The mechanism of benign paroxysmal positional nystagmus

A characteristic nystagmus profile of benign paroxysmal positional nystagmus (BPPN) was determined from analyses of horizontal and vertical electro-oculographic recordings in 8 patients. The vertical component was upbeat in both eyes (fast phase toward the ground in the head-hanging position) while the horizontal component was dissociated with the ipsilateral eye beating away from the down ear and the contralateral eye beating toward the down ear. The amplitude of the vertical component was larger in the contralateral eye while that of the horizontal component was larger in the ipsilateral eye. This dissociated nystagmus profile is consistent with a burst of excitatory activity originating in the posterior canal of the ear that is undermost at the end of the positioning maneuver.

Association of benign recurrent vertigo and migraine in 208 patients

The aim of this study was to determine the association of benign recurrent vertigo (BRV) and migraine, using standardized questionnaire-based interview of 208 patients with BRV recruited through a University Neurotology clinic. Of 208 patients with BRV, 180 (87%) met the International Classification of Headache Disorders 2004 criteria for migraine: 112 migraine with aura (62%) and 68 without aura (38%). Twenty-eight (13%) did not meet criteria for migraine. Among patients with migraine, 70% experienced headache, one or more auras, photophobia, or auditory symptoms with some or all of their vertigo attacks, meeting the criteria for definite migrainous vertigo. Thirty per cent never experienced migraine symptoms concurrent with vertigo attacks. These met criteria for probable migrainous vertigo. Among patients without migraine, 21% experienced either photophobia or auditory symptoms with some or all of their vertigo attacks; 79% experienced only isolated vertigo. The age of onset and duration of vertigo attacks did not differ significantly between patients with (34 +/- 1.2 years) and patients without migraine (31 +/- 3.0 years). In patients with migraine, the age of onset of migraine headache preceded the onset of vertigo attacks by an average of 14 years and aura preceded vertigo by 8 years. The most frequent duration of vertigo attacks was between 1 h and 1 day. Benign recurrent vertigo is highly associated with migraine, but a high proportion of patients with BRV and migraine never have migraine symptoms during their vertigo attacks. Other features such as age of onset and duration of vertigo are similar between patients with or without migraine.

Otolith dysfunction in vestibular neuritis: recovery pattern and a predictor of symptom recovery

OBJECTIVES

To prospectively follow patients with vestibular neuritis (VN), to compare the recovery pattern of canal and otolith dysfunction, and to determine which tests best predict symptom recovery.

METHODS

Between March 2006 and December 2006, 51 consecutive patients with unilateral VN were enrolled within 7 days of onset (average 3 days). Otolith function tests included ocular torsion (OT), subjective visual vertical (SVV), and vestibular evoked myogenic potential (VEMP), and canal function tests included head-shaking nystagmus (HSN), caloric stimulation, and head-thrust testing. Patients returned for two follow-up evaluations at approximately 1 week and 6 weeks after the initial evaluation.

RESULTS

On the first examination, all patients had abnormal HSN, caloric, and head-thrust test results, and at least one otolith-related test abnormality: abnormal tilt of SVV (48/51, 94%), abnormal OT (42/51, 82%), or abnormal VEMPs (25/51, 49%). The degree of SVV tilts correlated with the degree of OT for one or both eyes (p < 0.05). Skew deviation was observed in 7 patients (14%), and a complete ocular tilt reaction was detected in only 2 patients. On follow-up, otolith test results returned to normal more rapidly than canal test results. The head-thrust test was the best predictor of symptom recovery. Eighty percent of patients who continued to report dizziness at the last follow-up visit had a positive head-thrust test result, whereas only 10% of patients who were not dizzy had a positive head-thrust test result.

CONCLUSION

Otolith-related test abnormalities improve more rapidly than canal-related test abnormalities after vestibular neuritis. If patients have a positive head-thrust test result on follow-up, they are more likely to be dizzy.

The relevance of migraine in patients with Meńière's disease

CONCLUSION

Coexistent migraine affects relevant clinical features of patients with Ménière's disease (MD).

OBJECTIVE

Epidemiological studies have shown an association between migraine and MD. We sought to determine whether the coexistence of migraine affects any clinical features in patients with MD.

PATIENTS AND METHODS

In this retrospective case-control study of University Neurotology Clinic patients, 50 patients meeting 1995 AAO-HNS criteria for definite MD were compared to 18 patients meeting the same criteria in addition to the 2004 IHS criteria for migraine (MMD). All had typical low frequency sensorineural hearing loss and episodes of rotational vertigo. Outcome measures included: sex, age of onset of episodic vertigo or fluctuating hearing loss, laterality of hearing loss, aural symptoms, caloric responses, severity of hearing loss, and family history of migraine, episodic vertigo or hearing loss.

RESULTS

Age of onset of episodic vertigo or fluctuating hearing loss was significantly lower in patients with MMD (mean +/- 1.96*SE = 37.2 +/- 6.3 years) than in those with MD (mean +/- 1.96*SE = 49.3 +/- 4.4 years). Concurrent bilateral aural symptoms and hearing loss were seen in 56% of MMD and 4% of MD patients. A family history of episodic vertigo was seen in 39% of MMD and 2% of MD patients.

