RESPIRATION IN DYSTROPHIA MYOTONICA

Respiratory dysfunction in myotonic dystrophy type 1: A systematic review

Myotonic dystrophy type 1 (DM1) is one of the most common muscular dystrophies in adults. This review summarises the current literature regarding the natural history of respiratory dysfunction in DM1, the role of central respiratory drive and peripheral respiratory muscle involvement and its significance in respiratory function, and investigates the relationship between genetics (CTG repeat length) and respiratory dysfunction. The review included all articles that reported spirometry on 10 or more myotonic dystrophy patients. The final review included 55 articles between 1964 and 2017. The major conclusions of this review were (1) confirmation of the current consensus that respiratory dysfunction, predominantly a restrictive ventilatory pattern, is common in myotonic dystrophy and is associated with alveolar hypoventilation, chronic hypercapnia, and sleep disturbance in the form of sleep apnoea and sleep related disordered breathing; (2) contrary to commonly held belief, there is no consensus in the literature regarding the relationship between CTG repeat length and severity of respiratory dysfunction and a relationship has not been established; (3) the natural history and time-course of respiratory functional decline is very poorly understood in the current literature; (4) there is a consensus that there is a significant involvement of central respiratory drive in this alveolar hypoventilation however the current literature does not identify the mechanism for this.

Noninvasive assessment of respiratory muscle strength and activity in Myotonic dystrophy

OBJECTIVE

To evaluate sensitivity/specificity of the maximum relaxation rate (MRR) of inspiratory muscles, amplitude of electromyographic activity of the sternocleidomastoid (SCM), scalene (SCA), parasternal (2ndIS) and rectus abdominis (RA) muscles; lung function and respiratory muscle strength in subjects with Myotonic dystrophy type 1 (DM1) compared with healthy subjects.

DESIGN AND METHODS

Quasi-experimental observational study with control group. MRR of inspiratory muscles, lung function and amplitude of the electromyographic activity of SCM, SCA, 2ndIS and RA muscles during maximum inspiratory pressure (PImax), maximum expiratory pressure (PEmax) and sniff nasal inspiratory pressure (SNIP) tests were assessed in eighteen DM1 subjects and eleven healthy.

RESULTS

MRR was lower in DM1 group compared to healthy (P = 0.001) and was considered sensitive and specific to identify disease in DM1 and discard it in controls, as well as SNIP% (P = 0.0026), PImax% (P = 0.0077) and PEmax% (P = 0.0002). Contraction time of SCM and SCA was higher in DM1 compared to controls, respectively, during PImax (P = 0.023 and P = 0.017) and SNIP (P = 0.015 and P = .0004). The DM1 group showed lower PImax (P = .0006), PEmax (P = 0.0002), SNIP (P = 0.0014), and higher electromyographic activity of the SCM (P = 0.002) and SCA (P = 0.004) at rest; of 2ndIS (P = 0.003) during PEmax and of SCM (P = 0.02) and SCA (P = 0.03) during SNIP test.

CONCLUSIONS

MD1 subjects presented restrictive pattern, reduced respiratory muscle strength, muscular electrical activity and MRR when compared to higher compared to controls. In addition, the lower MRR found in MD1 subjects showed to be reliable to sensitivity and specificity in identifying the delayed relaxation of respiratory muscles.

Emergency Caesarean Section in a Patient with Myotonic Dystrophy: A Case of Failed Postoperative Extubation in a Patient with Mild Disease

A 21-year-old primiparous patient with subclinical myotonic dystrophy presented at a tertiary hospital at 38 weeks gestation in active labour, having previously been reviewed in the high-risk pregnancy clinic. A non-reassuring cardiotocogram and raised foetal scalp lactate necessitated an emergency caesarean section. On extubation following an otherwise unremarkable general anaesthetic, the patient required prompt re-intubation due to respiratory compromise, followed by a more gradual period of weaning from positive pressure ventilation. This review explores the implications of myotonic dystrophy for anaesthesia, discusses its multi-system involvement and highlights the difficulties in identifying at-risk patients in the perioperative setting.

Modafinil for the treatment of hypersomnia associated with myotonic muscular dystrophy in adults: a multicenter, prospective, randomized, double-blind, placebo-controlled, 4-week trial

BACKGROUND

Myotonic muscular dystrophy type 1 (MMD1) is the most common form of adult MD, with a mean prevalence of 1 in 8000. Excessive daytime sleepiness (ie, hypersomnia) is a common complication of MMD1.

