Pulmonary-renal syndrome is almost always caused by an autoimmune disorder.
Diagnostic testing involves urinalysis, blood tests for certain proteins (antibodies) that indicate the body is reacting to its own tissues, and sometimes analysis of tissue from a lung or a kidney.
Treatment requires corticosteroids and often cyclophosphamide (a chemotherapy drug) or rituximab and other drugs that suppress the body's immune system.
An important function of the immune system is fighting off infections. To do this, the immune system recognizes microorganisms as foreign to the person and produces proteins (antibodies) that join with the microorganisms so they can be removed from the body. In autoimmune disorders, the body mistakenly reacts against a person's own tissues as if they were foreign. In autoimmune disorders that involve the lungs, the immune system attacks and damages lung tissue. Autoimmune disorders that affect the lungs also often affect other organs, particularly the kidneys.
Pulmonary-renal syndrome is a syndrome, rather than a specific disorder. A syndrome is a group of symptoms and other abnormalities that occur together but may be caused by several different disorders or even other syndromes. Pulmonary-renal syndrome involves a lung disorder called diffuse alveolar hemorrhage, which is widespread damage to the small blood vessels that supply the lungs, causing blood to accumulate in the lung's tiny air sacs (alveoli). People also have a type of kidney problem called glomerulonephritis, a disorder of glomeruli (clusters of microscopic blood vessels in the kidneys with small pores through which blood is filtered). Glomerulonephritis is characterized by body tissue swelling (edema), high blood pressure, and the presence of red blood cells in the urine.
Pulmonary-renal syndrome can be caused by various disorders.
The most common causes of pulmonary-renal syndrome are autoimmune disorders such as
Systemic lupus erythematosus (lupus)
Less common autoimmune causes include
Typical symptoms include
Occasionally symptoms are severe enough to cause the lungs to fail (respiratory failure), and people have severe difficulty breathing and bluish discoloration of the skin (cyanosis). When the lungs fail, the tissues of the body do not receive enough oxygen, and the person may die.
Kidney involvement causes blood in the urine, but if the amount is very small, blood may not be visible. Kidney involvement also causes blood pressure to increase. The symptoms related to the lungs and the kidneys may not occur at the same time.
Sometimes the disease may have sudden flare-ups.
Doctors can often diagnose diffuse alveolar hemorrhage by a person's symptoms and chest x-ray findings. Chest x-rays typically show abnormal white patches in the lungs caused by lung bleeding. If the diagnosis is not clear based on symptoms and chest x-ray findings (for example, if the person has not coughed up blood), doctors may need to insert a flexible viewing tube into the lungs (bronchoscopy) and wash out the lungs with fluid (bronchoalveolar lavage) to check for blood.
The level of red cells in the blood is measured to test for anemia.
Glomerulonephritis is diagnosed by symptoms, urinalysis, and blood tests of kidney function.
Once pulmonary-renal syndrome has been diagnosed, doctors try to determine the cause. They order blood tests for antibodies directed against the person's own tissues (called autoantibodies). If test results do not reveal the cause, doctors may need to remove a small piece of lung or kidney tissue for analysis (biopsy).
In most people, pulmonary-renal syndrome is caused by an autoimmune disorder, so treatment typically requires high doses of corticosteroids (such as prednisone) to suppress the immune system. If people are very ill, they are often also given cyclophosphamide to further suppress the immune system. Rituximab may be used instead of cyclophosphamide.
Plasma exchange—a procedure in which the unwanted antibodies are removed from the blood—is often helpful.