Episodic vertical oscillopsia with progressive gait ataxia: clinical description of a new episodic syndrome and evidence of linkage to chromosome 13q

We describe four families with late onset episodic vertical oscillopsia and progressive gait ataxia. Probands presented between the ages of 40 and 64 years with initial symptoms of episodic vertical oscillopsia and interictal downbeat nystagmus. A mild gait ataxia developed over several years. Triggers included physical exertion, alcohol and caffeine. Patients did not respond to acetazolamide. Genetic screening for episodic ataxia types 1 and 2, and spinocerebellar ataxias 1, 2, 3 and 6 were negative. Using ancestral identity by descent analysis and dense single nucleotide polymorphism (SNP) genotyping throughout the genome, an interval of 28.6 cM (approximately 14.2 Mb) on chromosome 13q12.11-q13.3, composed of 1259 SNPs, was shared between affected individuals in two of the four families and highlighted a region of suggestive linkage (LOD >2.7).

Primary episodic ataxias: diagnosis, pathogenesis and treatment

Primary episodic ataxias are autosomal dominant channelopathies that manifest as attacks of imbalance and incoordination. Mutations in two genes, KCNA1 and CACNA1A, cause the best characterized and account for the majority of identified cases of episodic ataxia. We summarize current knowledge of clinical and genetic diagnosis, genotype-phenotype correlations, pathophysiology and treatment of episodic ataxia syndromes. We focus on unresolved issues including phenotypic and genetic heterogeneity, lessons from animal models and technological advancement, rationale and feasibility of various treatment strategies, and shared mechanisms underlying episodic ataxia and other far more prevalent paroxysmal conditions such as epilepsy and migraine.

Prolonged hemiplegic episodes in children due to mutations in ATP1A2

BACKGROUND

Familial hemiplegic migraine (FHM) is an unusual migraine syndrome characterised by recurrent transient attacks of unilateral weakness or paralysis as part of the migraine aura. Genetically and clinically heterogeneous, FHM1 is caused by mutations in CACNA1A and FHM2 by mutations in ATP1A2.

AIM

Three children with prolonged hemiplegia were tested for mutations in CACNA1A or ATP1A2.

METHODS

Mutations in CACNA1A and ATP1A2 were screened for by denaturing high performance liquid chromatography and confirmed by sequencing. Expression studies were performed to characterise the functional consequences of these mutations.

RESULTS

No mutation was found in the FHM1 gene while three mutations were identified in the FHM2 gene. All three mutations were missense: two were novel and one was de novo; none was found in controls. Functional studies in HeLa cells showed complete loss of mutant pump function without interfering with the wild-type pump, consistent with haploinsufficiency.

CONCLUSION

We identified novel disease causing mutations in the FHM2 gene. Genetic screening for FHM should be considered in a child with prolonged hemiplegia even if there is no prior history or family history of migraine or hemiplegic episodes.

Genetic heterogeneity of autosomal dominant nonprogressive congenital ataxia

We studied a family with nonprogressive congenital ataxia (NPCA) previously reported in 1985. Follow-up evaluation documented a nonprogressive course. Older family members developed ataxic spells and vertical oscillopsia triggered by stress and exercise. Linkage analysis using a 10K single-nucleotide polymorphism array found suggestive linkage to four loci on chromosomes 1q44, 5q35.1-35.3, 7q36.2-36.3, and 9q31.2-32 and ruled out linkage to the NPCA locus on 3p, proving genetic heterogeneity for autosomal dominant NPCA.

Cerebellar infarction presenting isolated vertigo: Frequency and vascular topographical patterns

OBJECTIVE

To determine the frequency of cerebellar infarction mimicking vestibular neuritis (VN), the pattern of clinical presentation, and the territory of the cerebellar infarction when it simulates VN.

METHODS

We studied 240 consecutive cases of isolated cerebellar infarction in the territories of the cerebellar arteries diagnosed by brain MRI from the acute stroke registry at the Keimyung University Dongsan Medical Center.

RESULTS

We identified 25 patients (10.4%) with isolated cerebellar infarction who had clinical features suggesting VN. Two types of cerebellar infarction simulating VN were found: isolated spontaneous prolonged vertigo with imbalance as a sole manifestation of cerebellar infarction (n = 24) and isolated spontaneous prolonged vertigo with imbalance as an initial manifestation of cerebellar infarction (n = 1) followed by delayed neurologic deficits 2 days after the onset. The cerebellar infarction territory most commonly involved was the medial branch of the posterior inferior cerebellar artery territory (24/25: 96%), followed by the anterior inferior cerebellar artery territory (1/25: 4%). None of patients with infarcts in the territory of the superior cerebellar artery or multiple cerebellar arteries showed isolated spontaneous prolonged vertigo.