OBJECTIVE

The aim of this study was to evaluate the efficacy and tolerability of modafinil for the treatment of hypersomnia in adults with MMD1.

METHODS

This multicenter, prospective, randomized, double-blind, placebo-controlled study consisted of a prerandomization period (90 to 2 days before randomization) and a 4-week randomization period in which patients were assigned to receive either active treatment (modafinil 300 mg/d) or placebo. The study was conducted at 3 clinics in France between February 2000 and June 2002. Adult patients aged > or =18 years, with genetically proven MMD1, an Epworth Sleepiness Scale (ESS) score >10, and a mean latency to sleep onset < or =8 minutes measured by the Multiple Sleep Latency Test (MSLT) were eligible. The primary efficacy end point was the Maintenance of Wakefulness Test (MWT) score at 4 weeks. Secondary end points included the mean MSLT score and scores from the ESS, physician's assessment of the therapeutic effect and the patient's global self-assessment via visual analog scale, the 17-item Hamilton Depression Rating Scale, and the Short Form Health Survey (SF-36) quality-of-life assessment.

RESULTS

A total of 28 patients (15 men, 13 women; mean [SD] age, 40 [12.7] years [range, 18-69 years]; 100% white; modafinil group, 13; placebo group, 15) completed the study without protocol violations. Of the 28 patients with MMD1 included in the analysis, 21 had adult-onset MMD1. At 4 weeks, the mean MWT score was 16.4 (3.3) minutes in the modafinil group and 15.8 (3.8) minutes in the placebo group (P = NS). At the end of the randomization period, there were no significant between-group differences in any secondary outcome. A total of 8 patients (4 in each group) reported > or =1 adverse event, including digestive, neurologic, and skin symptoms. Weight loss was reported in 1 patient (2 kg).

CONCLUSION

In this small study conducted in an adult population with MMD1 and a high prevalence of hyper-somnia, modafinil had no significant effects on daytime somnolence measured using objective MWTs.

Psychostimulants for hypersomnia (excessive daytime sleepiness) in myotonic dystrophy

BACKGROUND

Excessive daytime sleepiness is a common symptom of myotonic dystrophy. Psychostimulants are drugs increasingly used to treat hypersomnia in myotonic dystrophy.

OBJECTIVES

To search systematically for, and combine all evidence from, randomised trials relating to the effects of psychostimulants in myotonic dystrophy patients with hypersomnia.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Trials Register (January 2006), MEDLINE (from January 1966 to January 2006) and EMBASE (from January 1980 to January 2006) for randomised trials concerning psychostimulants in myotonic dystrophy, checked the bibliographies of identified papers and made enquiries of the authors of the papers. The search for relevant studies was updated in January 2006.

SELECTION CRITERIA

We considered all randomised or quasi randomised trials that have evaluated any type of psychostimulants (versus a placebo or no treatment) in children or adults with proven myotonic dystrophy and hypersomnia.

DATA COLLECTION AND ANALYSIS

Potentially relevant papers were scrutinised by two authors and the selection of eligible studies was agreed by them and a third author. Data were extracted by one author and checked by a second author.

MAIN RESULTS

Primary outcome. One trial using a modified maintenance of wakefulness test showed an improvement by 5.70 (95% confidence intervals 0.1 to 11.3) minutes more in the modafinil than the control group. Secondary outcomes. In a double-blind crossover study of 10 participants with myotonic dystrophy, there was no difference between the selegiline and placebo periods in mean improvement in the multiple sleep latency test. Two trials, involving 60 participants in total, evaluated the efficacy and safety of modafinil in adults with myotonic dystrophy-related daytime sleepiness. The weighted mean difference on the Epworth Sleepiness Scale was -1.59 (95% confidence intervals, -2.77 to -0.42) in favour of modafinil.

AUTHORS' CONCLUSIONS

There is no evidence to support the routine use of psychostimulants to treat hypersomnia in myotonic dystrophy. There is some evidence from two studies that modafinil may improve daytime sleepiness. More randomised trials are needed to evaluate the efficacy and safety of psychostimulants.

