Search

Patients with corticospinal tract dysfunction have slow voluntary movements with brisk stretch reflexes and spasticity. Previous studies reported reduced firing rates of motor units during voluntary contraction. To assess whether this firing behavior occurs because motor neurons do not respond normally to excitatory inputs, we studied motor units in patients with primary lateral sclerosis, a degenerative syndrome of progressive spasticity. Firing rates were measured from motor units in the wrist extensor muscles at varying levels of voluntary contraction ≤10% maximal force. At each force level, the firing rate was measured with and without added muscle vibration, a maneuver that repetitively activates muscle spindles. In motor units from age-matched control subjects, the firing rate increased with successively stronger contractions as well as with the addition of vibration at each force level. In patients with primary lateral sclerosis, motor-unit firing rates remained stable, or in some cases declined, with progressively stronger contractions or with muscle vibration. We conclude that excitatory inputs produce a blunted response in motor neurons in patients with primary lateral sclerosis compared with age-matched controls. The potential explanations include abnormal activation of voltage-activated channels that produce stable membrane plateaus at low voltages, abnormal recruitment of the motor pool, or tonic inhibition of motor neurons.

Myasthenia gravis (MG) is the most common autoimmune disease affecting neuromuscular junction transmission. MG is characterized by muscle weakness that worsens with activity and fluctuates over the course of the day. Involvement of respiratory musculature can lead to life-threatening crisis requiring intensive care unit care. Antibody testing is positive in most patients with MG. Treatment of MG includes short-term symptomatic treatment, chronic immunosuppression, surgical intervention, and immunomodulatory therapies for severe disease or crisis. We review advances in 5 areas relevant to diagnosis and management of MG: the role of IV immunoglobulin vs plasmapharesis in myasthenic crisis and severe disease; the clinical characterization of patients with antibodies to muscle-specific tyrosine kinase receptors; old and new investigational treatments; management of MG in pregnancy; and new confirmatory diagnostic tests.

Non-dystrophic myotonias are rare diseases caused by mutations in skeletal muscle chloride and sodium ion channels with considerable phenotypic overlap between diseases. Few prospective studies have evaluated the sensitivity of symptoms and signs of myotonia in a large cohort of patients. We performed a prospective observational study of 95 participants with definite or clinically suspected non-dystrophic myotonia recruited from six sites in the USA, UK and Canada between March 2006 and March 2009. We used the common infrastructure and data elements provided by the NIH-funded Rare Disease Clinical Research Network. Outcomes included a standardized symptom interview and physical exam; the Short Form-36 and the Individualized Neuromuscular Quality of Life instruments; electrophysiological short and prolonged exercise tests; manual muscle testing; and a modified get-up-and-go test. Thirty-two participants had chloride channel mutations, 34 had sodium channel mutations, nine had myotonic dystrophy type 2, one had myotonic dystrophy type 1, and 17 had no identified mutation. Phenotype comparisons were restricted to those with sodium channel mutations, chloride channel mutations, and myotonic dystrophy type 2. Muscle stiffness was the most prominent symptom overall, seen in 66.7% to 100% of participants. In comparison with chloride channel mutations, participants with sodium mutations had an earlier age of onset of stiffness (5 years versus 10 years), frequent eye closure myotonia (73.5% versus 25%), more impairment on the Individualized Neuromuscular Quality of Life summary score (20.0 versus 9.44), and paradoxical eye closure myotonia (50% versus 0%). Handgrip myotonia was seen in three-quarters of participants, with warm up of myotonia in 75% chloride channel mutations, but also 35.3% of sodium channel mutations. The short exercise test showed ≥10% decrement in the compound muscle action potential amplitude in 59.3% of chloride channel participants compared with 27.6% of sodium channel participants, which increased post-cooling to 57.6% in sodium channel mutations. In evaluation of patients with clinical and electrical myotonia, despite considerable phenotypic overlap, the presence of eye closure myotonia, paradoxical myotonia, and an increase in short exercise test sensitivity post-cooling suggest sodium channel mutations. Outcomes designed to measure stiffness or the electrophysiological correlates of stiffness may prove useful for future clinical trials, regardless of underlying mutation, and include patient-reported stiffness, bedside manoeuvres to evaluate myotonia, muscle specific quality of life instruments and short exercise testing.

