Diffuse alveolar hemorrhage, or DAH, is a medical syndrome characterized by widespread bleeding into the alveoli—the tiny air sacs where the lungs exchange oxygen and carbon dioxide—which disrupts this process. This bleeding originates from the lung’s smallest blood vessels, including capillaries, arterioles, and venules. DAH is a serious condition that requires prompt medical evaluation and care.
Underlying Causes and Triggers
The most frequent cause of DAH is an underlying autoimmune disease. In these conditions, the body’s immune system incorrectly targets and damages the small blood vessels in the lungs, a process known as pulmonary capillaritis. Examples include granulomatosis with polyangiitis and microscopic polyangiitis, where inflammation of blood vessels, or vasculitis, is a primary feature. Goodpasture syndrome is another cause, involving antibodies that attack the basement membranes of capillaries in both the lungs and kidneys. Systemic lupus erythematosus (SLE) is also a recognized connective tissue disorder that can lead to DAH.
Certain heart conditions can also trigger DAH. For instance, severe mitral stenosis, a narrowing of the heart’s mitral valve, can impede blood flow and cause a significant rise in pressure within the pulmonary blood vessels. This elevated pressure can strain the delicate capillaries, leading to blood leaking into the alveolar spaces. This type of hemorrhage is sometimes referred to as ‘bland’ because it occurs without the vessel inflammation seen in autoimmune causes.
Certain medications and inhaled substances have been linked to DAH. Some anticoagulants, antiplatelet agents, and drugs used to break up blood clots can precipitate bleeding. Other medications, such as propylthiouracil, methotrexate, and nitrofurantoin, have also been identified as potential triggers. The inhalation of toxins, including substances like crack cocaine or certain pesticides, can cause direct injury to the lung’s microvasculature, resulting in hemorrhage.
Less commonly, DAH can arise from other conditions. Severe lung infections can sometimes lead to bleeding within the alveoli. Disorders that affect blood clotting (coagulopathies) can also be a cause. Furthermore, DAH is a known, though infrequent, complication following bone marrow transplantation.
Recognizing the Signs
The presentation of diffuse alveolar hemorrhage often includes a distinct combination of symptoms. One of the most recognized signs is hemoptysis, or coughing up blood, which can range from pink-tinged, frothy sputum to pure blood. However, hemoptysis may be absent in up to a third of patients, as a large volume of blood can accumulate in the lungs before being coughed up.
A sudden onset of shortness of breath (dyspnea) is another common sign. This leads to a feeling of breathlessness that can worsen rapidly. Patients may also experience a fever and chest pain along with breathing difficulties.
Significant blood loss into the lungs leads to anemia, a deficiency of red blood cells. The resulting anemia can cause symptoms such as persistent fatigue, pale skin, and a general feeling of weakness.
Diagnostic Process
Diagnosis begins with a physical examination and a review of the patient’s medical history. A doctor will listen to the lungs with a stethoscope for any abnormal sounds that might suggest fluid accumulation.
Imaging studies are an important part of the diagnostic process. A chest X-ray is one of the first tests performed and may show diffuse hazy areas, called infiltrates, across the lung fields, while a computed tomography (CT) scan of the chest can provide a more detailed view, often revealing widespread, patchy ground-glass opacities characteristic of blood in the air sacs.
Bronchoscopy with bronchoalveolar lavage (BAL) is often used to confirm active bleeding. During this procedure, a thin, flexible tube with a camera is guided into the lungs. A small amount of sterile saline is washed over a section of the lung and then collected for analysis, and an increasing amount of blood in sequential samples confirms the bleeding originates deep within the lungs.
A complete blood count (CBC) confirms anemia by measuring low hemoglobin and hematocrit levels resulting from blood loss. Blood tests are also analyzed for specific autoantibodies, such as antineutrophil cytoplasmic antibodies (ANCA) or anti-glomerular basement membrane (anti-GBM) antibodies, which can help identify an underlying autoimmune disease like vasculitis or Goodpasture syndrome.
Medical Interventions and Management
The immediate priority in managing DAH is stabilizing the patient’s respiratory function while the underlying cause is investigated. Many patients require supplemental oxygen, and in cases of severe respiratory distress, mechanical ventilation may be necessary to support breathing.
If an autoimmune disorder is responsible, the primary treatment involves medications to suppress the overactive immune system. High-dose corticosteroids, such as intravenous methylprednisolone, are administered to quickly reduce inflammation in the lung’s blood vessels. Other immunosuppressive drugs, like cyclophosphamide, may also be used for long-term control.
For certain autoimmune conditions, such as Goodpasture syndrome, a procedure called plasmapheresis may be employed. This process involves removing the patient’s blood, separating the plasma which contains the harmful antibodies, and replacing it with a substitute fluid, which helps eliminate the antibodies attacking the lung and kidney tissues.
When a specific medication is identified as the trigger, it is discontinued immediately. If an infection is the root cause, appropriate antimicrobial therapy is administered. In cases related to heart conditions, management would focus on treating the underlying cardiac issue to reduce pressure in the pulmonary vessels.
Prognosis and Recovery Outlook
The outlook for an individual with DAH is highly variable and depends on the underlying cause. The severity of the hemorrhage and the speed of diagnosis and treatment also influence the outcome.
With prompt management, many individuals can recover from an episode of DAH. For example, when DAH is triggered by a medication, stopping the drug can lead to resolution. Treating an underlying autoimmune disease with immunosuppressive therapy can also stop the bleeding and allow the lungs to heal.
Despite treatment advances, DAH remains a serious, potentially life-threatening event. The mortality rate can be significant and varies widely depending on the cause, with some studies showing rates from under 10% to over 50%. Factors such as the need for mechanical ventilation or the presence of kidney failure can indicate a poorer prognosis. Some patients may experience recurrent episodes or develop long-term lung changes, such as pulmonary fibrosis.