CONCLUSIONS

Cerebellar infarction simulating vestibular neuritis is more common than previously thought. Early recognition of the pseudo-vestibular neuritis of vascular cause may allow specific management.

Relative atrophy of the flocculus and ocular motor dysfunction in SCA2 and SCA6

Two hereditary ataxia syndromes show distinct profiles of region-specific atrophy and ocular motor deficits. Selective pontine atrophy is associated with slowed saccades in ataxin-2 mutations, and selective floccular atrophy is associated with impaired pursuit and gaze-holding abnormalities in Ca(V)2.1 mutations. Although the flocculus seems to be spared relative to the pons in ataxin-2 mutations, and pursuit and gaze-holding appear to be relatively normal, these can be difficult to assess at the bedside, as corrective saccades are also slow and hard to discern. Here, we show the presence of significant floccular atrophy compared with controls in both ataxin-2 and Ca(V)2.1 mutations, which raises the possibility that abnormalities of smooth pursuit or gaze-holding are present in both conditions.

Diffusion tensor MRI shows abnormal brainstem crossing fibers associated with ROBO3 mutations

Horizontal gaze palsy with progressive scoliosis (HGPPS) is caused by mutations in the ROBO3 gene, critical for the crossing of long ascending medial lemniscal and descending corticospinal tracts in the medulla. Diffusion tensor imaging in a patient with HGGPS revealed the absence of major pontine crossing fiber tracts and no decussation of the superior cerebellar peduncles. Mutations in the ROBO3 gene lead to a widespread lack of crossing fibers throughout the brainstem.

Pontine and cerebellar atrophy correlate with clinical disability in SCA2

Spinocerebellar ataxia type 2 (SCA2) has protean manifestations, and a clinical marker of progression is needed. Although MRI is a promising tool, it is unclear whether the degree of atrophy shown on MRI is correlated with clinical dysfunction. Here the authors used high-resolution volumetric MRI analysis to show that cerebellar and pontine volumes specifically and closely correlate with functional staging scores.

Neurologic features of horizontal gaze palsy and progressive scoliosis with mutations in ROBO3

OBJECTIVE

To review the neurologic, neuroradiologic, and electrophysiologic features of autosomal recessive horizontal gaze palsy and progressive scoliosis (HGPPS), a syndrome caused by mutation of the ROBO3 gene on chromosome 11 and associated with defective decussation of certain brainstem neuronal systems.

METHODS

The authors examined 11 individuals with HGPPS from five genotyped families with HGPPS. Eight individuals had brain MRI, and six had electrophysiologic studies.

RESULTS

Horizontal gaze palsy was fully penetrant, present at birth, and total or almost total in all affected individuals. Convergence, ocular alignment, congenital nystagmus, and vertical smooth pursuit defects were variable between individuals. All patients developed progressive scoliosis during early childhood. All appropriately studied patients had hypoplasia of the pons and cerebellar peduncles with both anterior and posterior midline clefts of the pons and medulla and electrophysiologic evidence of ipsilateral corticospinal and dorsal column-medial lemniscus tract innervation. Heterozygotes were unaffected.

CONCLUSIONS

The major clinical characteristics of horizontal gaze palsy and progressive scoliosis were congenital horizontal gaze palsy and progressive scoliosis with some variability in both ocular motility and degree of scoliosis. The syndrome also includes a distinctive brainstem malformation and defective crossing of some brainstem neuronal pathways.

CACNA1A mutations causing episodic and progressive ataxia alter channel trafficking and kinetics

BACKGROUND

CACNA1A encodes CaV2.1, the pore-forming subunit of P/Q-type voltage-gated calcium channel complexes. Mutations in CACNA1A cause a wide range of neurologic disturbances variably associated with cerebellar degeneration. Functional studies to date focus on electrophysiologic defects that do not adequately explain the phenotypic findings.

OBJECTIVE

To investigate whether some missense mutations might interfere with protein folding and trafficking, eventually leading to protein aggregation and neuronal injury.

METHODS

The authors studied the functional consequences of two pore missense mutations, C287Y and G293R, in two families with EA2, one newly discovered and the other previously reported. Both mutations caused episodic and interictal ataxia. The biophysical properties of mutant and wild type calcium channels were examined by whole-cell patch-clamp recordings in transfected COS-7 cells. The plasma membrane targeting was visualized by confocal fluorescence imaging on CaV2.1 tagged with green fluorescent protein.

RESULTS

The mutant channels exhibited a marked reduction in current expression and deficiencies in plasma membrane targeting.

CONCLUSIONS

In addition to altered channel function, the deficiency in protein misfolding and trafficking associated with the C287Y and G293R mutants may contribute to the slowly progressive cerebellar ataxia.

Mutation in the glutamate transporter EAAT1 causes episodic ataxia, hemiplegia, and seizures

BACKGROUND

Transporters, ion pumps, and ion channels are membrane proteins that regulate selective permeability and maintain ionic gradients across cell membranes. Mutations in CACNA1A encoding a neuronal calcium channel and ATP1A2 encoding an ion pump cause episodic ataxia, hemiplegic migraine, and seizures. Mutant gene products of both CACNA1A and ATP1A2 may affect neurotransmission of glutamate, the most abundant excitatory amino acid neurotransmitter.