Introduction: Non-dystrophic myotonia (NDM) is characterized by myotonia without muscle wasting. A standardized quantitative myotonia assessment (QMA) is important for clinical trials. Methods: Myotonia was assessed in 91 individuals enrolled in a natural history study using a commercially available computerized handgrip myometer and automated software. Average peak force and 90% to 5% relaxation times were compared with historical normal controls studied with identical methods. Results: Thirty subjects had chloride channel mutations, 31 had sodium channel mutations, 6 had DM2 mutations, and 24 had no identified mutation. Chloride channel mutations were associated with prolonged first handgrip relaxation times and warm-up on subsequent handgrips. Sodium channel mutations were associated with prolonged first handgrip relaxation times and paradoxical myotonia or warm-up, depending on underlying mutations. DM2 subjects had normal relaxation times but decreased peak force. Sample size estimates are provided for clinical trial planning. Conclusion: QMA is an automated, non-invasive technique for evaluating myotonia in NDM. Muscle Nerve 46: 482–489, 2012

Fellowships in experimental therapeutics are one solution to the challenge of developing the next generation of clinical researchers in the neurologic sciences. Through didactic teaching, mentoring, clinical research experience, hands-on training in trial design and execution, and preparation in

The spectrum of motor neuron diseases ranges from disorders that clinically are limited to lower motor neurons to those that exclusively affect upper motor neurons. Primary lateral sclerosis (PLS) is the designation for the syndrome of progressive upper motor neuron dysfunction when no other etiology is identified. Distinction between PLS and the more common amyotrophic lateral sclerosis (ALS) relies primarily on recognition of their symptoms and signs, as well as on ancillary, although non-specific, laboratory data. In this review, we survey the history of PLS from the initial descriptions to the present. We discuss the role of laboratory, electrodiagnostic, and imaging studies in excluding other diagnoses; the findings from major case series of PLS patients; and proposed diagnostic criteria. Consistent differences are evident in patients classified as PLS compared to those with ALS, indicating that, despite its limitations, this clinical designation retains important utility.

The M-current (IM), comprised of Kv7 channels, is a voltage-activated K+conductance that plays a key role in the control of cell excitability. In hippocampal principal cells,IMcontrols action potential (AP) accommodation and contributes to the medium-duration afterhyperpolarization, but the role ofIMin control of interneuron excitability remains unclear. Here, we investigatedIMin hippocampal stratum oriens (SO) interneurons, both from wild-type and transgenic mice in which green fluorescent protein (GFP) was expressed in somatostatin-containing interneurons. Somatodendritic expression of Kv7.2 or Kv7.3 subunits was colocalized in a subset of GFP+ SO interneurons, corresponding to oriens-lacunosum moleculare (O-LM) cells. Under voltage clamp (VC) conditions at −30 mV, the Kv7 channel antagonists linopirdine/XE-991 abolished theIMamplitude present during relaxation from −30 to −50 mV and reduced the holding current (Ihold). In addition, 0.5 mmtetraethylammonium reducedIM, suggesting thatIMwas composed of Kv7.2-containing channels. In contrast, the Kv7 channel opener retigabine increasedIMamplitude andIhold. When strongly depolarized in VC, the linopirdine-sensitive outward current activated rapidly and comprised up to 20% of the total current. In current-clamp recordings from GFP+ SO cells, linopirdine induced depolarization and increased AP frequency, whereas retigabine induced hyperpolarization and arrested firing. In multicompartment O-LM interneuron models that incorporatedIM, somatodendritic placement of Kv7 channels best reproduced experimentally measuredIM. The models suggest that Kv3- and Kv7-mediated channels both rapidly activate during single APs; however, Kv3 channels control rapid repolarization of the AP, whereas Kv7 channels primarily control the interspike interval.