Psychostimulants for hypersomnia (excessive daytime sleepiness) in myotonic dystrophy

BACKGROUND

Excessive daytime sleepiness is a common symptom of myotonic dystrophy. Psychostimulants are drugs increasingly used to treat hypersomnia in myotonic dystrophy.

OBJECTIVES

To search systematically for, and combine all evidence from, randomised trials relating to the effects of psychostimulants in myotonic dystrophy patients with hypersomnia.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Trial Register (searched May 2001) for randomised trials concerning psychostimulants in myotonic dystrophy, we searched of the bibliographies of identified papers and we contacted the authors of the papers.

SELECTION CRITERIA

We considered all randomised or quasi randomised trials that have evaluated any type of psychostimulants (versus a placebo or no treatment) in children or adults with proven myotonic dystrophy and hypersomnia.

DATA COLLECTION AND ANALYSIS

Potentially relevant papers were scrutinised by two reviewers and the selection of eligible studies was agreed by them and a third reviewer. Data were extracted by one reviewer and checked by a second reviewer.

MAIN RESULTS

Primary outcome We found no trial that assessed the effect of a psychostimulant on the results of the maintenance of wakefulness tests. Secondary outcomes Only one eligible trial was found. In this crossover double blind study of 10 patients with myotonic dystrophy, the efficacy of selegiline was evaluated against a placebo on the multiple sleep latency test. There was no difference between the selegiline and placebo periods in mean improvement in the multiple sleep latency test scale.

REVIEWER'S CONCLUSIONS

There is no evidence to support the use of a psychostimulant to treat hypersomnia in myotonic dystrophy. Randomised trials are needed to evaluate the efficacy and safety of psychostimulants.

Electrophysiological evaluation of oropharyngeal swallowing in myotonic dystrophy

OBJECTIVE

Oropharyngeal dysphagia is a common feature of patients with myotonic dystrophy and is not usually perceived due to their emotional deficits and lack of interest. The aim was to show the existence and frequency of subclinical electrophysiological abnormalities in oropharyngeal swallowing and to clarify the mechanisms of dysphagia in myotonic dystrophy.

METHODS

Eighteen patients with myotonic dystrophy were examined for oropharyngeal phase of swallowing by clinical and electrophysiological methods. Ten patients had dysphagia whereas 11 patients had signs and symptoms reflecting CNS involvement. Four patients with myotonia congenita and 30 healthy volunteers served as controls. Laryngeal movements were detected by means of a piezoelectric sensor. EMG activities of the submental muscle (SM-EMG) and needle EMG of the cricopharyngeal muscle of the upper eosophageal sphincter (CP-EMG) were also recorded during swallowing.

RESULTS

In about 70% of the patients with myotonic dystrophy, the existence of oropharyngeal dysphagia was indicated objectively by means of the technique of "dysphagia limit" and by clinical evaluation. Duration of the swallowing reflex as defined by the laryngeal relocation time (0-2 time interval) and submental muscle excitation as a part of the swallowing reflex (A-C interval) were significantly prolonged in patients with myotonic dystrophy, especially in dysphagic patients. Triggering time of the swallowing reflex (A-0 interval) also showed significant prolongation, especially in the patients having both dysphagia and CNS involvement. During swallowing, CP muscle activity was abnormal in 40% of the patients with myotonic dystrophy.

CONCLUSION

Both myopathic weakness and myotonia encountered in oropharyngeal muscles play an important part in the oral and the pharyngeal phases of swallowing dysfunction in myotonic dystrophy. It was also suggested that CNS involvement might contribute to the delay of the triggering of the swallowing reflex and some abnormal EMG findings in the CP sphincter, resulting in oropharyngeal dysphagia in myotonic dystrophy.

Postural breathing pattern changes in patients with myotonic dystrophy

We recorded by pneumotachography the breathing in nine patients with myotonic dystrophy (MD), both seated and supine and with eyes open in both positions. Irregular breathing (coefficient of variation >20% for VT and TTOT) was observed in six of the patients, two of whom showed irregularity in both positions whilst the remaining four had irregular breathing only when supine. In addition, in this latter group, irregularities first appeared in VT and only after a few minutes in TTOT. Whereas in the group exhibiting irregular breathing in both seated and supine positions, irregularities were observed throughout the recording. However, no significant difference in any ventilatory variable was observed as between the two postures. Rib cage (RC) and abdomen (AB) motions were recorded by uncalibrated respiratory inductance plethysmography. Although for MD patients the mean values of the RC/AB ratio lay within the normal range the relative decrease in value as between seated (0.78+/-0.52) and supine (0.31+/-0.13) position was less than in healthy subjects. These observations suggest that MD may cause deficiencies in several mechanisms. Analyses of the respiratory pattern in each patient may provide information leading to the identification of the impaired respiratory mechanisms.

