How do you diagnose a peritonsillar infection?

Diagnosis of Peritonsillar Infection

The diagnosis of peritonsillar infection requires a combination of clinical evaluation, laboratory tests, and imaging, with needle aspiration remaining the gold standard for confirming a peritonsillar abscess and distinguishing it from peritonsillar cellulitis. 1

Clinical Presentation

Key Symptoms and Signs

• Throat pain (74-95% of cases) 2
• Fever (38% of cases) 2
• Trismus (difficulty opening mouth) - statistically associated with abscess 3
• "Hot potato" voice 4
• Dysphagia 4
• Uvular deviation toward the unaffected side - statistically associated with abscess 3
• Anterior pillar bulging - statistically associated with abscess 3

Physical Examination

• Inspect for asymmetry of the tonsillar area
• Look for bulging of the affected tonsil
• Check for deviation of the uvula away from the affected side
• Assess degree of trismus (limited mouth opening)
• Examine for fluctuance of the peritonsillar area when safe to do so

Diagnostic Approach

Step 1: Initial Assessment

• Clinical evaluation alone has limited reliability (sensitivity 78%, specificity 50%) 5
• Laboratory tests should include:
  • Complete blood count (leukocytosis is present in 40% of cases) 2
  • C-reactive protein 2

Step 2: Diagnostic Imaging

When diagnosis is uncertain based on clinical presentation alone:

• Intraoral ultrasound is highly accurate (sensitivity 89%, specificity 100%) 5 and should be considered first-line when available
• CT scan with contrast is also highly accurate (sensitivity 100%, specificity 75%) 5 and is the imaging modality of choice for adults when complications or deep space extension is suspected 2

Step 3: Diagnostic Aspiration

• Needle aspiration remains the gold standard for diagnosis 1, 3
• Procedure:
  • Use a large gauge needle (18-20G)
  • Direct the needle to the point of maximum fluctuance
  • Aspirate to obtain purulent material
  • Positive aspiration confirms abscess
  • Negative aspiration suggests peritonsillar cellulitis

Differential Diagnosis

• Peritonsillar cellulitis (no discrete collection of pus)
• Retropharyngeal abscess
• Parapharyngeal abscess
• Epiglottitis
• Infectious mononucleosis
• Ludwig's angina
• Dental abscess

Pitfalls and Caveats

• Clinical examination alone is insufficient for distinguishing between peritonsillar abscess and cellulitis 5
• Beware of atypical presentations in immunocompromised patients or those with altered mental status 6
• Avoid blind incision and drainage without first confirming the presence and location of an abscess
• Consider that 77% of patients with peritonsillar infection have no history of recurrent tonsillitis 3
• Be aware that 55% of patients may already be on antibiotics at presentation 3

Management Considerations

Once diagnosed, treatment typically includes:

• Drainage of the abscess (needle aspiration, incision and drainage, or tonsillectomy)
• Antibiotic therapy effective against Group A Streptococcus and oral anaerobes
• Pain control and hydration support
• Most patients can be managed as outpatients 4

Early diagnosis and appropriate treatment are crucial to prevent complications such as airway obstruction, aspiration, or extension of infection into deep neck tissues 4.