METHODS

We examined our patient population with episodic ataxia and hemiplegic migraine but with no mutation in either CACNA1A or ATP1A2. We looked for mutations in SLC1A3, which encodes the glutamate transporter excitatory amino acid transporter (EAAT) 1 that is important in removing glutamate from the synaptic cleft.

RESULTS

A patient with episodic ataxia, seizures, migraine, and alternating hemiplegia has a heterozygous mutation in SLC1A3 that is not present in his asymptomatic parents and controls. Expression studies of the mutant EAAT1 showed decreased expression of the protein with a markedly reduced capacity for glutamate uptake. When coexpressed, the mutant EAAT1 decreased the activity of wild-type EAAT1 but not of two other transporters EAAT2 or EAAT3, suggesting that mutant EAAT1 specifically multimerizes with wild-type EAAT1 to exert its dominant negative effect.

CONCLUSION

Our data show that a heterozygous mutation in EAAT1 can lead to decreased glutamate uptake, which can contribute to neuronal hyperexcitability to cause seizures, hemiplegia, and episodic ataxia.

Suggestive linkage to chromosome 6q in families with bilateral vestibulopathy

BACKGROUND

Of the more than 40 genetically defined dominantly inherited hearing loss syndromes, only a few are associated with bilateral vestibulopathy. No genetic mutations have been identified in families with bilateral vestibulopathy and normal hearing.

OBJECTIVE

To perform a genome-wide scan for linkage in four families with dominantly inherited bilateral vestibulopathy.

METHODS

Patients in four families reported brief episodes of vertigo followed by imbalance and oscillopsia. Bilateral vestibulopathy was documented with quantitative rotational testing. Most patients with bilateral vestibulopathy also had migraine. A 10 cM genome-wide screen was conducted using 423 microsatellite markers to identify linkage with vestibulopathy.

RESULTS

The authors identified a 24 cM region on chromosome 6q suggestive of linkage to vestibulopathy in these four families (maximum lod score of 2.9 at marker D6S1556). A small fifth family with a different phenotype was not linked to this region on chromosome 6q.

CONCLUSIONS

This is the first report of linkage in families with dominantly inherited vestibulopathy and normal hearing. Genetic heterogeneity is likely with inherited vestibulopathy.

Temporal bone histopathology in dominantly inherited audiovestibular syndrome

OBJECTIVE

To describe the clinical and pathologic features of a new dominantly inherited audiovestibular syndrome.

METHODS

History, examination, and audiometric testing in the proband, brother, and son; quantitative rotational testing in the proband and son; histopathology of the cochlea and vestibular labyrinth in the proband; sequencing candidate genes COCH and MYO7A in the brother and son.

RESULTS

Affected family members developed slowly progressive hearing loss beginning in their late 30s and progressive imbalance in their early 70s. Three of four affected had brief (minutes) episodes of vertigo typically occurring a few times per year. Auditory and vestibular function testing documented a slowly progressive loss of auditory and vestibular function. Postmortem examination showed a loss of hair cells in the cochlea and vestibular receptor organs. There were no cellular infiltrates or acidophilic deposits. No mutations were found in the COCH or MYO7A genes.

CONCLUSIONS

This dominantly inherited audiovestibular syndrome results in a selective loss of hair cells in the auditory and vestibular end organs. Finding the causative gene could have important implications for understanding the pathophysiology of presbycusis and dysequilibrium of aging.

Episodic ataxia type 1 with distal weakness: a novel manifestation of a potassium channelopathy

Episodic ataxia type1 (EA1) is an autosomal dominant disorder characterised by episodes of ataxia, dysarthria, tremor and visual disturbances lasting for seconds or minutes, precipitated by physical and emotional stress, startle or sudden movements. In addition there is continuous myokymia. Phenotypic variants such as the combination with epilepsy, shortening of the Achilles tendon in children, transient postural abnormalities in infancy, and a very few patients with longer lasting episodes have been reported. We describe a 10-year-old girl with EA1 who has distal weakness with paresis of the extensors of the feet and prolonged spells of limb stiffness (neuromyotonia) lasting up to 12 hours. A novel single nucleotide change at position 785 T > C that alters a highly conserved residue in the third transmembrane segment of the voltage-gated potassium channel Kv1.1 was found.