Control of breathing in patients with limb girdle dystrophy: a controlled study

BACKGROUND

In patients with limb girdle dystrophy the relative contribution of peripheral factors (respiratory muscle weakness, and lung and/or airway involvement) and central factors (blunted and/or inadequate chemoresponsiveness) in respiratory insufficiency has not yet been established. To resolve this, lung volumes, arterial blood gas tensions, respiratory muscle strength, breathing pattern and neural respiratory drive were investigated in a group of 15 patients with limb girdle dystrophy. An age-matched normal group was studied as a control.

METHODS

Respiratory muscle strength was assessed as an arithmetic mean of maximal inspiratory (MIP) and expiratory (MEP) pressures. Breathing pattern was evaluated in terms of volume (ventilation VE, tidal volume VT) and time (respiratory frequency Rf, inspiratory time TI, expiratory time TE) components of the respiratory cycle. Neural respiratory drive was assessed as the mean inspiratory flow (VT/TI), mouth occlusion pressure (P0.1) and electromyographic activity (EMG) of the diaphragm (EMGd) and the intercostal parasternal (EMGp) muscles. In 10 of the 15 patients the responses to carbon dioxide (PCO2) stimulation were also evaluated.

RESULTS

Most patients exhibited a moderate decrease in vital capacity (VC) (range 37-87% of predicted), MIP (range 23-84% of predicted), and/or MEP (range 13-41% of predicted). The arterial carbon dioxide tension (PaCO2) was increased in three patients breathing room air, while PaO2 was normal in all. Compared with the control group Rf was higher, and VT, TI and TE were lower in the patients. EMGd and EMGp were higher whilst VT/TI and P0.1 were normal in the patients. Respiratory muscle strength was inversely related to EMGd and EMGp. PaCO2 was found to relate primarily to VC and duration of illness, but not to respiratory muscle strength. During hypercapnic rebreathing delta VE/delta PCO2, delta VT/delta PCO2, and delta P0.1/delta PCO2 were lower than normal, whilst delta EMGd/delta PCO2 and delta EMGp/delta PCO2 were normal in most patients. A direct relation between respiratory muscle strength and delta VT/delta PCO2 was found.

CONCLUSIONS

The respiratory muscles, especially expiratory ones, are weak in patients with limb girdle dystrophy. Reductions in respiratory muscle strength are associated with increased neural drive and decreased ventilatory output (delta VT/delta PCO2). The decrease in VC, together with the duration of disease, influence PaCO2. VC is a more useful test than respiratory muscle strength for following the course of limb girdle dystrophy.

Myotonic dystrophy with alveolar hypoventilation and hypersomnia: a clinicopathological study

We present a case of myotonic dystrophy accompanied by alveolar hypoventilation and hypersomnia. Case history, pulmonary function tests, polygraphic recording, and multiple sleep latency test, concomitant with a restrictive ventilatory abnormality, suggested a central origin of alveolar hypoventilation and hypersomnia in our case. The most significant neuropathological findings were in the tegmentum of the brain stem. Severe neuronal loss and gliosis were observed in the midbrain and pontine raphe, particularly in dorsal raphe nucleus and superior central nucleus. Pontine and medullary reticular formation also showed a marked cell loss and fibrillary gliosis. The alveolar hypoventilation and the hypersomnia in our case may be attributed to these morphological abnormalities, and would appear to be central in nature.

Respiratory effort perception at rest and during carbon dioxide rebreathing in patients with dystrophia myotonica

BACKGROUND

Breathlessness appears to be closely related to the perception of the outgoing motor command to breathe and should be increased in the presence of muscle weakness. However, breathlessness is not a common symptom in patients with chronic muscle disease who have weak respiratory muscles. The factors that determine the perception of respiratory effort in such patients have not been examined.

