| A 12 year old girl presents
with fever, rash, headache, weight loss and fatigue. Her knees,
ankles, elbows, and wrists showed warmth, swelling, redness, and
tenderness. Firm, painless nodules on the extensor surfaces of the
wrists, elbows, and knees were noticed. She displayed rapid,
purposeless movements of the face and upper extremities. It was
revealed that she had suffered from pharyngitis three weeks
earlier and had a history of repeated attacks of sore throat.
What is your diagnosis?
It is a case of acute rheumatic fever.
How do you diagnose this condition?
Clinically, diagnosis of acute rheumatic fever is made according
to revised Jones criteria by looking for major and minor criteria.
Either two major criteria or one major criterion and two minor
criteria along with history of strepotococcal throat infection is
required to establish rheumatic fever.
What is the pathogenesis of ARF?
Recurrent attacks of pharyngitis by Group A Streptococci may
lead to ARF. Some degree of antigenic cross-reactions is known to
occur between human antigens and streptococcal antigens. There is
similarity between group specific carbohydrate antigen of
Streptococcus pyogenes and the glycoprotein of the heart valves. An immune
response against the bacterial antigens is thought to mediate an
attack on cross-reacting self-antigens. Some amount of genetic
predisposition is also known to occur in such patients. Although
rheumatic fever is known to follow attacks of pharyngitis, few cases of rheumatic fever has been documented to occur following
streptococcal pyoderma in Australia. The exact mechanism of
pathogenesis is still not convincingly clear, but the evidences
suggest autoimmune phenomenon. Certain rheumatogenic strains belonging to M serotypes 1, 3, 5, 6 and 18
are frequently associated with ARF. These strains are known to
produce large amounts of M protein and possess hyaluronic acid
capsule.
How is the diagnosis of ARF made with laboratory tests?
A culture from throat swab is not useful as this condition
sets in after an episode of pharyngitis, however Group A
Streptococcus have been recovered from throat specimens. If
cultures are negative, streptococcal antigen detection by enzyme
immunoassay or latex agglutination can be attempted on throat
specimens. A retrospective diagnosis
can be made serologically by detecting anti-streptolysin O
antibodies in patient's serum. The ASO test that is frequently
used is based on latex agglutination. A titre of 200 units or
higher is considered significant. Additionally anti-DNase B or
anti-hyaluronidase too can be performed. A rise in antibody titre
from acute to convalescent stage is more reliable.
Why is anti-streptolysin S not used?
Streptolysin S is not antigenic; hence there are no anti-streptolysin
S antibodies.
How can the onset of ARF be prevented?
It can be prevented by treating patients with antibiotic (e.g.,Penicillin)
within nine days of onset of Streptococcal pharyngitis.
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