Differential Diagnosis for Patient with Burning Rash and Systemic Symptoms

The patient presents with a burning rash on the trunk and top of thighs, accompanied by a low-grade fever, body aches, and headaches. The rash is described as painful and itchy, consisting of pink spots/circles and coalesced bumps. Based on these symptoms, the following differential diagnoses are considered:

• Single Most Likely Diagnosis
  • Viral exanthem (e.g., viral rash): This is a common cause of rash and systemic symptoms in adults, and the description of the rash as pink spots/circles and coalesced bumps is consistent with a viral etiology. The low-grade fever, body aches, and headaches also support this diagnosis.
• Other Likely Diagnoses
  • Contact dermatitis: The patient's rash could be an allergic or irritant reaction to a substance that came into contact with the skin, especially given the localized distribution on the trunk and thighs.
  • Eczema (atopic dermatitis): Although the patient's symptoms are somewhat atypical for eczema, the itchy and painful nature of the rash could suggest an eczematous process, particularly if the patient has a history of atopy.
  • Folliculitis: This is an inflammatory condition of the hair follicles, which could present with itchy, painful bumps, especially if the patient has been shaving or using harsh skin products.
• Do Not Miss Diagnoses
  • Stevens-Johnson Syndrome (SJS)/Toxic Epidermal Necrolysis (TEN): Although less likely, these conditions are life-threatening and require immediate attention. They can present with a rash, fever, and systemic symptoms, and any suspicion of SJS/TEN warrants prompt evaluation and treatment.
  • Infectious diseases (e.g., Lyme disease, syphilis, Rocky Mountain spotted fever): Certain infectious diseases can cause rashes and systemic symptoms, and it is crucial to consider these in the differential diagnosis, especially if the patient has been exposed to ticks or has other risk factors.
• Rare Diagnoses
  • Pityriasis rosea: This is a rare skin condition characterized by a herald patch followed by a secondary eruption of oval-shaped lesions, which could fit the patient's description of pink spots/circles and coalesced bumps.
  • Kawasaki disease: Although typically seen in children, Kawasaki disease can occur in adults and presents with fever, rash, and systemic symptoms, making it a rare but important consideration in the differential diagnosis.