METHODS

The inspiratory effort sensation during resting breathing and progressive hypercapnia was investigated in 12 patients with dystrophia myotonica with weak respiratory muscles (nine men and three women of mean (SD) age 41.1 (10.5) years; maximum inspiratory pressure 43.1 (17.2) cm H2O) and an age and sex matched control group of normal subjects of mean age 39.6 (10.6) years and a maximum inspiratory pressure of 123 (15.2) cm H2O.

RESULTS

During resting breathing with a mouthpiece no differences were seen in inspiratory effort sensation, mouth occlusion pressure, or tidal volume, but inspiratory time and cycle duration were significantly shorter in the patients with dystrophia. Minute ventilation (VE) was significantly higher in the patients (15.8 (4.0) l/min v 12.5 (2.6) l/min), while resting breathing was no more variable in the patients than in controls. The ventilatory response to carbon dioxide (VE/PCO2) was not significantly lower in the patients (14.9 (6.9) l/min/kPa) than in the controls (17.4 (4.3) l/min/kPa). Effort sensation responses to carbon dioxide driven breathing were similar in the control subjects and the patients. With regression analysis of pooled data neither maximum inspiratory pressure nor disease state contributed to perceived inspiratory effort during hypercapnia.

CONCLUSIONS

Moderately severe global respiratory muscle weakness does not appear to influence the ventilatory response to rising carbon dioxide tension or the perception of inspiratory effort in patients with dystrophia myotonica.

Sleep hypoxia in myotonic dystrophy and its correlation with awake respiratory function

BACKGROUND

Tiredness and daytime respiratory failure occur frequently in myotonic dystrophy. Sleep hypoxaemia was studied in 12 patients with myotonic dystrophy and correlations were sought with their daytime lung and respiratory muscle function.

METHODS

All patients underwent overnight sleep studies, clinical assessment, measurement of flow-volume loops and carbon monoxide transfer factor, arterial blood gas analysis, and physiological assessment of both thoracic muscle function and upper airways obstruction.

RESULTS

The mean nadir of oxygen saturation during sleep was 75% (95% confidence interval 69% to 81%). A mean of 3.4% of total sleep duration was spent at an oxygen saturation level below 85%. Five of the 12 patients had an apnoea index of > 5, the group mean apnoea/hypopnoea index being 15.8 events/sleep hour. The mean awake arterial oxygen tension (PaO2) was 10.7 kPa. There was a trend to hypercapnoea with a mean awake arterial carbon dioxide tension of 6.1 kPa; carbon dioxide retention worsened during sleep. Respiratory muscle dysfunction was mainly evident as a low maximum expiratory mouth pressure. Upper airway obstruction assessed by physiological criteria was found in four of the 12 patients. The proportion of total sleep duration with oxygen saturation levels below 85% was directly related to body mass index (weight/height2) and inversely related to the awake PaO2. Body mass index was inversely related to the overnight nadir of oxygen saturation.

CONCLUSIONS

Patients with myotonic dystrophy are often hypoxic during sleep and the subgroup that are obese, or have symptoms of sleep apnoea, or both, are particularly at risk. Sleep studies should be considered in this subgroup of patients with myotonic dystrophy.

Pulmonary function and resting breathing pattern in myotonic dystrophy

In 17 patients with myotonic dystrophy, spirometric, flow-volume, and maximal mouth occlusion variables were obtained and compared with 8 normal subjects. Ventilatory CO2 response was measured by the estimation of the steady-state effect of a sufficiently large serial dead space. Variability of resting breathing pattern was expressed by the variation coefficients of respiratory cycle time and tidal volume. The group means of the total lung capacity (TLC), vital capacity (VC), forced expiratory volume in 1 sec (FEV)1 and forced inspiratory volume in 1 sec (FIV)1 showed a restrictive pattern. Only maximal static mouth pressure (Pi,max), measured at residual volume (RV) level, showed a significant positive correlation with both VC (p = 0.03) and FIV1 (p = 0.02), suggesting inspiratory muscle weakness as a determinant of the restriction. Although the differences were just not significant, both variation coefficients of the respiratory cycle time and tidal volume were larger in the group with a CO2 sensitivity below the lower limit of normal compared to those with a normal ventilatory response to CO2. In 3 patients, fluctuations in FRC were also present. We hypothesize that, in addition to the already documented FRC fluctuations by uncoordinated spontaneous intercostal muscle action, a defect of integration of afferent neural input and chemical drive in the medullary region may also be present in these patients.

