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Congenital nemaline myopathy recommendations for the care of patients

Carina Wallgren-Pettersson, M.D., Ph. D., Consultant in Medical Genetics, Co-convenor of the EMNC International Consortium on Nemaline Myopathy

Clinical summary
Congenital nemaline myopathy is characterised by generalised muscle weakness from birth or infancy. The diagnosis is confirmed by a muscle biopsy, which reveals the presence of threadlike nemaline bodies (Greek nema = thread) in the muscle tissue, and often predominance of slow (type 1) muscle fibres. The respiratory muscles are often especially weak, which leads to restricted respiratory capacity. Cardiac contractility is normal, and involvement of the cardiac muscle is very rare. An initial cardiac evaluation is however indicated because of the very rare cases with cardiomyopathy. There is also no evidence of smooth muscle involvement. No abnormalities of the central nervous system have been documented. The prognosis is largely dependent on the on the maintenance of muscle power and respiratory capacity, and the prevention of scoliosis and other detrimental contractures. Both an autosomal dominant and an autosomal recessive form of nemaline myopathy exist, and the two may be indistinguishable on clinical grounds in the individual patient. Mutations in one of at least six different genes can cause nemaline myopathy. Thus, consultation with a specialist in Medical Genetics is recommended.

Follow-up
Respiratory capacity requires monitoring, chest physiotherapy and assisted coughing are mandatory, and infections should be treated vigorously. Special attention should be paid to possible signs of nocturnal hypoxia. If forced vital capacity decreases to below 60%, annual sleep polysomnography studies are necessary. If it decreases below 40 %, there is a significant risk of nocturnal hypoventilation. Thus, polysomnography should be performed more often, and treatment initiated where required. Cardiac follow-up is indicated because of the risk of cor pulmonale. Evidently, smoking endangers the small respiratory capacity even further, and should be strongly discouraged. Guidelines for ventilatory management are given in Wallgren-Pettersson et al. 2004, ref. below.

Swallowing difficulties are common and may require intervention to prevent aspiration. Should scoliosis develop, early operation is preferable to bracing because of the further restriction of respiration caused by bracing. Other contractures should be treated conservatively but as actively as possible to avoid surgical interventions requiring immobilisation. It is clear that complete immobilisation of a limb for any length of time leads to irreversible atrophy of the muscle in that limb. If surgical intervention is necessary for any reason, rapid postoperative mobilisation is important.

Physiotherapy
All patients with nemaline myopathy are likely to benefit from physiotherapy, provided it is given by a physiotherapist familiar with the treatment of neuromuscular disorders. It should include maintenance of muscle strength and range of movements, prevention of scoliosis and back pain, assisted coughing and maintenance of respiratory capacity, mobility and independence in the activities of daily living. Physiotherapy should be maintained during any periods of hospital treatment, and used to prevent the detrimental effects of any immobilisation. Cardiorespiratory exercises recommended are endurance training, e.g. swimming, and regular breathing exercises using assisted coughing.

Anaesthesia
No anaesthetic complications have been reported. Nevertheless, muscle relaxants are best avoided, and benzodiazepines should be used with caution because of their potentially adverse effect on breathing and muscle power.

Occupation
The patient should be encouraged to choose an occupation free from physical strain, high risk of infection, and exposure to tobacco smoke and other toxic agents.

Pregnancy care

Pregnancy
Many patients have gone through pregnancy and delivery without problems. Nevertheless, the pregnancies of affected women should be followed carefully by the Neurologist and Obstetrician caring for the patient. Special consideration should be afforded the patient's respiratory capacity, muscle weakness and any contractures potentially complicating delivery. Although involvement of smooth muscle has not been reported, the process of labour needs to be planned carefully and managed individually.

Useful links

• Pregnancy in a patient with nemaline myopathy
• Pregnancy and delivery in congenital nemaline myopathy
• See also a list of publications on pregnancy with a disability.
• Nemaline myopathy and pregnancy: A challenge indeed. Scroll down the page. No need to download.