Differential Diagnosis for a Rash on the Back and Chest

• Single most likely diagnosis
  • Tinea Versicolor: A common fungal infection that causes discolored patches on the skin, often found on the back and chest. It's more likely in warm and humid environments and can be associated with oily skin.
• Other Likely diagnoses
  • Acne: Especially on the back (bacne) and chest, acne can cause a rash-like appearance due to comedones, papules, pustules, or cysts.
  • Eczema (Atopic Dermatitis): Can present as a rash on various parts of the body, including the back and chest, characterized by itchy, inflamed skin.
  • Contact Dermatitis: An allergic reaction or irritation from substances like soaps, detergents, or metals can cause a rash on the back and chest.
  • 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.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Meningococcemia: A severe infection that can cause a rash, often starting as small, red-purple spots that can quickly spread and turn into large bruises. It's a medical emergency.
  • Rocky Mountain Spotted Fever (RMSF): A bacterial infection that can cause a rash, fever, and headache. The rash usually appears 2-5 days after the onset of fever and can be deadly if not treated promptly.
  • Lyme Disease: Caused by a tick bite, it can lead to a distinctive "bull's-eye" rash, though not all cases present with this symptom. It's crucial to consider in endemic areas.
• Rare diagnoses
  • Pityriasis Rubra Pilaris (PRP): A rare skin disorder that causes constant inflammation and scaling (exfoliation) of the skin. It can start with a reddish-orange rash on the face, then spreads to other parts of the body.
  • Kawasaki Disease: An illness that affects the blood vessels and can cause a rash, among other symptoms like fever, swollen lymph nodes, and swelling of the hands and feet. It's more common in children but can occur in adults.