Cardiac anaesthesia in a patient with myotonic dystrophy

We describe a patient with myotonic dystrophy who required open-heart surgery for an atrial septal defect. He also had a sick sinus syndrome and an abnormal myocardium on histological examination. Anaesthesia using fentanyl, droperidol, nitrous oxide and a low concentration of enflurane was uneventful. Atelectasis of the left lung developed on the first postoperative day after removal of the tracheal tube. This was successfully treated by fibreoptic bronchoscopy.

Respiratory muscle strength and control of ventilation in patients with neuromuscular disease

To assess the relationship between respiratory mechanics and muscle strength and control of ventilation in patients with neuromuscular disease (NMD), we compared PImax and PEmax at RV, FRC and TLC, total respiratory elastance (Ers) with VT, TI, TT, VE, VT/TI, TI/TT, P.01, and P.01/(VT/TI) effective impedance in 21 patients with NMD and 21 healthy control (C) subjects, in seated position breathing room air. Ers in NMD patients was 79 percent higher than in the C subjects. While TI, TT, and VT in NMD were approximately half the corresponding C values, P.01 was 66 percent greater than in the C subjects (both p less than 0.001). NMD PImax and PEmax ranged from 37 to 52 percent of corresponding C values, respectively. Despite significant respiratory muscle weakness, only 7 of 16 patients demonstrated a PaCo2 greater than 45 mm Hg. Ventilatory output in NMD was modulated by respiratory mechanics as indicated by the increased P.01. In spite of muscle weakness, central drive in patients with NMD is not decreased, and in fact, is often increased. VE is not an accurate measure of central drive because of abnormal intrinsic respiratory mechanics and the effects of conscious responses or reflexes.

Obstetric anaesthesia in dystrophia myotonica

Two patients with dystrophia myotonica presented for urgent Caesarean section. Their per- and postoperative courses illustrate the anaesthetic problems posed by this disease. Respiratory difficulties are compounded by pregnancy and there is increased susceptibility to uterine haemorrhage. Choice of anaesthetic agent is discussed. Both had general anaesthetics; muscle relaxation was achieved with vecuronium.

[Anesthesia in myotonia]

Myotonia is defined as a persistent contraction of skeletal muscles after their stimulation. This contracture is not prevented or relieved by regional anaesthesia or muscle relaxants. The sensitivity to non-depolarizing muscle relaxants is usually normal. Suxamethonium, neostigmine, hypothermia, a rise in kalaemia should be avoided. There have been case reports of malignant hyperthermia in patients with myotonia congenita. Dystrophia myotonica is the second most frequent of the inherited muscle diseases, after Duchenne's dystrophy. The severity of the disease is due more to the muscular atrophy and the multiple organ involvement than to the abnormal contraction. Atrioventricular heart block and dysrhythmias are more common than heart failure. Prolonged apnoea and pneumonia are the main risks of anaesthesia. In severe cases, exists a restrictive respiratory insufficiency which is preceded by a fall in the maximum expiratory pressure. Dysphagias and inefficient coughing may occur early. An increased susceptibility to hypnotic drugs and opiates is a common feature. Spontaneous sleep apnoeas should be sought before anaesthesia, especially by using pulse oximetry. The anaesthetic implications are reemphasized.

Sleep-related breathing impairment in myotonic dystrophy

Respiratory failure has been described in myotonic dystrophy; it worsens during sleep but its central or peripheral origin has yet to be determined. Moreover, patients may present severely disturbed sleep and daytime somnolence. Eight patients with mild to moderate myotonic dystrophy were studied to assess breathing function while awake and during sleep by means of the pulmonary function tests, nocturnal polysomnographic examination and the multiple sleep latency test (MSLT). Three patients had restrictive respiratory defects; none had signs of airway obstruction. All patients had very disrupted nocturnal sleep. Of six patients who underwent the MSLT only two showed a mild tendency to sleep during the day. Six patients had pathological apnoea plus hypopnoea index [(A+H)I] and there was a prevalence of central apnoeas. The apnoeas occurred while resting but awake and throughout all sleep stages. Only two patients (the ones with the least vital capacity) had episodes of progressive oxygen desaturation during rapid eye movement sleep, similar to those found in other restrictive disorders and in chronic obstructive pulmonary disease. It is concluded that the breathing pattern characteristic of our myotonic dystrophy patients was the occurrence of central apnoeas both at rest while awake and during sleep.