Context Nondystrophic myotonias (NDMs) are rare diseases caused by mutations in skeletal muscle ion channels. Patients experience delayed muscle relaxation causing functionally limiting stiffness and pain. Mexiletine-induced sodium channel blockade reduced myotonia in small studies; however, as is common in rare diseases, larger studies of safety and efficacy have not previously been considered feasible. Objective To determine the effects of mexiletine for symptoms and signs of myotonia in patients with NDMs. Design, Setting, and Participants A randomized, double-blind, placebo-controlled 2-period crossover study at 7 neuromuscular referral centers in 4 countries of 59 patients with NDMs conducted between December 23, 2008, and March 30, 2011, as part of the National Institutes of Health–funded Rare Disease Clinical Research Network. Intervention Oral 200-mg mexiletine or placebo capsules 3 times daily for 4 weeks, followed by the opposite intervention for 4 weeks, with 1-week washout in between. Main Outcome Measures Patient-reported severity score of stiffness recorded on an interactive voice response (IVR) diary (scale of 1 = minimal to 9 = worst ever experienced). Secondary end points included IVR-reported changes in pain, weakness, and tiredness; clinical myotonia assessment; quantitative measure of handgrip myotonia; and Individualized Neuromuscular Quality of Life summary quality of life score (INQOL–QOL, percentage of maximal detrimental impact). Results Mexiletine significantly improved patient-reported severity score stiffness on the IVR diary. Because of a statistically significant interaction between treatment and period for this outcome, primary end point is presented by period (period 1 means were 2.53 for mexiletine and 4.21 for placebo; difference, −1.68; 95% CI, −2.66 to −0.706; P Conclusion In this preliminary study of patients with NDMs, the use of mexiletine compared with placebo resulted in improved patient-reported stiffness over 4 weeks of treatment, despite some concern about the maintenance of blinding. Trial Registration clinicaltrials.gov Identifier: NCT00832000

Objective: To evaluate test-retest reliability of vHOT in DM1. Background Delayed release of the handgrip is a common symptom in DM1, reflecting myotonia plus a variable contribution of finger extensor weakness. Previous methods to quantify myotonia required sophisticated equipment and labor-intensive analysis. Video recording coupled with blinded review is an accepted procedure to evaluate motor performance in clinical trials. Design/Methods: vHOT recordings were made using a standardized procedure in 20 individuals with DM1. Subjects were asked to perform maximal handgrip for 5 seconds, followed by rapid extension of fingers without shaking of the hand. Each participant completed 3 trials with a 10-minute rest between trials. vHOT was recorded on 2 consecutive days by the same evaluator. vHOT recordings were later reviewed using the standard video editing software by 2 blinded raters. Time for maximal hand opening was measured separately for the thumb and long finger. Results: The mean vHOT was 4.6 ± 5.6 seconds. vHOT was longer for the thumb than the long finger. The correlation of vHOT between trials on the same day (r = 0.94-0.97) was better than for trials on the separate days (r = 0.88). There is no evidence for “warm-up” in successive trials. The ICC for test-retest concordance for the same rater on 2 successive days was 0.71. The ICC for concordance between 2 raters was 0.96. Conclusions: vHOT provides a simple low-cost method to assess grip myotonia and finger extension. The inter-rater reliability is excellent and the test-retest reliability is moderate, reflecting the physiologic variability of myotonia over time. vHOT may provide a suitable endpoint for studies of disease progression and therapeutic response in DM1. Supported by: NIH U54NS48843. Disclosure: Dr. Puwanant has nothing to disclose. Dr. Statland has nothing to disclose. Dr. Dilek has nothing to disclose. Dr. Moxley has nothing to disclose. Dr. Thornton has received personal compensation for activities with Genzyme Corporation as a consultant. Dr. Thornton has received research support from Isis Pharmaceuticals, Inc.