Clinical spectrum of episodic ataxia type 2

The authors searched for mutations in CACNA1A in patients with episodic ataxia and describe the clinical spectrum in genetically defined patients. Eighteen families and nine sporadic cases of episodic ataxia were evaluated for mutations in CACNA1A. The families were first genotyped to check for linkage to the chromosome 19p locus of CACNA1A. In families consistent with linkage and in the sporadic cases, the authors screened for polymorphisms in CACNA1A using single-strand conformational polymorphism and denaturing high performance liquid chromatography followed by direct sequencing to identify specific nucleotide changes. Of the 18 families, 11 were linked to 19p and mutations were found in 9. Mutations were detected in four of the nine sporadic cases. Overall, five nonsense mutations, four missense mutations, two deletions, one insertion, and one donor splice mutation were identified. All but two of the 64 genetically defined patients reported episodes of ataxia (two members of one family only had progressive ataxia). All but one had onset before age 20 and all but four had interictal nystagmus. Migraine headaches occurred in more than half, and about two thirds reported a good response to treatment with acetazolamide. Vertigo and weakness accompanied the ataxia in more than half of the genetically defined patients. One family had multiple members with epilepsy. A wide range of mutations in CACNA1A were associated with episodic ataxia. Four of 13 were missense mutations; the remainder predicted truncated proteins. The mutations were scattered throughout the gene, and only 2 of the 13 mutations identified in our laboratory have been reported by other laboratories, so it will not be possible to screen a few "hot spots" in CACNA1A. Overall, the type of mutation, missense versus nonsense, or the location of altered or truncated amino acid residues did not predict the clinical phenotype.

Presynaptic failure of neuromuscular transmission and synaptic remodeling in EA2

OBJECTIVE

To further investigate the basis of abnormal neuromuscular transmission in two patients with congenital myasthenic syndrome associated with episodic ataxia type 2 (EA2) using stimulated single fiber EMG (SFEMG) and in vitro microelectrode studies.

METHODS

Two patients with genetically characterized EA2 previously shown to have abnormal neuromuscular transmission by voluntary SFEMG were studied with stimulated SFEMG and anconeus muscle biopsy with microelectrode studies and electron microscopy of the neuromuscular junction.

RESULTS

In vivo stimulated SFEMG showed signs of presynaptic failure, with jitter and blocking that improved with increased stimulation frequency. Additional evidence of presynaptic failure was provided by the in vitro microelectrode studies, which showed marked reduction of the end plate potential quantal content in both patients. Of note, the end plate potentials showed high sensitivity to N-type blockade with omega-conotoxin not seen in controls. The ultrastructural studies revealed some evidence of small nerve terminals apposed to normal or mildly overdeveloped postsynaptic membranes, suggesting an ongoing degenerative process.

CONCLUSIONS

The authors demonstrated presynaptic failure of neurotransmission in patients with heterozygous nonsense mutations in CACNA1A. The contribution of non-P-type calcium channels to the process of neurotransmitter release in these patients likely represents a compensatory mechanism, which is insufficient to restore normal neuromuscular transmission.

Age-related change of the neuronal number in the human medial vestibular nucleus: a stereological investigation

An unbiased stereological method was used to assess the effect of aging on the number of neurons in the human medial vestibular nucleus. We studied 13 normal brainstem specimens (age at death from 40 to 93 years) that were part of a prior study that counted neuronal profiles and used a correction factor to estimate the number of neurons in the human vestibular nucleus. On average, we found 151.10(3) (CV = 0.15) neurons in the medial vestibular nucleus, which is 18% more than that in the prior study. Regression analysis showed a significant decrease in the number of neurons with aging. This age-related neuronal loss in the vestibular nucleus could have important functional implications regarding the well-known deterioration in balance that occurs with aging.

Nodulus infarction mimicking acute peripheral vestibulopathy

The authors report two patients with cerebellar infarctions in the territory of the medial branch of the posterior inferior cerebellar artery who had vertigo, spontaneous ipsilesional nystagmus, and contralesional truncal lateropulsion. Although one of the two patients had slight dysmetria, overall signs closely mimicked those of acute peripheral vestibulopathy. The authors suggest that interruption of nodulouvular inhibitory projections to vestibular nuclei may account for the vestibular signs.

Sudden bilateral simultaneous deafness with vertigo as a sole manifestation of vertebrobasilar insufficiency

A 68 year old woman presented with bilateral sudden simultaneous hearing loss and transient spontaneous vertigo as a sole manifestation of vertebrobasilar insufficiency. Extensive investigation to exclude other causes was unremarkable. Magnetic resonance imaging of the brain, including diffusion images, showed no abnormalities. A magnetic resonance angiogram showed severe stenosis of the middle third of the basilar artery. A pure tone audiogram showed moderate sensorineural-type hearing loss bilaterally. The localisation and mechanism of an isolated cochleovestibular dysfunction are discussed.

Familial horizontal gaze palsy with progressive scoliosis maps to chromosome 11q23-25

Horizontal gaze palsy with progressive scoliosis (HGPS) is a rare, autosomal recessive disorder characterized by a congenital absence of conjugate horizontal eye movement, with progressive scoliosis developing in childhood or adolescence. The authors identified two unrelated consanguineous families with HGPS. Genomewide homozygosity mapping and linkage analysis mapped the disease locus to a 30-cM interval on chromosome 11q23-25 (combined maximum multipoint lod score Z = 5.46).

