Cough as a neurological sign: What a clinician should know

Table 1 Neurological conditions associated with increased cough reflex sensitivity and its mechanism

Disorder		Mechanism
Cerebral disorders	Psychogenic causes: Somatic or “tic” cough, Tourette's syndrome	(1) Peer and familial psychosocial stress; and (2) Mediated in part by the dopaminergic activity
	Primary central reasons: (1) Medullary lesion: Chiari I malformations; (2) Space-occupying lesion; and (3) Neuromyelitis Optica spectrum disorder	(1) Lesions in the dorsal medullary region of the brainstem; (2) Irritation of the cough center; and (3) Autonomic dysregulation secondary to loss of parasympathetic innervation
Cerebellar disorders	Cerebellar neurodegenerative disorders e.g., autosomal dominant cerebellar ataxia	Lesions in deep cerebellar nuclei which are engaged in neural activities necessary for breathing and coughing causing laryngeal hyperreactivity and vagal dysfunction
Vagal neuropathy	Viral infections	Induction of persistent plasticity in the neural pathways mediating cough with activation of the cough-evoking sensory nerves that innervate the airway wall
	Irritant exposure	Irritation of the rapidly adapting irritant receptors, located mainly on the posterior wall and the carina of the trachea, and pharynx
	Chronic conditions such as asthma	Due to Airway vagal hypertonia
	Vitamin B12 deficiency	Damages the myelin sheath and axonal degeneration

Table 2 Neurological conditions associated with diminished cough reflex sensitivity

Category
Cerebral disorders	Brain hypoxia
	Cerebrovascular events
	Dementia
	Parkinson’s disease
	Drugs: e.g., antipsychotic drugs, anaesthetics
Amyotrophic lateral sclerosis and multiple sclerosis
Neuromuscular diseases: e.g., myasthenia gravis
Peripheral neuropathy	Hereditary sensory autonomic neuropathies
	Phrenic nerve palsy or injury
	Diabetic autonomic neuropathy
	Vitamin B12 and folate deficiency