Diagnosis of Rheumatic Fever
The diagnosis of rheumatic fever is always made based on a number of criteria. There is no single study or test which can be made to diagnose rheumatic fever right away.
The physical examination includes the following points:
- Checking the body temperature of the patient;
- Checking for signs of arthritis;
- Examining the skin for rash and subcutaneous nodules;
- Using a stethoscope to discover heart murmurs, muffled sounds, and arrhythmias;
- Asking the patient to perform a series of movement tests which can indirectly provide evidence of inflammation of the central nervous system.
To identify if the person has streptococcal infection and make a diagnosis (unless the person already has chorea or indolent rheumatic heart disease) the following must be done:
- Throat culture is the standard procedure to confirm group A streptococcal infection.
- Rapid antigen detection test is a quicker method of detecting streptococcal infection; however, it is not as sensitive as culture.
o If the tests for rapid antigen detection test are negative, a throat culture must still be obtained in order to exclude the possibility of streptococcal infection.
o However, if the test is positive, it confirms streptococcal infection, due to its high specificity.
Another method of detecting a streptococcal infection is by measuring the anti-streptococcal antibody titre levels at certain intervals to see if the antibody titre levels will grow. If the titre of antibodies is elevated but does not grow, this means that the person had a streptococcal infection some time in the past.
- Anti-streptolysin O (ASO) test – this test can detect antibodies that target streptococcal lysin O. Elevated titre of ASO is a proof of previous streptococcal infection. Pharyngeal infection usually raises ASO titre a lot more than skin infection.
Antibody titre tests should be interpreted with caution, especially in the areas where streptococcal infection is common. These tests provide more insight in places where a streptococcal infection is encountered much more rarely (e.g. most Western countries).
C-reactive protein levels, erythrocyte sedimentation rate, and acute-phase reactants are usually raised right from the beginning of acute rheumatic fever. Even though these tests are nonspecific, they provide means of monitoring the activity of the disease.
Blood cultures should also be obtained to rule out bacteremia and the possibility of infective endocarditis.
Chest radiography (X-ray) – can be used to detect cardiomegaly caused by carditis associated with rheumatic fever.
Echocardiography is used to detect valvular regurgitant lesions in people with acute rheumatic fever, although they might not have clinical manifestations of carditis (subclinical carditis). Even if the regurgitant lesions are detected using echocardiography, they do not qualify as carditis and used as a diagnostic criterion. Some scientists believe that this should be changed, since in Australia and New Zealand for example, echocardiography can be used to prove carditis. This allows for the detection of 16-47% more cases of carditis.
Echocardiography can also be used to detect valvular stenotic lesions caused by rheumatic heart disease.
It should be noted that it is uncommon for rheumatic heart disease to affect the aortic valve without affecting the mitral valve.
- Electrocardiography (ECG). Prolongation of PR interval is the most common finding on ECG in patients with rheumatic fever. Although it is a nonspecific finding, it counts as minor criterion during diagnosis. Moreover, it cannot be used as a proof of carditis.
o In rarer cases the patient may have second or third-degree heart blocks.
o In some patients the ECG may show enlargement of the left atrium which resulted from mitral stenosis.
- Other tests are usually used for differential diagnosis and include antinuclear antibody, rheumatoid factor, Lyme serology, evaluation for gonorrhea, and blood cultures.
Next Chapter: Treatment of Rheumatic fever