Question
A six-year-old boy presented with history of dysphagia, fever and throat pain for the last 3 days. On examination, his throat was congested and tender lymphadenopathy in the cervical area was noted.
- (a) What is the most probable diagnosis 2 mark(s)
- (b) Describe the pathogenesis of this disease 3 mark(s)
- (c) Name two non-suppurative sequelae 2 mark(s)
- (d) How will you confirm the diagnosis 3 mark(s)
Answer
a) Most probable diagnosis: Streptococcal pharyngitis (acute tonsillopharyngitis caused by Streptococcus pyogenes, Group A Streptococcus) — fever, sore throat/dysphagia, congested throat, and tender cervical lymphadenopathy in a child is classical.
b) Pathogenesis S. pyogenes adheres to pharyngeal epithelium via M protein and lipoteichoic acid, colonizing the mucosa and provoking a local acute inflammatory response (congestion, exudate, tonsillar enlargement). The organism elaborates several virulence factors: streptolysin O and S (haemolysins, cytotoxic to host cells), streptokinase (promotes spread by dissolving fibrin), hyaluronidase (“spreading factor”), and pyrogenic exotoxins (in strains causing scarlet fever). Local spread can extend to cervical lymph nodes (producing the tender lymphadenopathy) or, if untreated, to deeper tissues (peritonsillar abscess). Distinctively, S. pyogenes also triggers immune-mediated (non-suppurative) complications weeks after the acute infection, via molecular mimicry and immune-complex deposition, rather than by direct bacterial invasion of the affected organ.
c) Two non-suppurative sequelae
- Acute rheumatic fever — 2–4 weeks after pharyngitis, due to molecular mimicry between streptococcal M protein and cardiac tissue, causing carditis, migratory polyarthritis, and other Jones-criteria features.
- Acute post-streptococcal glomerulonephritis (PSGN) — 1–3 weeks after pharyngitis, due to immune-complex deposition in the glomerular basement membrane, causing haematuria, oedema, and hypertension.
d) Confirmation of diagnosis
- Throat swab culture — beta-haemolytic colonies on blood agar; bacitracin-sensitive (distinguishing Group A from other beta-haemolytic streptococci); Lancefield Group A carbohydrate antigen confirmation.
- Rapid antigen detection test (RADT) — detects Group A streptococcal antigen directly from a throat swab, providing rapid point-of-care results, though less sensitive than culture (a negative RADT in a clinically suspicious case should be confirmed by culture).
- ASO (antistreptolysin O) titre — rises 1–3 weeks after infection; more useful for retrospectively confirming a recent streptococcal infection (e.g., when investigating suspected rheumatic fever) than for diagnosing the acute pharyngitis itself.