Objective: To describe genotype-phenotype correlations in non-dystrophic myotonia (NDM). Background NDM are heterogeneous disorders caused by mutations in skeletal muscle sodium (SCN4A) and chloride channel (CLCN1) genes. Although NDMs are distinct, it is at times difficult to distinguish them clinically. Design/Methods: 95 participants with NDM were recruited from 6 centers across the United States, England, and Canada. Mutational and clinical analyses were performed in 93. They were categorized into chloride channel (CLCN1), sodium channel (SCN4A), myotonic dystrophy type 2 (DM2), and unknown mutations. We included DM2 since they clinically present as NDM. We quantitated symptoms and myotonia measurements. Results: Of the 93 subjects reviewed, 29 had CLCN1, 31 SCN4A, and 7 DM2 mutations with 26 as yet unknown. Stiffness was the most prominent symptom in all subtypes and occurred earlier in the SCN (median-5 yrs) vs CLCN (10 yrs) and DM2 (35 yrs) (p=0.0001). Painful myotonia was reported in SCN (25/31), CLCN (16/29), and DM2 (5/7) (p=0.19). Episodic weakness was reported in all subtypes: 23/31 SCN, 12/29 CLCN, and 4/7 DM2. Frequency of fixed weakness was higher in DM2 (6/7) compared to SCN (7/30) and CLCN (9/29) (p=0.012). Muscle hypertrophy was most common in CLCN (21/29) followed by SCN (13/31). DM2 patients did not have hypertrophy. Eye closure myotonia was observed more in SCN (23/31) compared to CLCN (7/29) or DM2 (2/7) (p=0.0005). Grip myotonia warm-up was noted in 20/29 CLCN, 8/31 SCN, and 1/7 DM2 subjects. Paradoxical hand grip & eye closure myotonia was seen in 16/31 SCN. Conclusions: While clinical features can help differentiate various NDM subtypes, mutational analysis is required due to an overlap in the clinical findings in NDM patients. Supported by: NIH/Office of Rare Disease Research Network sponsored Consortium for Clinical Investigations of Neurological Channelopathies (CINCH). Disclosure: Dr. Trivedi has nothing to disclose. Dr. Bundy has nothing to disclose. Dr. Raja Rayan has nothing to disclose. Dr. Salajegheh has nothing to disclose. Dr. Statland has nothing to disclose. Dr. Venance has received personal compensation for activities with Genzyme Corporation. Dr. Wang has nothing to disclose. Dr. Fialho has nothing to disclose. Dr. Hart has nothing to disclose. Dr. Gorham has nothing to disclose. Dr. Herbelin has nothing to disclose. Dr. Amato has received personal compensation for activities with MedImmune, Amgen, and Biogen Idec as a medical advisory board member. Dr. Hanna has nothing to disclose. Dr. Griggs has nothing to disclose. Dr. Barohn has received personal compensation for activities with Talecris Biotherapeutics, Genzyme Corporation and Speakers Bureau. Dr. Barohn has received research support from Alexion Pharmaceuticals.

Objective: To determine identifiable subgroups of patients with primary lateral sclerosis (PLS) with distinct clinical features as a first step in identifying patients likely to have the same disorder. Methods: Twenty-five patients meeting previously proposed diagnostic criteria for PLS were seen for examination, measurement of gait and finger tapping speed, and physiologic tests to assess motor pathways. Motor cortex excitability and central motor conduction time were assessed with transcranial magnetic stimulation. Brainstem motor pathways were assessed by the acoustic startle reflex. MRS was performed in a subgroup of patients to assess metabolites in the motor cortex. Results: Fifty-six percent of the patients with PLS had a similar pattern of symptom progression, which the authors termed ascending. In these patients spasticity began in the legs and progressed slowly and steadily. Spasticity in the arms developed 3.6 years after the legs, on average, and speech impairment followed 1.5 years later. Motor evoked potentials were absent. MRS showed a mean reduction of N-acetylaspartate/creatinine in the motor cortex. The remaining patients with PLS had heterogeneous patterns of symptom progression and physiology. Conclusions: Patients with PLS with an ascending progression of symptoms form a distinct clinical subgroup that may be amenable to investigations of etiology and treatment.