Nonspecific Interstitial Pneumonia

Etiology, Prevalence, and Epidemiology

Nonspecific interstitial pneumonia (NSIP) is a chronic interstitial lung disease characterized by homogeneous expansion of the alveolar walls by inflammation or fibrosis or both. NSIP is the second most common chronic interstitial pneumonia, after usual interstitial pneumonia (UIP), accounting for 14% to 35% of cases. NSIP may be idiopathic but more commonly occurs as a manifestation of connective tissue disease, hypersensitivity pneumonitis, drug-induced lung disease, and chronic interstitial lung disease complicating diffuse alveolar damage.

The prognosis of NSIP is influenced by its predominant histologic component. Patients with a predominantly or exclusively inflammatory component (i.e., cellular NSIP) have an excellent prognosis with few reported deaths, whereas the reported median survival of patients with fibrotic NSIP ranges from approximately 6 to 14 years. The prognosis of NSIP is considerably better than the prognosis of idiopathic pulmonary fibrosis (IPF), the clinical condition most commonly associated with UIP.

Clinical Presentation

The median age of onset of symptoms in NSIP is 40 to 50 years, which is more than 10 years younger than patients with IPF. NSIP may occur in childhood and in the elderly, however, having been reported in patients 9 to 78 years old. The symptoms, similar to those of IPF, consist of progressive dyspnea and dry cough with a duration ranging from 6 months to 3 years before diagnosis. Finger clubbing occurs in 10% to 35% of patients, which is less common than in patients with IPF. Auscultation reveals basal or widespread crackles.

Pathophysiology