Why does a patient's cough worsen at night, potentially indicating an underlying respiratory condition such as asthma (Asthma) or Chronic Obstructive Pulmonary Disease (COPD), or Gastroesophageal Reflux Disease (GERD)?

Why Cough Worsens at Night

Cough worsens at night primarily due to physiological changes that occur during sleep and recumbency, including increased airway inflammation peaking at 4:00 AM, reduced circulating epinephrine levels, increased vagal tone, and the supine position facilitating gastroesophageal reflux—not because sleep itself causes cough, as cough typically ceases once patients fall asleep. 1, 2, 3

Physiological Mechanisms of Nocturnal Cough

Circadian Rhythm Effects in Asthma

• Airway inflammation and obstruction peak at 4:00 AM in asthmatic patients, with nighttime peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) significantly reduced compared to daytime values 2, 3
• Up to 74% of asthma patients experience nocturnal symptoms leading to awakening at least once weekly, and up to 80% of fatal asthma attacks occur overnight or early morning 2, 3
• Circadian rhythms influence inflammatory cell activation, hormone levels (particularly lower epinephrine at night), and increased cholinergic/vagal tone during sleep hours 3

The Sleep Paradox

• Cough is unlikely to occur once patients actually fall asleep, regardless of whether the cause is chronic bronchitis, gastroesophageal reflux disease (GERD), or asthma 1, 2
• Cough occurs more commonly during wakefulness compared to sleep, and the absence of nocturnal coughing should not be used to suggest psychogenic cough or definitively rule out GERD 1
• This means the "nocturnal" worsening typically refers to evening hours and early morning awakening, not continuous coughing throughout sleep 1, 2

Differential Diagnosis: Not Just Asthma

GERD as a Major Contributor

• GERD is a common cause of nocturnal cough and wheeze in both children and adults, as the supine position facilitates acid reflux into the esophagus and potentially the airways 2, 4, 5
• Increased nocturnal cough has been objectively documented in patients with gastroesophageal reflux 2
• GERD may be asymptomatic (no heartburn or regurgitation), making it a frequently missed diagnosis in patients with isolated nocturnal cough 5

Other Important Causes

• Sleep-disordered breathing and snoring disorders are associated with increased nocturnal cough and wheeze 2, 4
• Only one-third of children with isolated nocturnal cough or wheeze actually have an asthma-like illness, emphasizing the importance of considering alternative diagnoses 2, 4, 6
• Multiple conditions including protracted bacterial bronchitis can present with identical nocturnal patterns 2, 4

Critical Clinical Pitfall

The timing or character of cough (including nocturnal predominance) is not helpful in predicting its cause and should never be used as the sole basis for diagnosis. 1, 2

• The American Thoracic Society explicitly states that neither the character of cough (wet, dry, paroxysmal) nor the timing (nocturnal, with meals) reliably predicts etiology 1
• Nocturnal symptom reporting by patients correlates poorly with objective cough counts (Cohen's kappa 0.3), making subjective reports unreliable 2

Diagnostic Approach for Nocturnal Cough

Initial Evaluation

• Look for variable expiratory airflow limitation and symptoms that vary over time and intensity, including daytime symptoms such as wheeze, shortness of breath, chest tightness, and exercise limitation 2, 4
• Perform spirometry with bronchodilator response if age-appropriate (≥12% and ≥200 mL increase in FEV1 indicates reversibility) 1, 4
• Assess for GERD by asking about gastrointestinal symptoms and consider 24-hour pH monitoring if suspicion is high 2, 4
• Evaluate for sleep-disordered breathing by asking about snoring, witnessed apneas, and restless sleep 2, 4

When Asthma is Confirmed

• Cough worse at night is listed as a diagnostic criterion for asthma, along with symptoms occurring or worsening at night and awakening the patient 1
• However, diagnosis requires objective confirmation (spirometry showing obstruction with reversibility, or positive methacholine challenge), not just the presence of nocturnal symptoms 1, 4, 6

Treatment Implications

• For confirmed asthma with nocturnal symptoms, inhaled corticosteroids are first-line therapy, potentially with long-acting beta-agonists 4, 7
• For GERD-related nocturnal cough, start with antireflux diet and lifestyle modifications plus a proton pump inhibitor (PPI), noting that response time is highly variable (2 weeks to several months) 2
• Upper airway cough syndrome (postnasal drip) and asthma typically respond within 1-2 weeks, while GERD may require several months of treatment 2