Otolith function in cerebellar ataxia due to mutations in the calcium channel gene CACNA1A

The vestibulo-ocular reflexes stabilize retinal images during head movements. While there is a wealth of information about the interaction between the cerebellum and vestibulo-ocular reflexes mediated by the semicircular canals, little is known about the role of the cerebellum in the generation of the otolith-mediated linear vestibulo-ocular reflex (LVOR). By means of transient linear acceleration of the whole body along the interaural axis, we examined the LVOR in six patients with hereditary cerebellar ataxia due to mutations of the calcium channel gene CACNA1A, five with spinocerebellar ataxia type 6 (SCA6) and one with episodic ataxia type 2 (EA-2). Six age-matched normal subjects served as controls. Using a peak acceleration of 0.5 g in combination with recording by the binocular scleral magnetic search coil method, it was possible to study the latency and sensitivity of the LVOR in the first 150 ms after motion onset. The normal LVOR showed a significant dependence on viewing distance and covaried with vergence angle, and could be enhanced by the presence of a visible target. In contrast, the LVOR of ataxic patients had normal latency but significantly decreased sensitivity that was not enhanced with visible or nearer targets despite normal vergence. Substituting for the normal smooth LVOR slow phase, ataxic patients employed catch-up saccades 150-250 ms after motion onset. These findings suggest a critical role of the cerebellum in the modulation of otolith-ocular signals that is independent of motor vergence.

Loss-of-function EA2 mutations are associated with impaired neuromuscular transmission

OBJECTIVE

To examine the functional consequences of episodic ataxia type 2 (EA2)-causing nonsense and missense mutations in vitro and to characterize the basis of fluctuating weakness in patients with E2A.

BACKGROUND

Mutations in CACNA1A encoding the Ca(v)2.1 calcium channel subunit cause EA2 through incompletely understood mechanisms. Although the Ca(v)2.1 subunit is important for neurotransmission at the neuromuscular junction, weakness has not been considered a feature of EA2.

METHODS

The disease-causing mutations in three unrelated patients with EA2 and fluctuating weakness were identified by mutation screening and sequencing. Mutant constructs harboring mutations R1281X, F1406C, R1549X were transfected into COS7 cells and expressed for patch clamp studies. Single-fiber electromyography (SFEMG) was performed in patients to examine synaptic transmission at the neuromuscular junction.

RESULTS

Functional studies in COS7 cells of nonsense and missense EA2 mutants demonstrated markedly decreased current densities compared with wild type. SFEMG demonstrated jitter and blocking in these patients with EA2, compared with normal subjects and three patients with SCA-6.

CONCLUSION

EA2-causing missense and nonsense mutations in CACNA1A produced mutant channels with diminished whole cell calcium channel activity in vitro due to loss of function. Altered biophysical properties or reduced efficiency of plasma membrane targeting of mutant channels may contribute to abnormal neuromuscular transmission, manifesting as myasthenic syndrome.

Vertigo and the enlarged vestibular aqueduct syndrome

An enlarged vestibular aqueduct (EVA) is one of the most commonly identified inner ear bony malformations in children with sensorineural hearing loss of unknown cause. Most previous reports have focused on hearing loss, but individuals with EVA may also experience paroxysmal vertigo lasting minutes to hours. We report the clinical vestibular features and vestibular function testing of two children and one adult with EVA who had a history of sensorineural hearing loss and presented to our Neurotology Clinic for the evaluation of episodic vertigo. All the patients had an antecedent history of profound bilateral sensorineural hearing loss that had been present since early childhood. The onset of vertigo was delayed into adulthood in one patient. Episodes of vertigo could be triggered by minor head trauma or vigorous physical activity. Despite recurrent episodes of vertigo, vestibular function was normal or moderately impaired compared with the severe auditory deficit. Careful analysis of temporal bone CT demonstrated EVA. Associated enlargement of the membranous endolymphatic sac was evident on brain MRI. While hearing loss is a prominent symptom in patients with EVA, vestibular symptoms may cause referral to a neurologist. Although hearing loss occurs early in childhood, vestibular symptoms can be delayed into adulthood, a finding not previously reported.

Age-related changes in vestibular function: a longitudinal study

The objective of this study was to identify age-related changes in the vestibulo-ocular reflex (VOR) in normal older subjects and patients complaining of disequilibrium followed serially over time. Cross-sectional studies have found decreases in vestibular function in older subjects compared to younger subjects, but no prior longitudinal studies have been made following the same older subjects over time. We measured VOR responses using step and sinusoidal stimuli in 110 normal subjects and 51 patients with disequilibrium of unknown cause. This report focuses on 57 normal subjects who were able to return for five yearly examinations and 7 patients who were found to have severe bilateral vestibulopathy on the initial examination. In the normal subjects, there was a significant shortening of the VOR time constant to step changes in angular velocity and an amplitude-dependent decrease in gain and increase in phase lead of low-frequency sinusoidal responses over the five examinations. There was also a decrease in the gain of visual-vestibular responses at low frequencies of sinusoidal stimulation over the five examinations. The patients with bilateral vestibulopathy showed relatively little change in vestibular function over the five years of follow-up. This is the first longitudinal study to show age-related decreases in vestibular responses in normal older subjects. The VOR changes identified were not associated with symptoms or signs of disequilibrium. A small subgroup of patients with disequilibrium of unknown cause had profound bilateral vestibulopathy that remained stable during follow-up. These patients likely had an underlying disease even though in most cases the disease process could not be identified.

