Goodpasture Syndrome Workup

Diffuse alveolar hemorrhage represents a medical emergency, and clinicians must have an expedient approach to its identification.^[7] In the appropriate clinical setting (ie, alveolar hemorrhage and urinary findings suggestive of an acute glomerulonephritis), the detection of circulating anti–glomerular basement membrane (anti-GBM) antibodies allows the clinician to make a firm diagnosis of anti-GBM disease. This obviates lung or kidney biopsy.

When the diagnosis remains in doubt, renal biopsy is the best method for detecting anti-GBM antibodies in tissues. Patients in whom the diagnosis of diffuse alveolar hemorrhage remains uncertain should undergo diagnostic bronchoscopy.

Urinalysis and blood studies

Urinalysis findings are characteristic of acute glomerulonephritis, usually demonstrating low-grade proteinuria, gross or microscopic hematuria, and red blood cell casts.

On the complete blood cell count, anemia may be observed secondary to iron deficiency caused by intrapulmonary bleeding. Leukocytosis is commonly present.

Elevated blood urea nitrogen (BUN) and serum creatinine levels secondary to renal dysfunction may be present.

Elevation of the erythrocyte sedimentation rate (ESR) is commonly observed in patients with vasculitis, but it is uncommon in anti-GBM disease.

Serologic assays for anti-GBM antibodies are valuable for confirming the diagnosis and monitoring the adequacy of therapy. Radioimmunoassays or enzyme-linked immunosorbent assays (ELISAs) for anti-GBM antibodies are highly sensitive (>95%) and specific (>97%) but are performed in only a few laboratories. Positive results should be confirmed by Western blotting on collagenase-solubilized human GBM, especially if a kidney biopsy is not being performed.

Although the peak of serum anti-GBM antibody titer does not correlate with the severity of disease, changes in titers over time may be a guide to the efficacy of therapy. IgG subclass distribution of anti-GBM antibodies may correlate with disease severity, however.^[8]

In a comparison study of 4 immunoassay-based anti-GBM antibody kits, all the assays showed comparably good sensitivity (94.7-100.0%), whereas specificity varied considerably (90.9-100.0%). The recombinant antigen fluorescence immunoassay demonstrated the best sensitivity/specificity.^[9]

A study by Yang et al indicated that high levels of circulating anti-GBM antibodies against the epitopes EA and EB may occur in patients whose renal disease is more severe and that these patients have a worse prognosis than patients with lower levels of these antibodies.^[10]

At some time during the course of illness, as many as one third of patients with Goodpasture syndrome have circulating antineutrophilic cytoplasmic antibodies (ANCAs) in addition to anti-GBM antibody.

Cytoplasmic ANCA (c-ANCA) and perinuclear ANCA (p-ANCA), seen in the images below, are prevalent equally.

In a substantial proportion of patients with crescentic glomerulonephritis (CGN), both anti-GBM antibodies and antineutrophil cytoplasmic antibodies (ANCAs) with specificity for myeloperoxidase (MPO-ANCA) are detected.^[11] In patients with both anti-GBM antibodies and MPO-ANCAs, histological findings differ from those of patients with anti-GBM antibodies only. The renal survival in these patients is similar to anti-GBM–positive patients and is worse compared with patients with MPO-ANCAs only.

Characteristically, the chest film shows patchy parenchymal consolidations, which are usually bilateral, symmetric perihilar, and bibasilar. The apices and costophrenic angles are usually spared (see the image below). However, as many as 18% of patients may have normal findings on chest radiographs.

The consolidation resolves over 2-3 days, and it gradually progresses to an interstitial pattern as patients experience repeated episodes of hemorrhage. Pleural effusions are unusual.

Routine pulmonary function testing is not helpful in the clinical evaluation of the patients with anti-GBM disease. Spirometry and lung volume tests may reveal evidence of restriction.

The diffusing capacity for carbon monoxide (DLCO) is elevated secondary to binding of carbon monoxide to intra-alveolar hemoglobin. Recurrent pulmonary hemorrhage may be diagnosed with new opacities observed on chest radiographs and a 30% rise in DLCO.

In patients with evidence of diffuse alveolar hemorrhage and renal involvement, kidney biopsy should be considered to identify the underlying cause and to help direct therapy. Percutaneous kidney biopsy is the preferred invasive procedure to substantiate the diagnosis of anti-GBM disease. Renal biopsy provides a significantly higher yield than lung biopsy, but transbronchial or open lung biopsy may be performed in cases where renal biopsy cannot be performed.

The biopsy tissue must be processed for light microscopy, immunofluorescence, and electron microscopy. Light microscopy demonstrates nonspecific features of a proliferative or necrotizing glomerulonephritis with cellular crescents (as seen in the image below). Over time, the crescents may fibrose, and frank glomerulosclerosis, interstitial fibrosis, and tubular atrophy may be observed.

Immunofluorescence stains are confirmatory. These show bright linear deposits of immunoglobulin G (IgG), as seen in the image below, and complement (C3) along the glomerular basement membranes. Subclass IgG-1 predominates.^[8]

Lung biopsy shows extensive hemorrhage with accumulation of hemosiderin-laden macrophages within alveolar spaces. Neutrophilic capillaritis, hyaline membranes, and diffuse alveolar damage may also be found. Medium-vessel or large-vessel vasculitis is not a feature.^[12] Immunofluorescence staining may be diagnostic, but performing this study on lung tissue is technically difficult.