November 29, 2010

USMLE 2 Question 22

A 35 year old has severe hemoptysis three weeks following a respiratory tract infection. Investigations reveal pulmonary infiltrates suggestive of alveolar hemorrhage. She is found to have hypertension, generalised edema. Urinalysis reveals hematuria and red cell casts. Her renal function is reduced. Serologic tests for ANA and rheumatoid factor are negative. Circulating antibodies to the glomerular basement memebrane are discovered.

A likely diagnosis is:

a) polycystic disease of the kidneys
b) Berger's nephritis
c) systemic lupus erythematosus
d) renal vein thrombosis
e) Goodpasture's syndrome








ANSWER
The correct answer is E



Explanation
The diagnosis of anti-GBM antibody disease depends on the demonstration of circulating anti-GBM antibodies and/or the finding of linear deposits of immunoglobulin along glomerular or alveolar basement membranes. In the appropriate clinical setting (alveolar hemorrhage and urinary findings suggestive of active glomerulonephritis), a positive test for circulating anti-GBM antibodies establishes the diagnosis and obviates the need for further diagnostic testing.

True Goodpasture syndrome should consist of the following triad: 1) proliferative, usually crescentic, glomerulonephritis; 2) pulmonary hemorrhage; and 3) the presence of anti-GBM antibodies. When present, the renal disease may be severe and follow a fulminant course, progressing to renal failure over hours to weeks if untreated.

Approximately 20% of patients presenting with rapidly progressive glomerulonephritis will have anti-GBM antibody disease with or without lung hemorrhage. In anti-GBM antibody disease, the pulmonary hemorrhage may precede, occur concurrently with, or follow the glomerular involvement. Documentation of anti-GBM antibody-induced disease may be accomplished by renal biopsy, or by establishing the presence of circulating anti-GBM antibodies. Radioimmunoassay, ELISA, and immunoblotting for the antibodies are both highly specific and sensitive.

Glomerulonephritis The majority of cases of anti-GBM antibody disease occur in the second through the fifth decade of life, although cases have been diagnosed late in life. An upper respiratory tract infection precedes the onset of disease in 20% to 60% of cases. The most common extrarenal findings are by far related to pulmonary involvement. Patients may have cough, dyspnea, and shortness of breath, and hemoptysis may vary from trivial amounts to life-threatening massive amounts associated with exsanguination and suffocation.

In almost three fourths of cases, pulmonary hemorrhage precedes or is coincident with the glomerular disease. Hemoptysis will occur in virtually all patients with pulmonary and renal disease at some point during the course of their illness and will be the presenting symptom in a majority of individuals. Symptoms referable to the renal disease usually are nonspecific and are related to hematuria or to the degree of azotemia.

The clinical renal presentation may be with an acute nephritic picture with hypertension, edema, hematuria and active urinary sediment, and reduced renal function. Laboratory evaluation in patients with Goodpasture syndrome typically shows active urinary sediment with red blood cells and red cell casts on urinalysis. Proteinuria, although commonly present, is usually not in the nephrotic range, perhaps secondary to the reduction in GFR commonly present. Serologic tests such as ASLO, ANA, serum complement levels, rheumatoid factor, cryoglobulins, and CICs are all either negative or normal. Circulating anti-GBM antibodies are present in over 90% of patients.

In patients with pulmonary involvement, the chest x-ray results are abnormal in over 75% and typically show infiltrates corresponding to areas of pulmonary hemorrhage. Approximately 60% to 80% of patients with anti-GBM antibody disease will have clinically apparent pulmonary and renal disease, whereas some 20% to 40% will have glomerulonephritis alone, and 10% or less will have isolated pulmonary disease.

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