Differential Diagnosis for Itchy Circular Rash

• Single most likely diagnosis
  • Eczema/Dermatitis: This is often the first consideration for itchy, circular rashes due to its high prevalence and the fact that it can present in various forms, including atopic dermatitis, contact dermatitis, and seborrheic dermatitis. The circular shape can be due to the way the skin reacts to irritants or allergens.
• Other Likely diagnoses
  • Ringworm (Tinea corporis): A common fungal infection that causes circular, itchy rashes. It's highly contagious and can be spread by skin-to-skin contact or through contaminated objects.
  • Psoriasis: While psoriasis can cause a variety of skin lesions, it sometimes presents as circular, itchy plaques, especially in its guttate form.
  • Nummular dermatitis: Characterized by coin-shaped patches of dry, itchy skin, often appearing after a skin injury, such as a burn, abrasion, or insect bite.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Lyme disease: Caused by a tick bite, Lyme disease can initially present with a circular, expanding rash known as erythema migrans, which is often accompanied by itching. Missing this diagnosis can lead to serious complications if left untreated.
  • Erythema multiforme: A skin condition characterized by target lesions, which can sometimes appear circular and itchy. It can be a sign of an underlying infection or drug reaction and requires prompt attention.
• Rare diagnoses
  • Granuloma annulare: A rare skin condition that causes a circular rash, typically without itching, but can sometimes be itchy. It's characterized by a ring of small bumps.
  • Secondary syphilis: Can cause a variety of skin rashes, including circular ones, though these are less common. The rash of secondary syphilis can be accompanied by itching.
  • Cutaneous lymphoma: Certain types of skin lymphoma can present with itchy, circular lesions, though this is quite rare and usually part of a more complex clinical picture.