M.J. Zwarts

Experienced fatigue in facioscapulohumeral dystrophy, myotonic dystrophy, and HMSN-I

Objective: To assess the prevalence of severe fatigue and its relation to functional impairment in daily life in patients with relatively common types of neuromuscular disorders. Methods: 598 patients with a neuromuscular disease were studied (139 with facioscapulohumeral dystrophy, 322 with adult onset myotonic dystrophy, and 137 with hereditary motor and sensory neuropathy type I). Fatigue severity was assessed with Checklist Individual Strength (CIS-fatigue). Functional impairments in daily life were measured with the short form 36 item health questionnaire (SF-36). Results: The three different neuromuscular patient groups were of similar age and sex. Severe experienced fatigue was reported by 61–74% of the patients. Severely fatigued patients had more problems with physical functioning, social functioning, mental health, bodily pain, and general health perception. There were some differences between the three disorders in the effects of fatigue. Conclusions: Severe fatigue is reported by the majority of patients with relatively common types of neuromuscular disorders. Because experienced fatigue severity is associated with the severity of various functional impairments in daily life, it is a clinically and socially relevant problem in this group of patients.

A high-density multichannel surface electromyography system for the characterization of single motor units

An electromyography (EMG) system is presented that noninvasively records the electrical activity of a muscle with 126 densely spaced skin-surface electrodes. The electrodes are arranged in a two-dimensional array and integrated in a single container for ease of application. Signals are recorded “monopolarly”, with a reference electrode placed at a distance from the array. With this recording configuration, the surface EMG (sEMG) potential distribution can be described not only as a function of time, but also topographically. The availability of topographical information opens up a range of applications. Some of these have been described previously. However, the system presented is unique in that it allows exploration of all clinical and scientific possibilities of topographical sEMG. In its design, special attention was paid to user-friendliness and flexibility. With high-density multichannel sEMG, both the properties of a whole muscle and those of single motor units, the functional units of a muscle, can be studied. The latter belong to a realm that was long considered accessible only with needle-EMG, a conventional, invasive diagnostic technique. It is demonstrated that the additional topographical information can be used to characterize motor units in a way that is partially superior to needle EMG.

Transient cerebral white matter lesions in a patient with connexin 32 missense mutation

X-linked dominant Charcot-Marie-Tooth disease (CMT1X) is an inherited motor and sensory neuropathy that is associated with mutations in the gap junction protein connexin 32. Several authors have reported CNS involvement with1-2⇓ and without3-4⇓ cerebral abnormalities on MRI. We present a patient who developed subacute respiratory distress and a pseudobulbar syndrome after an episode of fever. MRI of the brain showed confluent cerebral white matter lesions. The clinical features and cerebral white matter lesions resolved spontaneously.nnA 14-year-old boy presented with gait difficulties and weakness in both feet. His symptoms had insidiously started 10 years previously. There was no history of recent immunization, and he did not use any drugs. Family history revealed that the patient’s mother from an early age had the same foot deformities as her son; …

Motor unit number estimation using high-density surface electromyography.

OBJECTIVEnTo present a motor unit number estimation (MUNE) technique that resolves alternation by means of high-density surface EMG.nnnMETHODSnHigh-density surface EMG, using 120 EMG channels simultaneously, is combined with elements of the increment counting technique (ICT) and the multiple-point stimulation technique. Alternation is a major drawback in the ICT. The spatial and temporal information provided by high-density surface EMG support identification and elimination of the effects of alternation. We determined the MUNE and its reproducibility in 14 healthy subjects, using a grid of 8 x 15 small electrodes on the thenar muscles.nnnRESULTSnMean MUNE was 271+/-103 (retest: 290+/-109), with a coefficient of variation of 22% and an intra-class correlation of 0.88. On average, 22 motor unit potentials (MUPs) were collected per subject. The representativity of this MUP sample was quantitatively assessed using the spatiotemporal information provided by high-density recordings.nnnCONCLUSIONSnMUNE values are relatively high, because we were able to detect many small MUPs. Reproducibility was similar to that of other MUNE techniques.nnnSIGNIFICANCEnOur technique allows collection of a large MUP sample non-invasively by resolving alternation to a large extent and provides insight into the representativity of this sample. The large sample size is expected to increase MUNE accuracy.

Psychiatric disorders appear equally in patients with myotonic dystrophy, facioscapulohumeral dystrophy, and hereditary motor and sensory neuropathy type I

Objectivesu2002–u2002 To study the presence of psychiatric comorbidity assessed by the use of a structured clinical interview and self‐reported questionnaires in a large sample of patients with adult‐onset myotonic dystrophy (DM), facioscapulohumeral muscular dystrophy (FSHD), and hereditary motor and sensory neuropathy type I (HMSN‐I), and to assess whether psychiatric comorbidity is related to fatigue severity and/or muscle strength.

