Estimates of the overall prevalence of clinically significant ILD have ranged from 25 to 74 per 100.000 population, and up to 80.9 per 100,000 in men and 67.2 per 100,000 in women. The overall incidence of 31.5 per 100,000 in men and 26.1 per 100.000 in women with IPF and other pulmonary fibrotic diseases accounts for > 45% of the diagnoses. Clinically, significant cough occurs in > 80% of IPF patients, although the percentage of those in whom the symptom was solely or primarily due to IPF is unknown.
The pathogenesis of cough in the most common of the ILDs, IPF, has been investigated. In a well-conceived and well-performed study, nonsmoking patients with a confirmed diagnosis of IPF in whom airway hyperresponsiveness, chronic rhinitis, and gastroesophageal reflux were excluded, there was an increased sensitivity to substance P and capsaicin, and increased sputum levels of nerve growth factor and brain-derived neurotrophic factor, suggesting a functional up-regulation of sensory neurons of the lung. Restrictive physiology with increased deposition of aerosolized particles does not appear to play a role. While the lack of control patients with other causes of cough may limit the specificity of these findings, they offer new insight with potential therapeutic implications. Click Here
The pathogenesis of cough in other types of ILD are less well-understood; however, many of them appear to have predictable causes, for example, inflammatory changes of the airways both large and small are often affected in rheumatoid arthritis-related ILD, reversible airflow limitation is commonly seen in eosinophilic pneumonias, and chronic sinus and airways disease is a regular finding in Churg-Strauss vasculitis. A specific diagnosis of the ILD is required as therapeutic interventions and outcome may differ significantly based on the underlying disease. A diagnosis may occasionally be made on the basis of characteristic findings on the necessarily comprehensive medical history, physical examination, pulmonary physiologic studies (eg, lung volumes, spirometry, and gas exchange), and radiographic studies (ie, chest radiographs [CXRs] and high-resolution CT (HRCT) scans).