Neuromuscular Disorders

Abstract

In children with both inherited and acquired neuromuscular disorders (NMD) deterioration of the respiratory function contributes to relevant morbidity and is often responsible for a high mortality with these diseases. Respiratory manifestation of NMD depends on the pattern of muscle and/or nerve involvement and the rate of progression. Some NMD have little or no respiratory involvement whereas others present with a continuous deterioration of the respiratory system. The latter is the rule in the most common pediatric NMD, Duchenne muscular dystrophy, spinal muscular atrophy and congenital muscular dystrophies. But it is important to be aware that some disorders may present with considerable asynchrony in trunk and limb muscular weakness on the one hand and respiratory muscle weakness on the other hand. Hence, patients who are still ambulatory may present with unsuspected respiratory complications. Normally, chronic respiratory muscle failure develops slowly over a period of several years. Initially, it presents with disordered breathing apparent only during sleep, followed by continuous progression to severe hypoventilation, cor pulmonale and eventually frank respiratory failure in end-stage disease. In patients with preexisting respiratory compromise respiratory failure may also present acutely, in most cases as a result of a chest infection. The use of the respiratory function testing in neuromuscular patients has been investigated extensively and many tests have proven to be helpful. However, most studies have been done in adolescents with Duchenne muscular dystrophies and adults with other neuromuscular conditions. But there has been only very little research on how to assess respiratory function in infants and toddlers with NMD. In fact, assessing and interpreting respiratory function in young children is often difficult. This is above all due to the patients’ limited cooperation but also to a lack of standardized-test normative data for respiratory function testing other than the measurement of lung volumes. Other difficulties may occur in connection with underlying disabilities of the children such as facial dysmorphia with an inability of mouth closure, bulbar and swallowing dysfunction or an inability of unassisted sitting in a body chamber. Distribution and severity of respiratory muscle involvement differs in distinct NMD, may change in the individual patient over time and often deteriorates during sleep. Respiratory function testing should make it possible to differentiate between inspiratory and expiratory muscle weakness and/or upper airway muscle involvement. Therefore, wherever feasible, basic evaluation should include assessment of pulmonary function, inspiratory and expiratory muscle strength and peak cough flow. It is important to recall that results of respiratory function testing vary considerably in how they are ultimately affecting breathing and gas exchange.Therefore, in patients with pathological respiratory function testing advanced evaluation should include an examination of the breathing pattern and blood gases during wakefulness and sleep.A sleep study with continuous recording of respiration, oxygen saturation and carbon dioxide tension is the most valuable single test, though expensive. Moreover, it makes possible the assessment of respiratory function in children who are not able to cooperate in classic respiratory function testing. Given that NMD patients are at high risk of respiratory complications frequent and early evaluation is crucial.Where possible patients should be diagnosed and treated in an interdisciplinary approach including pediatric neurologists, pulmonologists, orthopedics and physiotherapists with thorough training in pediatric NMD. The aim of periodic respiratory assessment is to detect respiratory malfunction and to predict complications on time. It is coupled with a consequent therapeutic program aimed to prevent and treat respiratory complications. This chapter will review the respiratory disturbances in different NMD, discuss the indications and clinical value of respiratory function testing and describe the assessment and interpretation of respiratory function testing in children with NMD.