The relation between daytime sleepiness, fatigue, and reduced motivation in patients with adult onset myotonic dystrophy

Daytime sleepiness, apathy, and lack of motivation are established clinical manifestations of myotonic dystrophy.1,2 A recent study showed that modafinil reduced daytime sleepiness and average sleep latency in a group of nine patients with myotonic dystrophy.3 This finding suggests that daytime sleepiness in patients with myotonic dystrophy and without obstructive sleep apnoea might be central in origin. A magnetic resonance imaging study indeed found evidence for a possible association between cerebral abnormalities in myotonic dystrophy and excessive daytime sleepiness.4 Although several studies have measured levels of fatigue with validated questionnaires in different neurological patient populations,5,6 fatigue questionnaires have not yet been related to the symptoms of daytime sleepiness in myotonic dystrophy. With the results of the modafinil study mentioned above in mind, our goal was to test the relations between excessive daytime sleepiness, experienced fatigue, and reduced motivation.nn### PatientsnnThe study was conducted at the outpatient clinic of the Neuromuscular Centre Nijmegen, based at the Institute of Neurology of the University Medical Centre Nijmegen in the Netherlands. Consecutive ambulant patients with a genetically confirmed diagnosis of (adult onset) myotonic dystrophy and an expanded CTG repeat on chromosome 19q13.3 (DM1) were invited to take part. Fatigue was not a criterion …

Mononeuropathy multiplex as the initial manifestation of neurofibromatosis type 2

The authors report a patient with neurofibromatosis type 2 (NF2) presenting with an axonal mononeuropathy multiplex. Sural nerve biopsy showed small scattered groups of Schwann cells transformed into irregular branching cells with abnormal cell—cell contacts. The authors hypothesize that defective Schwann cell function, due to inactivation of the NF2 gene product merlin, leads to changes in morphology, cell–cell contact, and growth, and finally to degeneration of axons.

Neuromuscular features in Marfan syndrome.

Marfan syndrome is a clinically and allelic heterogeneous, heritable connective tissue disorder with infrequently reported neuromuscular features. This study is the first to delineate these symptoms in a non‐selected population. Neuromuscular involvement was evaluated in 10 Marfan patients through a standardized questionnaire, physical examination, nerve conduction study (NCS), needle electromyography (EMG), muscle ultrasound, laboratory investigation, and muscle biopsy. Existing neuroimages were screened for dural ectasia and spinal meningeal cysts. Twenty healthy controls with similar age distribution completed the questionnaire.

Repeated ischaemic isometric exercise increases muscle fibre conduction velocity in humans: involvement of Na+‐K+‐ATPase

This study was performed to test two hypotheses: (1) ischaemic preconditioning (development of tolerance to ischaemia) influences muscle fibre conduction velocity (MFCV) during repeated ischaemic isometric exercise and (2) the increase in MFCV to supranormal levels during recovery from ischaemic exercise is caused by activation of Na+−K+‐ATPase. For this purpose, MFCV was measured with surface electromyography (sEMG) during repeated ischaemic isometric exercise of the brachioradial muscle (2 min at 30 % of maximal voluntary contraction). The involvement of ischaemic preconditioning was tested by changing the duration of ischaemia and by intra‐arterial infusion of adenosine (brachial artery, 50 μg min−1 dl−1). The role of Na+−K+‐ATPase was explored using ouabain (0.2 μg min−1 dl−1). During the exercise, MFCV decreased from 4.4 ± 0.2 m s−1 to 3.7 ± 0.2 m s−1 (P < 0.01, n= 13). Similar reductions in MFCV were observed during repeated exercise, irrespective of the reperfusion time (10 min vs. 18 min) or duration of the ischaemia (2 vs. 10 min). However, initial MFCV gradually increased for each subsequent contraction when contractions were repeated at 10 min intervals (4.4 ± 0.2 m s−1vs. 4.9 ± 0.2 m s−1 for the first and fourth contraction respectively; P < 0.01; n= 13). This increase was not observed when contractions were performed at 18 min intervals, nor when additional ischaemia was applied. Intra‐arterial adenosine did not affect MFCV. Intra‐arterial ouabain did not affect the reduction in MFCV during exercise but completely prevented the increase in MFCV during recovery: from 4.7 ± 0.2 m s−1 to 5.2 ± 0.2 m s−1vs. 4.5 ± 0.1 m s−1 to 4.5 ± 0.1 m s−1 in the absence and presence of ouabain respectively (P < 0.05 for ouabain effect; n= 6). In conclusion, ischaemic preconditioning is not involved in changes in MFCV during repeated ischaemic isometric exercise. The increase in MFCV during recovery from repeated ischaemic isometric exercise is caused by rapid activation of Na+−K+‐ATPase.

Loss of motor unit size and quadriceps strength over 10 years in post-polio syndrome

OBJECTIVEnTo investigate whether strength decline in post-polio syndrome (PPS) results from excessive distal axonal degeneration of enlarged motor units.nnnMETHODSnWe assessed changes over 10 years in isometric quadriceps strength, mean motor unit action potential (MUAP) size, root mean squared (RMS) amplitude, and level of interference (LOI) in 47 patients with PPS and 12 healthy controls, using high density surface EMG. At baseline, all patients had symptomatic quadriceps dysfunction, evidenced by transmission defects on single-fibre EMG.nnnRESULTSnMU size and strength declined significantly by 20% and 15%, respectively in patients with PPS. Those with the largest initial MU sizes exhibited the greatest losses of mean MU size (27%) and proportional decreases in quadriceps strength (23%). Initial strength, change in LOI and change in RMS amplitude together explained 35% of the variability in strength changes in patients. MU size of controls did not change, although they lost 29% strength.nnnCONCLUSIONSnMU size and strength declined concomitantly in a homogeneous cohort of patients with PPS and quadriceps dysfunction.nnnSIGNIFICANCEnThis long term follow-up study provides evidence that size diminution of enlarged MUs combined with a reduced number of active MUs contributes to the gradual strength decline in PPS.