Differential Diagnosis for Blanching Rash
- Single most likely diagnosis
- Erythema multiforme: This condition is characterized by a blanching rash that can appear as target lesions, making it a common cause of such symptoms. It often follows a viral infection or can be triggered by medications.
- Other Likely diagnoses
- Urticaria (hives): Although typically pruritic and transient, some forms of urticaria can present with blanching rashes. The lesions can vary in size and shape and may be associated with allergic reactions or autoimmune conditions.
- Contact dermatitis: This is an inflammatory skin condition caused by contact with irritants or allergens, leading to a rash that may blanch. It's less likely to be the primary consideration for a blanching rash but should be considered, especially if the rash is localized.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Meningococcemia: This is a severe infection caused by Neisseria meningitidis, which can present with a blanching rash that progresses to purpura. It's critical to identify this condition early due to its high mortality rate if left untreated.
- Rocky Mountain spotted fever: Caused by Rickettsia rickettsii, this tick-borne illness can start with a blanching rash that later becomes petechial. Early diagnosis and treatment are crucial to prevent severe complications.
- Rare diagnoses
- Kawasaki disease: An acute febrile illness of childhood characterized by a blanching rash, among other symptoms like fever, lymphadenopathy, and desquamation of the hands and feet. It's rare but important to consider due to its potential for cardiac complications.
- Henoch-Schönlein purpura (HSP): Although HSP typically presents with a non-blanching purpuric rash, some early stages or variants might be considered in the differential for a blanching rash, especially if there are other systemic symptoms like abdominal pain or arthritis.