Pharyngitis & Tonsillitis
A Step 2 CK high-yield lesson on pharyngitis and tonsillitis centered on identifying Group A Strep with the Centor/McIsaac score and RADT, first-line penicillin/amoxicillin, and the classic board vignettes (peritonsillar abscess, EBV mono with the amoxicillin rash) plus suppurative and non-suppurative complications.
Overview: the one decision that matters
Pharyngitis is inflammation of the pharynx and tonsils, and most cases are viral and self-limited (rhinovirus, adenovirus, coronavirus, influenza; EBV in young adults). The board-relevant task is identifying Group A Streptococcus (GAS, Streptococcus pyogenes) — the only common cause routinely treated — because antibiotics prevent acute rheumatic fever, shorten symptoms, cut transmission, and reduce suppurative complications.
Viral clues: cough, coryza, conjunctivitis, hoarseness, oral ulcers, diarrhea. GAS clues: sudden sore throat, fever, tonsillar exudates, tender anterior cervical nodes, palatal petechiae, absence of cough/URI symptoms, peak age 5–15, winter/spring.
Don't test or treat when the picture is clearly viral. When features overlap, use the Centor/McIsaac score to decide whom to test.
- Most common cause = viral → supportive care only (no antibiotics)
- GAS = the cause to catch; peak age 5–15; prevents rheumatic fever
- Modified Centor (McIsaac) +1 each: tonsillar exudate, tender anterior cervical nodes, fever >38°C, no cough; age 3–14 (+1), 15–44 (0), ≥45 (−1)
- Score ≤1 → no test, no antibiotics; 2–3 → RADT, treat if positive; ≥4 → RADT/culture, treat if positive (no empiric treatment)
- RADT = high specificity; a negative RADT in a child must be confirmed by throat culture (lower sensitivity). Adults do NOT need a backup culture
- First-line: penicillin V or amoxicillin ×10 days; single IM benzathine penicillin G if adherence is a concern
- Penicillin allergy: cephalexin (non-anaphylactic), azithromycin, or clindamycin
- Antibiotics prevent rheumatic fever (if started within ~9 days of onset) but do NOT prevent post-streptococcal glomerulonephritis
Viral vs GAS vs EBV mononucleosis
| Feature | Viral | GAS (strep) | EBV mono |
|---|---|---|---|
| Age | Any | 5–15 | Teens / young adults |
| Cough & coryza | Present | Absent | Absent |
| Exudate | ± | Yes | Yes (can be grey) |
| Lymph nodes | Anterior, mild | Tender anterior | Posterior + diffuse |
| Spleen | No | No | Splenomegaly |
| Extra clue | Ulcers, conjunctivitis | Palatal petechiae, scarlatiniform rash | Rash after amoxicillin, fatigue |
| Test | None | RADT ± culture | Heterophile (Monospot), atypical lymphocytes |
| Treatment | Supportive | Penicillin/amoxicillin | Supportive; avoid contact sports |
An 8-year-old has 2 days of sudden sore throat and fever to 38.9°C, no cough or rhinorrhea. Exam shows tonsillar exudates, tender anterior cervical nodes, and palatal petechiae.
Score: all 4 Centor features + age 3–14 → McIsaac 5.
Next best step: rapid antigen detection test (RADT). If positive → penicillin V or amoxicillin ×10 days. If the RADT is negative in this child, send a throat culture before withholding antibiotics (pediatric RADT can miss cases and untreated GAS risks rheumatic fever).
Trap: do not order ASO titers acutely — they rise late and are for confirming prior infection (rheumatic fever/PSGN workup), not acute diagnosis.
A 19-year-old has several days of worsening unilateral sore throat, now with muffled "hot potato" voice, trismus (can't fully open the mouth), drooling, and fever. Exam shows a bulging peritonsillar swelling with the uvula deviated to the opposite (contralateral) side.
Diagnosis: peritonsillar abscess — the most common deep neck space infection in adolescents/young adults; usually polymicrobial (strep + oral anaerobes).
Next best step: needle aspiration or incision and drainage plus antibiotics covering strep and anaerobes (e.g., amoxicillin-clavulanate or clindamycin). Get a CT neck with contrast only if the diagnosis is unclear or extension into deeper spaces is suspected. Consider tonsillectomy for recurrent PTA.
A 20-year-old college student has a week of fatigue and sore throat, was given amoxicillin for presumed strep, and now develops a diffuse maculopapular rash. Exam: exudative tonsillitis, posterior cervical lymphadenopathy, and splenomegaly; smear shows atypical lymphocytes.
Diagnosis: infectious mononucleosis (EBV). The ampicillin/amoxicillin rash is a classic buzzword — it is NOT a true penicillin allergy.
Diagnosis/next step: heterophile (Monospot) antibodies; if negative in the first week, it can be falsely negative → repeat or order EBV-specific serologies (VCA IgM).
Management: supportive care; avoid contact sports ≥3–4 weeks due to risk of splenic rupture. Corticosteroids only for airway obstruction from tonsillar swelling.
The Centor/McIsaac score is eponymous (Dr. Robert Centor), but the letters double as a handy memory aid for GAS probability:
- C — Cough absent (+1)
- E — Exudate on tonsils (+1)
- N — Nodes: tender anterior cervical (+1)
- T — Temperature >38°C / fever (+1)
- OR — age modifier: 3–14 (+1), 15–44 (0), ≥45 (−1)
Higher score → higher GAS likelihood → test (RADT). Score ≤1 needs neither testing nor antibiotics. The score guides who to test, not automatic empiric antibiotics.
Suppurative (spread of infection):
- Peritonsillar abscess, retropharyngeal abscess, otitis media, sinusitis, cervical lymphadenitis
- Lemierre syndrome: Fusobacterium necrophorum → septic internal jugular vein thrombophlebitis with septic pulmonary emboli in a young adult with persistent pharyngitis
Non-suppurative sequelae (immune-mediated):
- Acute rheumatic fever — molecular mimicry; prevented by timely antibiotics
- Post-streptococcal glomerulonephritis — immune-complex mediated; NOT prevented by antibiotics
- PANDAS — proposed post-streptococcal autoimmune neuropsychiatric syndrome
Toxin-mediated: scarlet fever (erythrogenic exotoxin) — sandpaper rash, strawberry tongue, circumoral pallor.
Retropharyngeal abscess: young child, neck stiffness/hyperextension, drooling; lateral neck film shows widened prevertebral soft tissue; risk of mediastinitis.
Tonsillectomy (Paradise) criteria: ≥7 episodes in 1 yr, ≥5/yr for 2 yr, or ≥3/yr for 3 yr; also recurrent PTA or obstructive sleep apnea.
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