Brain volume changes on longitudinal magnetic resonance imaging in normal older people

BACKGROUND AND PURPOSE

The purpose of this study is to investigate the longitudinal age-related changes in human brain volume using stereological methods.

METHODS

Sixty-six older participants (34 men, 32 women, age [mean +/- SD] 78.9 +/- 3.3 years, range 74-87 years) with normal baseline and follow-up examinations underwent 2 MRIs (magnetic resonance imaging) of the brain on average 4.4 years apart. The volumes of the cerebrum (defined as cortex, basal ganglia, thalamus, and white matter), lateral ventricles, and cerebellum were estimated on the 2 MRIs using an unbiased stereological method (Cavalieri principle).

RESULTS

The annual decrease (mean +/- SD) of the cerebral volume was 2.1% +/- 1.6% (P < .001). The average volume of the lateral ventricles on the second MRI was increased by 5.6% +/- 3.6% per year (P < .001). The average volume of the cerebellum on the second MRI was decreased by 1.2% +/- 2.2% per year (P < .001). Even though the average cerebral volume was significantly different between men and women on initial MRI and second MRI, the percentage change of the age-related cerebral volume decrease in male and female brains between initial MRI and second MRI were identical.

CONCLUSIONS

The findings showed that there was age-related atrophy of cerebrum and cerebellum and age-related disproportional enlargement of lateral ventricles in normal older men and women.

Drop attacks in older patients secondary to an otologic cause

The clinical features and treatment of seven patients with drop attacks attributable to inner ear disease presenting after age 65 are described. A neurologic or cardiovascular cause of drop attacks was initially suspected. Audiovestibular testing documented a unilateral inner ear disorder. The salient clinical features of these cases are discussed. The patients underwent ablative vestibular surgery, and all compensated well and were free of vertigo and falls up to 10 years postoperatively.

A prospective study of cerebral white matter abnormalities in older people with gait dysfunction

OBJECTIVES

The authors previously reported cross-sectional data suggesting a relationship between cerebral white matter hyperintensities (WMH) and gait and balance dysfunction in older people. There have been no longitudinal MRI studies to address this issue. The current study compared progression of WMH in subjects with gait and balance dysfunction with that in healthy subjects.

METHODS

Two brain MRI were performed on 70 healthy, ambulatory subjects (mean baseline age 79, range 74 to 88) with no identifiable neurologic disease. The mean time between MRI was 4 years. Gait and balance were quantified using the Tinetti Balance and Mobility Scale, and falls were documented each year. On T2-weighted MRI, total hyperintense volume (HV) within three periventricular levels was estimated using the Cavalieri principle, and WMH were graded (0 to 4) using an established semiquantitative scale.

RESULTS

Compared with those with normal gait and balance, subjects whose Tinetti scores dropped markedly (> 4 points) between first and second MRI showed a significantly greater mean increase in HV during follow-up. The larger group of subjects with an abnormal Tinetti score (< 24) at the time of second MRI showed a significantly greater mean increase in HV, compared with those with normal gait and balance at follow-up. Subjects with marked WMH at baseline showed significantly greater increase in HV over time. Subjects with abnormal Tinetti scores had significantly more falls than subjects with normal Tinetti scores.

CONCLUSIONS

Some older people develop gait and balance dysfunction that is associated with gradual onset of cerebral white matter disease.

Vestibular function in severe bilateral vestibulopathy

OBJECTIVES

To assess residual vestibular function in patients with severe bilateral vestibulopathy comparing low frequency sinusoidal rotation with the novel technique of random, high acceleration rotation of the whole body.

METHODS

Eye movements were recorded by electro-oculography in darkness during passive, whole body sinusoidal yaw rotations at frequencies between 0.05 and 1.6 Hz in four patients who had absent caloric vestibular responses. These were compared with recordings using magnetic search coils during the first 100 ms after onset of whole body yaw rotation at peak accelerations of 2800 degrees /s(2). Off centre rotations added novel information about otolithic function.

RESULTS

Sinusoidal yaw rotations at 0.05 Hz, peak velocity 240 degrees/s yielded minimal responses, with gain (eye velocity/head velocity)<0.02, but gain increased and phase decreased at frequencies between 0.2 and 1.6 Hz in a manner resembling the vestibulo-ocular reflex. By contrast, the patients had profoundly attenuated responses to both centred and eccentric high acceleration transients, representing virtually absent responses to this powerful vestibular stimulus.

