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).