Differential Diagnosis for Abscess Underarms

The following differential diagnosis is organized into categories to help guide the thought process:

• Single Most Likely Diagnosis
  • Folliculitis or Furuncle: This is the most common cause of an abscess in the underarm area, often resulting from bacterial infection (usually Staphylococcus aureus) of the hair follicles.
• Other Likely Diagnoses
  • Hidradenitis Suppurativa: A chronic skin condition characterized by recurrent, painful abscesses in areas of the body with apocrine sweat glands, such as the underarms.
  • Cutaneous Abscess: A localized collection of pus in the skin, which can occur in the underarm area due to bacterial infection.
  • Infected Epidermal Inclusion Cyst: These cysts can become infected and form an abscess, especially in areas prone to friction and moisture like the underarms.
• Do Not Miss Diagnoses
  • Cat-Scratch Disease: Although less common, this bacterial infection (Bartonella henselae) can cause lymphadenopathy and abscesses, particularly if the individual has been scratched by a cat.
  • Tuberculosis: While rare, cutaneous tuberculosis can manifest as abscesses or ulcers in the skin, including the underarm area, especially in immunocompromised individuals.
  • Actinomycosis: A rare bacterial infection that can cause abscesses, often in the face and neck but potentially in other areas, including the underarms, especially after trauma or surgery.
• Rare Diagnoses
  • Nocardiosis: A rare infection caused by Nocardia bacteria, which can lead to abscesses in the skin, including the underarm area, particularly in immunocompromised patients.
  • Mycobacterium Avium Complex (MAC) Infection: In immunocompromised individuals, MAC can cause a variety of infections, including skin abscesses.
  • Erysipeloid: A bacterial infection (Erysipelothrix rhusiopathiae) typically acquired from animals or contaminated animal products, which can cause skin lesions and abscesses, though it's more commonly associated with the hands.

Each diagnosis is considered based on the clinical presentation, patient history, and potential risk factors. The justification for including these diagnoses involves considering common causes of underarm abscesses, conditions that could mimic or lead to abscess formation, and rare but potentially serious infections that should not be overlooked.