How do you clinically diagnose mastoiditis (inflammation of the mastoid bone) versus Acute Otitis Media (AOM, middle ear infection)?

Clinical Diagnosis of Mastoiditis versus Acute Otitis Media

The key clinical distinction between mastoiditis and acute otitis media (AOM) is the presence of mastoid tenderness, retroauricular swelling, and protrusion of the auricle in mastoiditis, which are not present in uncomplicated AOM. 1

Diagnostic Features of Acute Otitis Media

Clinical Presentation

• AOM typically presents with ear pain (otalgia), fever, and irritability 1
• Hearing problems are common (67%) but retroauricular symptoms are uncommon in AOM 2
• Symptoms may include ear tugging, decreased appetite, and sleep disturbance 1

Otoscopic Findings

• Bulging tympanic membrane (TM) is the most reliable sign of AOM 1
• Intense erythema of the TM is often present 1
• Middle ear effusion (MEE) is present, indicated by limited or absent TM mobility 1
• Otorrhea may be present if the TM has ruptured 1

Diagnostic Features of Mastoiditis

Clinical Presentation

• Mastoiditis presents with mastoid tenderness (65% of cases) 2
• Retroauricular swelling and erythema (74-95% of cases) 3, 4
• Protrusion/proptosis of the auricle (58-91% of cases) 3, 4
• Fever is common (44-75% of cases) 3, 2
• Mastoiditis often follows AOM, but can occur in 45-46% of patients with no prior history of AOM 4, 2

Otoscopic Findings

• Similar TM findings to AOM (bulging, erythema) 1
• Sagging of the posterior superior wall of the external auditory canal may be present 5
• Otorrhea is common, especially in cases with Pseudomonas aeruginosa (94%) 2

Key Differential Diagnostic Points

• Retroauricular signs: Mastoiditis shows swelling, erythema, and tenderness over the mastoid process, which are absent in uncomplicated AOM 1, 3
• Auricle displacement: Protrusion of the auricle away from the head is characteristic of mastoiditis but not seen in AOM 4
• Systemic symptoms: Mastoiditis typically presents with more severe systemic symptoms including higher fever and elevated inflammatory markers 6
• Treatment response: Failure to improve after 48 hours of appropriate antibiotic therapy for AOM should raise suspicion for mastoiditis 7, 5

When to Suspect Complications of AOM

• Persistent fever >39°C (102.2°F) despite 48 hours of antibiotic therapy 1
• Worsening symptoms after initial improvement 7
• Development of retroauricular swelling, erythema, or tenderness 1
• Neurological symptoms (headache, vertigo, meningismus, neck rigidity) 1
• Facial nerve paralysis 3

Diagnostic Algorithm

1. Initial assessment: Evaluate for ear pain, fever, and otoscopic findings of AOM (bulging TM, erythema) 1

2. Examine mastoid area: Check for:

   • Tenderness over the mastoid process 2
   • Retroauricular swelling or erythema 3
   • Protrusion of the auricle 4

3. Decision point:

   • If only ear pain and otoscopic findings of AOM without mastoid signs → Diagnose AOM 1
   • If mastoid tenderness, swelling, or auricle protrusion present → Suspect mastoiditis 1, 3

4. For suspected mastoiditis:

   • Obtain imaging (CT temporal bone) to confirm diagnosis 1, 5
   • Evaluate for potential complications 1
   • Initiate prompt treatment with IV antibiotics 7

Common Pitfalls and Caveats

• Mastoiditis can develop despite prior antibiotic treatment for AOM (33-81% of mastoiditis cases had received antibiotics previously) 7
• Relying solely on otoscopic findings may miss mastoiditis; always examine the mastoid area in cases of severe or persistent AOM 1
• Cultures from mastoid infections may be negative in up to 33-53% of cases, emphasizing the importance of clinical diagnosis 7
• The absence of prior AOM does not rule out mastoiditis, as 45-46% of mastoiditis cases occur without prior AOM history 4
• While CT imaging is definitive for diagnosing mastoiditis, the initial clinical diagnosis should be made based on physical examination findings 1, 5