CONCLUSION

The analysis of the early ocular response to random, high acceleration rotation of the whole body disclosed a profound deficit of semicircular canal and otolith function in patients for whom higher frequency sinusoidal testing was only modestly abnormal. This suggests that the high frequency responses during sinusoidal rotation were of extravestibular origin. Contributions from the somatosensory or central predictor mechanisms, might account for the generation of these responses. Random, transient rotation is better suited than steady state rotation for quantifying vestibular function in vestibulopathic patients.

Prosper Ménière and his disease

In 1861, Prosper Ménière presented a paper before the French Academy of Medicine in which he described a series of patients with episodic vertigo and hearing loss. He also mentioned the postmortem examination of a young girl who experienced vertigo after a hemorrhage into the inner ear. Prior to that time, vertigo was thought to be a cerebral symptom similar to epileptic seizures. Ménière pointed out that vertigo frequently had a benign course and that common treatments, such as bleeding, often did more harm than good. He was not attempting to define a disease or syndrome but rather to emphasize that vertigo could originate from damage to the inner ear. Confusion regarding the clinical and pathologic features of Ménière disease persisted well into the 20th century.

Slowing of voluntary and involuntary saccades: an early sign in spinocerebellar ataxia type 7

We describe quantitative oculomotor findings in a patient with subclinical spinocerebellar ataxia type 7 (SCA7) and a borderline mutation of 38 CAG repeats and her daughter with SCA7 and 46 repeats. Both subjects demonstrated significant slowing of voluntary and involuntary saccades, but retinal examination was normal. Smooth pursuit and fixation suppression of VOR were mildly impaired. Slow saccades may be the earliest neurologic finding even in asymptomatic SCA7 patients with normal ocular fundi. The SCA7 mutation probably has an early impact on brainstem fast eye movement centers.

Familial benign recurrent vertigo

Benign recurrent vertigo (BRV) has been previously linked to migraine but there have been no prior studies of families with BRV. We studied the families of 24 patients who presented to our clinic with BRV and who reported a family history of similar attacks of vertigo. All probands underwent diagnostic evaluation to exclude identifiable causes of recurrent vertigo and they completed a standardized medical questionnaire pertaining to episodic vertigo and the features of migraine. This questionnaire was also sent to all relatives of the probands who agreed to participate. Of 220 relatives who returned questionnaires, 37% reported BRV and 50% met the diagnostic criteria for migraine. By contrast, only one of 43 (2%) unrelated spouses reported BRV and 10 of 43 (23%) met the diagnostic criteria for migraine. More than two-thirds of relatives with BRV met the diagnostic criteria for migraine and the majority reported that they had a typical migraine headache with at least some of their episodes of vertigo. Both BRV and migraine showed a female preponderance (more than 2 to 1). Familial BRV seems to be a migraine syndrome, probably inherited in an autosomal dominant fashion with decreased penetrance in men. In the search for the causative gene, vertigo may be a more useful marker than migraine because recurrent vertigo is relatively rare in the general population whereas migraine is very common.

Impairments in the initial horizontal vestibulo-ocular reflex of older humans

To determine age-related changes, the initial horizontal vestibulo-ocular reflex (VOR) of 11 younger normal subjects (aged 20-32 years) was compared with that of 12 older subjects (aged 58-69 years) in response to random transients of whole-body acceleration of 1,000 and 2,800 degrees/s2 delivered around eccentric vertical axes ranging from 10 cm anterior to 20 cm posterior to the eyes. Eye and head positions were sampled at 1,200 Hz using magnetic search coils. Subjects fixed targets 500 cm or 15 cm distant immediately before the unpredictable onset of rotation in darkness. For all testing conditions, younger subjects exhibited compensatory VOR slow phases with early gain (eye velocity/head velocity, interval 35-45 ms from onset of rotation) of 0.90 +/- 0.02 (mean +/- SEM) for the higher head acceleration, and 0.79 +/- 0.02 for the lower acceleration. Older subjects had significantly (P < 0.0001) lower early gain of 0.77 +/- 0.04 for the higher head acceleration and 0.70 +/- 0.02 for the lower acceleration. Late gain (125-135 ms from onset of rotation) was similar for the higher and lower head accelerations in younger subjects. Older subjects had significantly lower late gain at the higher head acceleration, but gain similar to the younger subjects at the lower acceleration. All younger subjects maintained slow-phase VOR eye velocity to values > or = 200 degrees/s throughout the 250-ms rotation, but, after an average of 120 ms rotation (mean eccentricity 13 degrees), 8 older subjects consistently had abrupt declines (ADs) in slow-phase VOR velocity to 0 degree/s or even the anticompensatory direction. These ADs were failures of the VOR slow phase rather than saccades and were more frequent with the near target at the higher acceleration. Slow-phase latencies were 14.4 +/- 0.4 ms and 16.8 +/- 0.4 ms for older subjects at the higher and lower accelerations, significantly longer than comparable latencies of 10.0 +/- 0.5 ms and 12.0 +/- 0.6 ms for younger subjects. Late VOR gain modulation with target distance was significantly attenuated in older subjects only for the higher head acceleration.