In the absence of local or regional adenopathy, consider noninfectious causes of inflammation, among which trauma, insect bites, and environmental exposures are more commonly implicated than are autoimmune diseases (e.g., lupus) or vasculitides (e.g., granulomatosis with polyangiitis).

• Auricular cellulitis: Tenderness, erythema, swelling, and warmth of the external ear, particularly the lobule, follow minor trauma. Treat with warm compresses and antibiotics active against S. aureus and streptococci (e.g., cephalexin, dicloxacillin).
• Perichondritis: Infection of the perichondrium of the auricular cartilage follows local trauma (e.g., ear piercing). The infection may closely resemble auricular cellulitis, although the lobule is less often involved in perichondritis.
  • - Treatment requires systemic antibiotics active against the most common etiologic agents, Pseudomonas aeruginosa and S. aureus, and typically consists of an anti-pseudomonal penicillin (e.g., piperacillin) or a penicillinase-resistant penicillin (e.g., nafcillin) plus an antipseudomonal quinolone (e.g., ciprofloxacin). Surgical drainage may be needed; resolution can take weeks.
  • - If perichondritis fails to respond to adequate treatment, consider noninfectious inflammatory etiologies (e.g., relapsing polychondritis).
• Otitis externa: a collection of diseases involving primarily the auditory meatus and resulting from a combination of heat and retained moisture, with desquamation and maceration of the epithelium of the outer ear canal. All forms are predominantly bacterial in origin; P. aeruginosa and S. aureus are the most common pathogens.
  • - Acute localized otitis externa: furunculosis in the outer third of the ear canal, usually due to S. aureus. Treatment consists of an oral antistaphylococcal penicillin (e.g., dicloxacillin, cephalexin), with surgical drainage in cases of abscess formation.
  • - Acute diffuse otitis externa (swimmer's ear): infection in macerated, irritated canals that is typically due to P. aeruginosa and is characterized by severe pain, erythema, and swelling of the canal and white clumpy discharge from the ear. Treatment includes cleansing of the canal to remove debris and use of topical agents (e.g., hypertonic saline, mixtures of alcohol and acetic acid, antibiotic preparations combining neomycin and polymyxin), with or without glucocorticoids to reduce inflammation.
  • - Chronic otitis externa: erythematous, scaling, pruritic dermatitis that usually arises from persistent drainage from a chronic middle-ear infection, other causes of repeated irritation, or rare chronic infections such as tuberculosis or leprosy. Treatment consists of identifying and eliminating the offending process; successful resolution is frequently difficult.
  • - Malignant or necrotizing otitis externa: a slowly progressive infection characterized by purulent otorrhea, an erythematous swollen ear and external canal, and severe otalgia out of proportion to exam findings, with granulation tissue present in the posteroinferior wall of the canal, near the junction of bone and cartilage
    • This potentially life-threatening disease, which occurs primarily in elderly diabetic or immunocompromised pts, can involve the base of the skull, meninges, cranial nerves, and brain.
    • P. aeruginosa is the most common etiologic agent, but other gram-negative bacilli, S. aureus, Staphylococcus epidermidis, Actinomyces, and Aspergillus have been reported.
    • A biopsy specimen of granulation tissue (or deeper tissues) should be obtained for culture.
    • Treatment involves systemic antibiotics for 6-8 weeks and consists of antipseudomonal agents (e.g., piperacillin, ceftazidime) with an aminoglycoside or a fluoroquinolone; antibiotic drops active against Pseudomonas, combined with glucocorticoids, are used as adjunctive treatment.
    • Recurs in up to 20% of cases. Aggressive glycemic control in diabetic pts helps with treatment and prevention of recurrence.