Differential Diagnosis for Axilla Boil

• Single most likely diagnosis
  • Furuncle (boil): This is the most common cause of a boil in the axilla, typically resulting from a bacterial infection, often Staphylococcus aureus, of a hair follicle.
• Other Likely diagnoses
  • Carbuncle: A cluster of furuncles connected subcutaneously, also usually caused by Staphylococcus aureus, which can appear in the axilla.
  • Hidradenitis suppurativa: A chronic skin condition characterized by recurrent, painful abscesses and nodules in apocrine-gland-bearing areas, such as the axillae.
  • Folliculitis: An inflammation of the hair follicles, which can be caused by bacterial, viral, or fungal infections and can present similarly to a boil.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Cat-scratch disease: Although less common, this disease caused by Bartonella henselae can lead to lymphadenopathy and abscesses, including in the axilla, after a cat scratch or bite.
  • Tuberculosis: Cutaneous tuberculosis, though rare, can manifest as abscesses or boils in various parts of the body, including the axilla, and is critical to diagnose due to its public health implications and the need for specific treatment.
  • Actinomycosis: A rare bacterial infection that can cause abscesses, including in the axilla, and requires long-term antibiotic treatment.
• Rare diagnoses
  • Erysipelas: A type of skin infection that can cause raised, red patches, typically on the face but occasionally on other areas, including the axilla.
  • Mycobacterial infections (other than tuberculosis): Such as Mycobacterium avium complex, which can cause skin infections, including abscesses, especially in immunocompromised individuals.
  • Sporotrichosis: A fungal infection caused by Sporothrix schenckii, which typically enters the body through cuts or scrapes in the skin and can cause lesions or boils, often on the arms.