Postoperative complications of dystrophia myotonica

A 44-year-old man with known mitral stenosis presented for minor surgery. Anaesthesia was induced with fentanyl, droperidol and etomidate and maintained with nitrous oxide, oxygen and vecuronium. Surgery and anaesthesia were uneventful but the postoperative course was stormy, with respiratory arrest, Haemophilus pneumonia, refractory cardiac dysrhythmias and gastrointestinal atony. A diagnosis of dystrophia myotonica was made after 3 weeks in the intensive care unit, and he spent 6 weeks in hospital. A high index of suspicion for this disease must be maintained and intensive care facilities and monitoring should be available for all procedures.

Aspiration pneumonia and coma--an unusual presentation of dystrophic myotonia

A 30-year-old female patient presented in a comatose state with clinical and radiographic signs of aspiration pneumonia 16 hours following elective surgery. Subsequent clinical assessment and investigations revealed the characteristic facies, proximal muscle weakness, lenticular opacities, pulmonary function defects, arterial desaturation and abnormal breathing during rapid eye movement (REM) sleep often associated with myotonia dystrophica. Although these characteristic features were evident on clinical examination postoperatively they were not noted in the preoperative assessment. The aspiration pneumonia and coma were unusual presenting features of this disease. Unsuspected myotonia dystrophica should be considered in the differential diagnosis of unexplained respiratory depression, aspiration or comatose state following surgery. Recognition of the disorder during the preoperative assessment is the key to avoiding complications during the perioperative management of such patients.

[Excessive daytime sleepiness, central type sleep apnea and myotonic dystrophy]

Two cases of myotonic dystrophy with excessive daytime somnolence are described. All-night polysomnographic studies were performed revealing high number of central sleep apnea which triggered micro-arousals and awakenings leading to decrease of sleep efficiency as well as of stage 3, 4 and REM. Obstructive and mixed apneas were found in the normal range. Hypoxia was not present in both recordings. Central sleep apneas and its secondary excessive daytime sleepiness may indicate early signs of the central nervous system impairment related to myotonic dystrophy, as a multi-organ disease.

Pulmonary function and ventilatory response to chemical stimuli in familial myopathy

We studied the pulmonary function and ventilatory response to carbon dioxide and hypoxia in three sisters aged 16, 13, and 10 years who presented with droopy eyelids, external ophthalmoplegia, hearing loss, speech difficulty, and truncal muscular weakness. Pulmonary function test results showed decreased maximum static pressure, reduced vital capacity and total lung capacity, normal functional residual capacity, elevated residual volume, and reduced dynamic pulmonary volumes. The degree of functional abnormality paralleled the severity of clinical manifestations. The characteristic picture of pulmonary functional abnormality was distinct from either restrictive disorders of pulmonary origin or obstructive pulmonary diseases. The ventilatory response to hypoxia was markedly diminished and hypercapnic response was moderately diminished in all three patients.

Dantrolene sodium and dystrophia myotonica

A patient with dystrophia myotonica was given dantrolene sodium to try to provide muscle relaxation during a cholecystectomy. Dantrolene was used as it is accepted that the drug has a place in the control of spasticity and also causes muscle relaxation, whereas conventional muscle relaxants are unable to control myotonia of muscle origin. Dantrolene alone did not provide good enough intubating and operating conditions in this subject. Later studies showed that, after dantrolene, EMG recordings from the patient were not significantly altered, although an impression of a slight increase in the myotonic potentials was gained.

Perioperative hazards in myotonic dystrophy

A 32-year-old man with myotonic dystrophy underwent a thoracotomy for removal of a mediastinal thymoma. Pre-operative examination revealed features of myotonic dystrophy, the only other abnormality was mild restrictive pulmonary disease. Anaesthesia was induced with thiopentone and maintained with enflurane, nitrous oxide, oxygen and curare. Following surgery, the patient was mechanically ventilated for several hours and remained intubated for 9 hours. The anaesthesia and surgery were tolerated well; however, postoperative complications included refractory dysrhythmias, hypoxia, pneumococcal pneumonia and pulmonary emboli. More intensive preoperative pulmonary evaluation and physiotherapy coupled with more aggressive postoperative pulmonary care might have resulted in a smoother recovery phase.

