Differential Diagnosis for Red Painful Areas

The following differential diagnosis is based on the presentation of red painful areas, which could be related to various conditions.

• Single most likely diagnosis:
  • Cellulitis: This is a common bacterial skin infection characterized by redness, warmth, swelling, and pain. It often starts as a small area of redness that spreads rapidly.
• Other Likely diagnoses:
  • Eczema/Dermatitis: Conditions that cause inflammation of the skin, leading to redness, itching, and sometimes pain.
  • Psoriasis: An autoimmune condition that speeds up the life cycle of skin cells, causing cells to build up rapidly on the surface of the skin. The extra skin cells form scales and red patches that itch or burn.
  • Contact Dermatitis: A type of inflammation of the skin that occurs when the skin comes into contact with an irritant or allergen, leading to redness, itching, and pain.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Necrotizing Fasciitis: A serious bacterial infection that destroys the tissue under the skin, including fat and the tissue covering the muscles (fascia). It's characterized by severe pain, redness, and swelling, and can be life-threatening if not treated promptly.
  • Erythema Migrans (Lyme Disease): An early stage of Lyme disease, characterized by a distinctive expanding red rash, which can be painful and is a critical diagnosis to make due to the long-term consequences of untreated Lyme disease.
• Rare diagnoses:
  • Erythema Multiforme: A skin condition characterized by target lesions, which are often symmetrically distributed and can be painful. It's considered rare and can be triggered by infections or medications.
  • Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): A rare skin condition marked by the sudden onset of fever, leukocytosis, and tender, erythematous, well-demarcated papules and plaques that histologically show dense neutrophilic infiltrates without evidence of vasculitis.