Which condition could be causing a cough that worsens when the patient is supine?

A cough that worsens when the patient is in a supine position is often associated with gastroesophageal reflux (GERD). In this condition, stomach acid can flow back into the esophagus, especially when lying down, leading to irritation of the lining and triggering a cough reflex.

When a patient is supine, the angle of the esophagus relative to the stomach can allow for easier reflux of gastric contents. The acid can irritate the throat and airways, resulting in a cough that is exacerbated in this position. This is particularly pronounced at night; many patients with GERD report nocturnal coughing, which can disrupt sleep.

While asthma can cause coughing, it typically does not have a positional component directly tied to lying down. Pneumonia can present with cough, but it usually manifests with additional systemic symptoms such as fever and is often independent of position. Chronic postnasal drip may cause a cough that worsens with certain positions, but it is less specifically linked to the supine position compared to GERD.

Thus, the position-dependent worsening of the cough strongly suggests gastroesophageal reflux as the underlying cause.