What are the differential diagnoses and recommended work‑up for a tender, swollen right post‑auricular lymph node?

Differential Diagnosis and Work-Up for Tender, Swollen Right Post-Auricular Lymph Node

Most Likely Diagnosis: Regional Lymphadenitis Secondary to Otitis Externa or Scalp Infection

A tender, swollen post-auricular lymph node in the absence of systemic symptoms most commonly represents reactive lymphadenopathy from acute otitis externa or a scalp infection (folliculitis, cellulitis) draining to the regional nodes. 1

Immediate Physical Examination Priorities

• Perform tragal tenderness test – press on the tragus or pull the pinna; intense tenderness is pathognomonic for acute otitis externa and confirms the ear canal as the infection source 2, 3
• Inspect the external auditory canal for edema, erythema, debris, or purulent discharge characteristic of otitis externa 2, 3
• Examine the scalp and post-auricular skin for folliculitis, cellulitis, ulcerations, or recent trauma/piercings that could serve as the primary infection source 4, 1
• Assess tympanic membrane integrity via otoscopy to guide topical antimicrobial selection 2, 3
• Palpate the lymph node to document size, tenderness, mobility, and consistency – tender, mobile nodes favor reactive lymphadenitis over malignancy 1

First-Line Management When Otitis Externa is Confirmed

Topical fluoroquinolone ear drops (ofloxacin 0.3% or ciprofloxacin 0.2%) are the definitive first-line treatment; oral antibiotics are NOT indicated for uncomplicated cases. 2 The presence of ipsilateral lymphadenopathy alone does not warrant systemic antibiotics when infection remains confined to the ear canal. 2

• Before applying any drops, perform aural toilet – remove debris, cerumen, and inflammatory material via gentle suction or dry mopping to ensure medication reaches infected tissue 2
• Prescribe topical drops for minimum 7 days even if symptoms resolve earlier 2
• Provide aggressive analgesia – acetaminophen or NSAIDs for mild-to-moderate pain; short-term opioids for severe pain during the first 48–72 hours 2, 3
• Expect pain and lymph node tenderness to improve within 48–72 hours of starting appropriate therapy 2

Indications to Add Systemic Antibiotics (Oral Fluoroquinolones)

Systemic therapy is reserved for specific high-risk situations: 2

• Extension of infection beyond the ear canal (periauricular cellulitis or swelling)
• Diabetes mellitus or immunocompromised status
• Severe canal edema preventing adequate topical drug delivery despite wick placement
• Lack of clinical improvement (including persistent lymphadenopathy) after 48–72 hours of appropriate topical therapy

When systemic antibiotics are indicated, prescribe ciprofloxacin 500 mg twice daily to cover Pseudomonas aeruginosa and Staphylococcus aureus, which cause ~98% of otitis externa cases. 2

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Alternative Diagnosis: Scalp Infection

If otoscopy is normal and tragal tenderness is absent, examine the scalp meticulously for folliculitis or cellulitis – these infections drain to post-auricular nodes and represent common benign causes of regional lymphadenopathy. 1 Treat the primary scalp infection with appropriate topical or oral antibiotics targeting Staphylococcus aureus.

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Red Flags Requiring Urgent Evaluation for Malignancy or Mycobacterial Infection

When to Suspect Malignancy (Requires CT Neck with Contrast and ENT Referral)

Any of the following features mandate comprehensive evaluation: 1

• Node present ≥2 weeks without fluctuation
• Firm or hard consistency
• Size >1.5 cm
• Fixation to adjacent tissues or overlying skin ulceration
• Age >40 years with tobacco/alcohol use
• Associated hoarseness, dysphagia, odynophagia, or unexplained weight loss

When to Suspect Nontuberculous Mycobacterial (NTM) Lymphadenitis

In children aged 1–5 years, unilateral, non-tender, insidious lymph node enlargement suggests NTM infection. 4, 1 In adults, >90% of culture-proven mycobacterial lymphadenitis is M. tuberculosis, requiring drug therapy and public health tracking. 4, 1

• Definitive diagnosis requires excisional biopsy – fine needle aspiration or incision and drainage alone leads to fistula formation and chronic drainage 4, 1
• Tuberculin skin testing should be performed in all patients with suspected mycobacterial lymphadenitis 4
• Chest radiograph is mandatory to exclude pulmonary tuberculosis 4

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Critical Pitfalls to Avoid

• Never prescribe oral antibiotics for uncomplicated otitis externa – topical therapy achieves 77–96% cure rates versus 30–67% for oral regimens, yet 20–40% of patients inappropriately receive systemic antibiotics 2
• Never perform incision and drainage for suspected NTM lymphadenitis – this leads to fistula formation and chronic drainage; complete excisional biopsy is required 4, 1
• Never assume cystic masses are benign – cystic metastases are common in head and neck cancers 1
• Avoid empiric antibiotics without clear infectious signs – most adult neck masses are neoplastic, not infectious 1

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Reassessment and Follow-Up

• Reassess within 48–72 hours if symptoms do not improve with topical therapy 2
• Long-term stability (years without change) definitively excludes malignancy – benign lymph nodes can persist indefinitely after resolving infections 1
• If the node persists beyond 2 weeks or enlarges despite appropriate treatment, obtain CT neck with contrast to evaluate for occult malignancy or atypical infection 1