Motor Neuron Diseases:
Motor neuron disease is a neurological degenerative disorder affecting the corticospinal tracts, the motor nuclei in the brainstem, and the anterior horn cells of the spinal cord. It reduces the ability to cough efficiently. In the early stages, there is a hyperactive cough reflex due to the presence of inflammatory mediators such as bradykinin and prostaglandins. As the disease progresses, there is continuous damage that causes desensitisation of the cough. Various combinations of upper and lower motor neuron dysfunction can enhance the cough stimulus, but unfortunately, impair the efficiency of both volitional and reflex cough types (37). Amyotrophic lateral sclerosis is characterised by degeneration of the upper (UMN) and lower motor neurons (LMN), which negatively affects the ability of the respiratory and laryngeal muscles to work harmoniously during cough phases. The presence of stiffness due to UMN degeneration and weakness due to LMN degeneration results in abnormal cough flow and impaired ability to clear the airway, leading to various pulmonary sequelae, recurrent pneumonia, and even respiratory failure (38). The voluntary cough test detects the presence of dysphagia and impaired physiological capacity of airway clearance and secretion management (39).