Diffuse alveolar hemorrhage (DAH) is a serious medical syndrome involving acute, widespread bleeding within the lungs. This condition occurs when blood leaks from the tiny blood vessels of the lung tissue and floods the air sacs, or alveoli. DAH is considered an emergency because the presence of blood directly interferes with the body’s ability to take in oxygen, often leading to sudden respiratory failure.
Defining Diffuse Alveolar Hemorrhage
The function of the lungs relies on millions of microscopic air sacs called alveoli, which are surrounded by a fine mesh of capillaries. These capillaries form the delicate barrier where oxygen from inhaled air passes into the bloodstream and carbon dioxide moves out. Diffuse alveolar hemorrhage results from damage to this alveolar-capillary basement membrane, causing blood to escape from the pulmonary microvasculature into the air spaces.
The term “diffuse” indicates that this bleeding is not localized to one small area but is spread across both lungs, involving the lung parenchyma. When the alveoli fill with blood instead of air, impaired gas exchange rapidly leads to low oxygen levels in the blood. DAH is a syndrome, meaning it is a group of symptoms and findings caused by a variety of underlying disorders. Pathologically, DAH can manifest in three main ways: pulmonary capillaritis (inflammation of the vessel walls), bland pulmonary hemorrhage (bleeding without inflammation), or diffuse alveolar damage.
Underlying Causes and Risk Factors
The most frequent underlying causes of DAH are systemic autoimmune diseases, where the immune system mistakenly attacks its own tissues, including the small vessels in the lungs. One of the primary culprits is a group of conditions called systemic vasculitides, which involve inflammation of the blood vessel walls. For example, ANCA-associated vasculitis (including microscopic polyangiitis and granulomatosis with polyangiitis) often targets the lung capillaries, leading to capillaritis.
Another significant immune-mediated cause is Anti-Glomerular Basement Membrane (Anti-GBM) disease, sometimes known as Goodpasture syndrome, where antibodies specifically attack components of the alveolar and kidney basement membranes. Connective tissue diseases also commonly trigger DAH, most notably Systemic Lupus Erythematosus (SLE). In many of these cases, DAH is part of a pulmonary-renal syndrome, affecting both the lungs and the kidneys simultaneously.
Less common triggers include drug reactions, certain infections, and coagulation disorders. For instance, certain medications (such as antiplatelet therapies) or toxins like crack cocaine have been implicated as risk factors. Infectious causes, though rare in immunocompetent patients, can include severe influenza A (H1N1) or dengue fever, while immunocompromised individuals may develop DAH from infections like cytomegalovirus or invasive aspergillosis.
Recognizing the Signs
The presentation of DAH can vary widely, but patients frequently develop an acute onset of respiratory distress. The most recognizable sign is hemoptysis, which is coughing up blood, though this symptom is not always present and may be absent in up to one-third of patients. The blood can be internalized and not coughed up, making the diagnosis more challenging.
Patients experience acute shortness of breath (dyspnea), which can quickly progress to respiratory failure and require mechanical ventilation. Ongoing internal bleeding causes a rapid decrease in the red blood cell count, leading to anemia. This drop in hemoglobin may be one of the first clues supporting a diagnosis when external bleeding is not obvious. Non-specific symptoms, such as fever, cough, and general malaise, may precede the acute hemorrhage, especially when the cause is an underlying systemic illness.
Diagnostic Procedures
Confirming DAH requires a high index of suspicion based on the clinical presentation and initial imaging. Chest X-rays and Computed Tomography (CT) scans are typically obtained first and often show bilateral, diffuse areas of consolidation or ground-glass opacities, which represent blood filling the air spaces. These findings are suggestive but not definitive, as they can also be seen in other conditions like pneumonia.
The definitive procedure for diagnosing DAH is a bronchoscopy with bronchoalveolar lavage (BAL). A flexible tube is inserted into the airways, where saline solution is washed into a lung segment and then suctioned back out. The diagnostic finding is the presence of persistent or progressively increasing blood in the sequential fluid samples collected. Blood tests are also performed to search for specific autoantibodies, such as ANCA or anti-GBM antibodies, which help pinpoint the underlying autoimmune cause.
Treatment and Management Strategies
The management of DAH involves two parallel strategies: providing supportive care for acute respiratory failure and aggressively treating the underlying cause. Supportive measures are implemented immediately to stabilize the patient, often including supplemental oxygen and mechanical ventilation if severe respiratory distress is present. Blood transfusions may also be necessary to correct the acute anemia caused by the blood loss.
Treatment targeting the cause focuses overwhelmingly on suppressing the immune system, particularly when an autoimmune condition is identified. High-dose intravenous glucocorticoids, such as methylprednisolone, are the standard first-line therapy to rapidly control the inflammatory damage to the lung capillaries. These steroids are frequently combined with other potent immunosuppressive agents like cyclophosphamide or rituximab to achieve long-term control of the autoimmune process. In cases of Anti-GBM disease, plasma exchange is often added to the regimen to physically remove the harmful circulating antibodies from the blood.