Nonspecific Interstitial Pneumonia (NSIP) is a lung condition affecting the interstitium, the delicate network of tissue supporting the lung’s air sacs. It is considered an “idiopathic interstitial pneumonia,” meaning its cause is unknown.
Defining Nonspecific Interstitial Pneumonia
NSIP is a chronic condition characterized by inflammation and scarring (fibrosis) within the lung’s interstitium. This damage affects the lung tissue diffusely and uniformly. Unlike common pneumonia, which inflames the air sacs, NSIP impacts the supporting tissue.
NSIP is part of interstitial lung diseases (ILDs), which involve inflammation and scarring in the lung’s supporting tissue. It is labeled “nonspecific” because its microscopic features do not align with specific patterns observed in other ILDs. The inflammation and fibrosis are often spread evenly throughout the affected lung tissue, rather than appearing in patchy areas.
The Unique Hallmarks of NSIP
A defining characteristic of NSIP is its homogeneous interstitial fibrosis and inflammation, observed under a microscope. This means changes in lung tissue appear uniform across affected areas, unlike the patchy damage seen in other interstitial lung diseases. This uniformity helps distinguish NSIP from conditions like usual interstitial pneumonia (UIP), which presents with varied stages of scarring.
Pathologists identify two main patterns: cellular and fibrotic. The cellular pattern shows more inflammation and less scarring, while the fibrotic pattern indicates more extensive scarring. Neither pattern exhibits the prominent fibroblastic foci common in other idiopathic interstitial pneumonias, highlighting NSIP’s unique microscopic appearance. The cellular pattern generally suggests a more favorable outlook.
Causes and Symptoms of NSIP
NSIP can be “idiopathic,” meaning it arises without a clear cause. However, it is also associated with other medical conditions, making it a “secondary” form. Common associations include connective tissue diseases like scleroderma, rheumatoid arthritis, and lupus. Other associations include HIV infection and lung damage from certain medications such as amiodarone, methotrexate, or nitrofurantoin.
Patients typically experience a persistent, often dry cough and shortness of breath (dyspnea). These symptoms develop gradually over weeks to months and can worsen over time. Fatigue is also common, and individuals with associated connective tissue diseases might experience joint pain, dry eyes, or skin changes.
How NSIP Is Diagnosed
Diagnosing NSIP involves a comprehensive approach, combining medical history, physical examination, and advanced imaging. High-resolution computed tomography (HRCT) scans of the chest are an important imaging tool. On HRCT, doctors look for specific patterns like ground-glass opacities (hazy areas) and reticulation (fine lines).
A lung biopsy (surgical or transbronchial) is often performed to confirm the diagnosis and rule out other interstitial lung diseases. This procedure allows a pathologist to examine lung tissue samples for characteristic features. Excluding other known causes for lung changes is an important step in establishing an NSIP diagnosis.