Differential Diagnosis for Petechial Rash
- Single most likely diagnosis
- Contact Dermatitis: This is the most likely diagnosis given the itchy and painful nature of the rash, which started after hiking. The rash began on the wrist and progressed, suggesting exposure to an allergen or irritant during the hike.
- Other Likely diagnoses
- Insect Bite Reaction: The rash could be a reaction to insect bites, which is common after hiking. The itchy and painful nature of the rash supports this diagnosis.
- Allergic Contact Dermatitis to Plants: Plants like poison ivy, oak, or sumac can cause an allergic reaction, leading to a petechial rash. The timing and progression of the rash after hiking make this a plausible diagnosis.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Meningococcemia: Although rare, meningococcemia can present with a petechial rash and can be life-threatening if not treated promptly. The rash is often accompanied by fever, headache, and neck stiffness.
- Rocky Mountain Spotted Fever (RMSF): This tick-borne illness can cause a petechial rash, fever, and headache. Given the patient's recent hiking activity, RMSF is a potential diagnosis that should not be missed.
- Rare diagnoses
- Leptospirosis: This bacterial infection can cause a petechial rash, but it is relatively rare and usually associated with exposure to contaminated water or soil.
- Ehrlichiosis: Another tick-borne illness that can cause a petechial rash, although it is less common than other tick-borne diseases.
- Vasculitis: Certain types of vasculitis, such as Henoch-Schönlein purpura, can cause a petechial rash. However, these conditions are relatively rare and often have additional symptoms like abdominal pain, arthritis, or kidney involvement.