive to carbamazepine.

AAEM minimonograph #44: diseases associated with excess motor unit activity

Stiff-man syndrome is due to hyperexcitability of anterior horn cells, possibly related to interference with the synthesis or action of gamma-aminobutyric acid. Unexpected acoustic and exteroceptive stimuli produce exaggerated muscle responses. Needle electrode examination of involved muscles yields nonspecific findings and demonstrates involuntary motor unit activity. The appearance and firing pattern of motor units are normal except that agonist and antagonist muscles may contract concurrently. Continuous muscle fiber activity (Isaacs' syndrome) comprises a heterogeneous group of hereditary and acquired disorders that cause hyperexcitability of peripheral nerves. Some are associated with electrophysiologic evidence of peripheral neuropathy and some are not. Repetitive afterdischarges often follow the M-, H-, and F-waves. Needle electrode examination reveals an abnormal pattern of motor unit firing, consisting of myokymic discharges, doublets and multiplets, neuromyotonic discharges, and fasciculations. These abnormalities may occur alone or in combination.

Episodic ataxia/myokymia syndrome is associated with point mutations in the human potassium channel gene, KCNA1

Episodic ataxia (EA) is a rare, familial disorder producing attacks of generalized ataxia, with normal or near-normal neurological function between attacks. One type of EA is characterized by brief episodes of ataxia with myokymia (rippling of muscles) evident between attacks. Linkage studies in four such families suggested localization of an EA/myokymia gene near the voltage gated K+ channel gene, KCNA1 (Kv1.1), on chromosome 12p. Mutation analysis of the KCNA1 coding region in these families identified four different missense point mutations present in the heterozygous state, indicating that EA/myokymia can result from mutations in this gene.

Syndrome of continuous muscle fiber activity. Case report with 11-year follow-up

A 16-year-old male patient who presented with muscle stiffness and dysphonia is described. Electromyography revealed continuous motor activity that was unaffected by peripheral nerve block or general anaesthesia, but was abolished by curare. The patient had a marked improvement after using phenytoin. The follow-up 11-years later corroborates with the proposed benignity of this syndrome, in spite of being dependent on medication.

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.

Familial dystonic choreoathetosis with myokymia; a sleep responsive disorder

A family is presented with paroxysmal dystonic choreoathetosis transmitted as a dominant trait over five generations. The family is unusual in the marked responsiveness of the episodes to short periods of sleep in several members, in the very variable age of onset, and in the association with prominent myokymia in some cases. These overlap features suggest a link between paroxysmal dystonic choreoathetosis and familial paroxysmal ataxia with myokymia.

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.

Autosomal dominant episodic ataxia: a heterogeneous syndrome

We describe six kindreds with autosomal dominant episodic ataxia, apparently representing three distinct syndromes. Four kindreds were characterized by episodic ataxia and response to acetazolamide, and in three, interictal nystagmus. One kindred was characterized by paroxysmal ataxia and in one member, paroxysmal choreoathetosis. The last kindred had brief attacks of ataxia and interictal neuromyotonia. The age of onset and severity of the disorder varied within each kindred. These kindreds illustrate the heterogeneity of episodic ataxia as well as the variable expressivity within each kindred.

The syndrome of continuous muscle fibre activity following gold therapy

A 72-year-old man suffering from arthritis received a total dose of 500 mg sodium aurothiomalate during a period of 5 months. His clinical state then deteriorated and he had to be hospitalized. Upon admission he was bedridden, his level of consciousness was slightly impaired, he was confused and respiration was laboured. Continuous muscle activity was noted on all extremities and at first, erroneously, fasciculations were diagnosed. The EMG exhibited continuous muscle fibre activity consisting of duplets, triplets and multiplets. The discharges occurred in an irregular pattern; when various muscles were examined at the same time no synchronicity could be observed between muscle discharges. In the left m. deltoideus an increased percentage of polyphasic potentials was found, whereas mean duration of motor unit potentials was normal. Spontaneous activity remained unchanged during sleep and administration of intravenous diazepam or phenytoin. Blocking of ulnar nerve at either elbow or wrist level did not stop spontaneous activity in m. abductor digiti quinti. Ischaemia increased the amount of discharges after 7 min. Within 4 months after termination of gold therapy the patient's condition improved and he was discharged from hospital. Regular EMG follow-up after 8 months showed complete cessation of abnormal spontaneous activities. Nerve conduction velocities were normal except for markedly reduced compound action potential in peroneal nerves. Continuous muscle fibre activity as a side-effect of gold therapy is described.

A dominantly inherited syndrome with continuous motor neuron discharges

A distinct syndrome with continuous motor neuron discharges apparently developed in seven members of a single family, involving both sexes and spanning three generations. Persistent vermiform twitching and episodic stiffness predominantly in lower extremity muscles occurred in early childhood and tended to be less severe in adulthood. In 2 patients the clinical manifestations improved with oral phenytoin and carbamazepine but not with parenteral diazepam. Insertional activity was normal, and continuous, rhythmical, normal-appearing muscle discharges were observed on electromyography. The cerebrospinal fluid levels of homovanillic acid and 5-hydroxyindoleacetic acid were increased in the proband. The disappearance of continuous muscle discharges during spinal anesthesia and the lack of response to diazepam indicated generation of the discharges from the proximal portion of the motor unit.