Differential Diagnosis for Red Painful Rash

• Single most likely diagnosis
  • Cellulitis: This is a common condition characterized by a red, painful, and swollen rash, often caused by bacterial infection. It's likely due to its high prevalence and the match with the symptoms described.
• Other Likely diagnoses
  • Eczema (atopic dermatitis): A chronic condition that can cause red, itchy, and painful rashes. It's a common skin condition that could fit the description.
  • Contact dermatitis: An allergic or irritant reaction causing a red, painful rash after exposure to certain substances. This is a plausible diagnosis given the symptoms.
  • Psoriasis: An autoimmune condition leading to red, scaly, and painful patches on the skin. It's a possible diagnosis, especially if the rash is chronic.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Necrotizing fasciitis: A severe bacterial infection that destroys tissue under the skin, requiring immediate medical attention. Although rare, it's critical to consider due to its high mortality rate.
  • Toxic epidermal necrolysis (TEN) or Stevens-Johnson syndrome (SJS): Severe skin conditions usually triggered by medications, leading to widespread skin necrosis and detachment. These conditions are medical emergencies.
  • Rocky Mountain spotted fever: A tick-borne illness that can cause a red, painful rash and has a high mortality rate if not treated promptly.
• Rare diagnoses
  • Erythema multiforme: An immune-mediated condition characterized by target-like lesions, which can be painful and is often triggered by infections or medications.
  • Sweet syndrome (acute febrile neutrophilic dermatosis): A rare condition marked by fever, neutrophilia, and tender, erythematous skin lesions. It's an uncommon diagnosis but should be considered in the appropriate clinical context.