Differential Diagnosis for High Grade Fever with Erythematous Pruritic Rash

Single Most Likely Diagnosis

• Viral Exanthem: This is often the most common cause of a rash with fever in both children and adults. Viral exanthems can be caused by a variety of viruses, including enteroviruses, adenoviruses, and parvovirus B19. The rash is typically erythematous and can be pruritic, and the fever is usually high grade.

Other Likely Diagnoses

• Allergic Contact Dermatitis: This condition occurs when the skin comes into contact with an allergen, leading to an immune response that causes inflammation and a rash. The rash can be erythematous and pruritic, and fever can occur if the reaction is severe.
• Bacterial Infections (e.g., Scarlet Fever, Impetigo): Certain bacterial infections can cause a rash and fever. For example, scarlet fever is caused by Group A beta-hemolytic streptococci and is characterized by a bright red, erythematous rash and high fever.
• Drug Rash: Many medications can cause a rash as a side effect, which can be accompanied by fever. The rash can be erythematous and pruritic.

Do Not Miss Diagnoses

• Meningococcemia: This is a life-threatening infection caused by Neisseria meningitidis. It can cause a rash that is typically petechial or purpuric, but can also be erythematous, along with high fever. Early recognition and treatment are crucial.
• Rocky Mountain Spotted Fever (RMSF): This is a tick-borne illness caused by Rickettsia rickettsii. It can cause a rash that is erythematous and pruritic, along with high fever. RMSF can be fatal if not treated promptly.
• Toxic Shock Syndrome: This is a severe condition caused by bacterial toxins, often produced by Staphylococcus aureus or Streptococcus pyogenes. It can cause a rash, fever, and other systemic symptoms, and is life-threatening if not recognized and treated early.

Rare Diagnoses

• Erythema Multiforme: This is an immune-mediated condition that can cause a characteristic target-like rash, which can be erythematous and pruritic. It is often associated with infections or medications.
• Kawasaki Disease: This is a rare condition that mainly affects children and can cause a rash, fever, and other symptoms. It is an important diagnosis to consider because it can lead to cardiac complications if not treated.
• Syphilis: In its secondary stage, syphilis can cause a rash that is erythematous and pruritic, along with fever. This diagnosis should be considered, especially in individuals with high-risk sexual behavior.