Cough in motor neuron disease: a review of mechanisms.

Abstract

For patients with neuromuscular diseases which affect breathing and swallowing, coughing and choking are frightening and distressing symptoms sometimes perceived (correctly) as life-threatening. Cough is an important function of the larynx and respiratory system which allows an individual to clear the airway of foreign material and secretions and prevent aspiration of food and fluid. Choking is the feeling of strangulation or suffocation which may result from the presence of foreign material in the airway, often accompanied by airway obstruction so that there is an inability to draw breath. Motor neuron disease (MND) is a progressive degenerative disorder of the nervous system affecting the anterior horn cells of the spinal cord, the motor nuclei of the brain stem, and the corticospinal tracts. For MND patients, airway obstruction, aspiration and pneumonia are major causes of morbidity and mortality; episodes of coughing and choking are commonly reported by patients, and presumably represent episodes of decompensation of bulbar and respiratory mechanisms as progressive dysfunction develops. Such patients have, on the one hand, an increased need to cough but, on the other, a reduced capacity to do so effectively. To try to develop a clearer clinical approach to dealing with these symptoms, we review some aspects of cough and, subsequently, its pathophysiology in MND. The cough reflex is divided into three main elements: the sensory limb, the central control, and the efferent limb (Figure 1). Figure 1. The cough reflex. ### Sensory limb The epithelium of the larynx, trachea, and larger bronchi contains sensory nerves that are responsible for triggering cough. There are two main categories of cough receptors: the rapidly-adapting pulmonary stretch receptors (RAR) with small-diameter myelinated fibres, and the pulmonary and bronchial C fibre receptors with non-myelinated afferent fibres.1 The pattern of cough depends on the stimulus and on the part of the respiratory tract stimulated. Receptors … Dr S. Hadjikoutis, Department of Neurology, University Hospital of Wales, Heath Park, Cardiff CF4 4XN