Systemic Lupus Erythematosus (SLE), or lupus, is a chronic autoimmune disease where the body’s immune system mistakenly attacks its own healthy tissues and organs. The term “systemic” indicates that the disease is not confined to a single area but can cause widespread inflammation and damage throughout the body. Lupus can affect almost any organ system, including the skin, joints, kidneys, and nervous system. The respiratory system is frequently involved, with estimates suggesting that lung-related issues affect a large percentage of patients over the course of their disease.
Inflammation of the Lung Lining (Pleurisy)
The most common way lupus affects the chest is through inflammation of the pleura, a condition called pleurisy or pleuritis. The pleura consists of two thin, double-layered membranes: one lining the chest cavity and the other covering the lungs. These layers normally glide smoothly over one another during breathing, aided by lubricating fluid.
When lupus causes inflammation, the normally smooth pleural surfaces become rough and irritated. This irritation results in a sharp, stabbing chest pain that characteristically worsens with deep breathing, coughing, or sneezing. This pleuritic chest pain is a hallmark symptom and often occurs during a generalized lupus flare. The inflammation can also cause fluid to build up between the pleural layers, a complication known as pleural effusion.
The presence of this fluid can further restrict lung movement and lead to shortness of breath. While pleurisy is manageable with anti-inflammatory medications and often resolves without permanent damage, it can be a recurrent manifestation of SLE. Up to half of all people with SLE may experience pleurisy at some point.
Direct Inflammation and Scarring of Lung Tissue
Beyond the lining, lupus can directly target the lung parenchyma, the functional tissue responsible for gas exchange, leading to two distinct forms of damage. The most immediate and life-threatening form is Acute Lupus Pneumonitis (ALP), a severe inflammatory condition. ALP is rare, affecting an estimated 1% to 10% of patients, but it represents a serious medical emergency.
This acute inflammation presents with severe shortness of breath, chest pain, fever, and a cough that may involve coughing up blood. The underlying pathology involves damage to the air sacs and surrounding structures, which can be challenging to distinguish from a severe infection. Survivors of an acute episode may be left with residual scarring, contributing to long-term breathing problems.
In contrast, Chronic Interstitial Lung Disease (ILD) is a progressive form of lung damage that develops subtly over time. Autoimmune inflammation causes the tissue between the air sacs, known as the interstitium, to thicken and scar. This scarring, or fibrosis, makes the lungs stiff and less elastic, restricting their ability to expand fully.
The thickening of the lung tissue increases the distance oxygen must travel to enter the bloodstream, resulting in reduced oxygen transfer efficiency. People with chronic ILD experience a gradual onset of shortness of breath, particularly with physical exertion, and a persistent dry cough. Chronic ILD can develop independently or as a long-term consequence of ALP, causing significant long-term disability and reduced lung function in SLE.
Mechanical Restriction (Shrinking Lung Syndrome)
A less common but distinct complication of SLE is Shrinking Lung Syndrome (SLS), which involves mechanical restriction rather than primary tissue inflammation. SLS is characterized by a progressive reduction in lung volumes, making it difficult to take a full, deep breath. This restriction is diagnosed by pulmonary function tests showing a restrictive pattern and chest imaging revealing an elevated position of the diaphragm.
The underlying issue is believed to be weakness or dysfunction of the diaphragm, the large muscle below the lungs that drives respiration. Unlike other lupus lung conditions, the lung tissue itself may appear healthy, without significant scarring or active inflammation. The compromised movement of the diaphragm restricts the chest cavity’s ability to expand, preventing the lungs from inflating completely.
Symptoms of SLS are limited to shortness of breath, which worsens over time, and non-pleuritic chest pain. This condition is important to recognize because its mechanism is unique among lupus lung complications, focusing on musculoskeletal involvement rather than direct parenchymal damage. Although rare, effective treatment targeting the underlying autoimmune activity can stabilize or even improve lung function.
Damage to Pulmonary Blood Vessels
Lupus can also target the vessels that carry blood through the lungs, leading to Pulmonary Hypertension (PH). PH is defined as abnormally high blood pressure within the arteries of the lungs. This increased pressure forces the right side of the heart to work harder, which can eventually lead to heart failure if left untreated.
Pulmonary hypertension in SLE can occur through several pathways. The most direct is inflammation of the vessel walls, known as vasculitis. This inflammation can cause the small pulmonary arteries to narrow and stiffen, a specific form classified as Pulmonary Arterial Hypertension (PAH). Lupus-related PAH is a severe complication that affects a small percentage of patients, with estimates ranging from 0.5% to 9%.
PH can also develop secondarily due to other lupus complications. For example, chronic blood clots traveling to the lungs, a risk increased by certain lupus-related antibodies, can obstruct blood flow and raise pressure. Chronic scarring from interstitial lung disease can also destroy blood vessels, forcing the remaining vessels to handle a higher volume of blood and increasing pressure. The symptoms of PH, such as progressive shortness of breath and fatigue, are non-specific, making early diagnosis challenging but important for improving the long-term outlook.