Cardiac abnormalities in myotonic dystrophy. Electrophysiologic and histopathologic studies

Eight young adult male patients with myotonic dystrophy, mean age 26 years, underwent 24-hour Holter electrocardiographic monitoring and intracardiac electrophysiologic study. Right ventricular endomyocardial biopsies were performed at the end of the electrophysiologic study in five of them. The atrial to His[A-H] interval was 155 msec in one case and less than or equal to 55 msec in all patients. Twenty-four hour Holter electrocardiographic monitoring demonstrated more than 4 premature ventricular contractions per minute in two patients and marked cyclical sinus arrhythmia during sleep in two others. Electron microscopic analysis of the endomyocardial biopsy specimens disclosed no prominent sarcoplasmic reticulum abnormalities but prominent I bands compared to previously obtained controls. Myofibrillar degeneration was seen in all cases and was associated with abnormal mitochondria in two. Cardiac abnormalities can be detected very early in the evolution of myotonic dystrophy, even prior to the onset of cardiac symptoms. The reported abnormalities appear closely related to the pathologic process affecting other skeletal muscles.

Baclofen trial in six myotonic dystrophy patients

Six young adult patients with grade I myotonic dystrophy and a complaint of daytime somnolence underwent 36-hour polygraphic monitoring, dynamometric and electromyographic studies before and under baclofen (60 mg/daily). Patients with the most severe daytime sleepiness had pathologic Sleep Apnea Indexes. After 6 weeks' ingestion of baclofen, no subjective or objective effect on patient symptomatology was found.

Acid maltase deficiency in adults presenting as respiratory failure

During the past nine years 10 patients with the adult form of acid maltase deficiency have been observed at the Mayo Clinic. Three of the adults presented with respiratory failure. In all three the respiratory manifestations dominated the clinical picture and the cause of the respiratory failure (muscle weakness) and the underlying myopathy (glycogen storage disease) were initially unsuspected. Careful evaluation of the respiratory function tests, including the maximal static respiratory pressures, electromyographic examination and histochemical and biochemical studies of muscle biopsy specimens eventually led to the correct diagnosis.

Blunted respiratory drive in congenital myopathy

Two patients with clinically mild congenital myopathies presented with chronic respiratory failure. Muscle weakness alone could not account for the respiratory insufficiency since static respiratory pressures were not markedly impaired, ventilation during exercise was normal, and daytime ventilation was normal if ventilatory assistance was provided at night. The ventilatory responses to inhaled carbon dioxide were very low, suggesting that impairment of the central nervous respiratory chemoreceptor contributed to hypoventilation. These patients and others described in the literature suggest that central depression of ventilation may occur more frequently than previously recognized in patients with muscular disorders. Patients with chronic respiratory failure due to central depression of respiratory drive can be effectively managed by assisted ventilation at night.

Respiratory failure and cardiac disturbances in myotonic dystrophy

Cardiopulmonary abnormalities are frequently encountered in myotonic dystrophy. We present five patients with myotonic dystrophy who entered the intensive care unit in acute respiratory failure. The possible etiologic factors of pulmonary complications are reviewed. The most important is probably aspiration pneumonia. The difficulties in the treatment of the respiratory failure are emphasezed. Myotonia of the chest muscles and diaphragm make artificial ventilation difficult. Recovery is delayed chiefly by swallowing disturbances. General anaesthesia is hazardous. Four patients presented cardiac arrhythmias and/or conduction abnormalities which were transient.

Alveolar hypoventilation and hyperosmnia in myotonic dystrophy

A case of myotonic dystrophy accompanied by alveolar hypoventilation and hypersomnia is presented. Radiological studies and EMG examination of the intercostal muscles demonstrated that the respiratory muscles were affected by the disease, while polygraphic recordings showed that the alveolar hypoventilation and pulmonary hypertension worsened during sleep. The hypersomnia preceded the appearance of clinical signs of the muscular disease by many years and persisted even after treatment when the blood gas analysis values were greatly improved. During both diurnal and nocturnal sleep, the patient frequently fell asleep directly into a REM stage. The possibility is discussed that, concomitant with the respiratory musculature involvement, there is an alteration in the central nervous system in myotonic dystrophy which is at least partially responsible for both the alveolar hypoventilation and the hypersomnia.