Differential Diagnosis for Rash on Arms, Legs, and Abdomen

Single Most Likely Diagnosis

• Viral Exanthem: This is a common condition in children and adults, characterized by a rash that can start on the arms and legs and then spread to the abdomen. The rash is often accompanied by fever and other systemic symptoms. The most common viral exanthems include measles, rubella, and roseola.

Other Likely Diagnoses

• Allergic Contact Dermatitis: This condition occurs when the skin comes into contact with an allergen, leading to a rash. The rash typically starts at the site of contact and can spread to other areas, including the arms, legs, and abdomen.
• Atopic Dermatitis (Eczema): A chronic skin condition characterized by itchy, inflamed skin. The rash can appear anywhere on the body, including the arms, legs, and abdomen.
• Drug Rash: A rash that occurs as a reaction to a medication. The rash can appear anywhere on the body and can have various appearances.

Do Not Miss Diagnoses

• Meningococcemia: A life-threatening infection caused by Neisseria meningitidis. The rash can start as small, pink spots on the arms and legs and quickly progress to larger, purple spots that can appear on the abdomen. This condition requires immediate medical attention.
• Rocky Mountain Spotted Fever: A tick-borne illness that can cause a rash on the arms, legs, and abdomen. The rash typically appears 2-5 days after the onset of fever and can be accompanied by other systemic symptoms.
• Stevens-Johnson Syndrome: A rare but life-threatening condition that can cause a rash on the skin and mucous membranes. The rash can start on the arms and legs and spread to the abdomen, and is often accompanied by fever, sore throat, and conjunctivitis.

Rare Diagnoses

• Kawasaki Disease: A rare condition that primarily affects children, characterized by fever, rash, and swelling of the hands and feet. The rash can appear on the arms, legs, and abdomen, and is often accompanied by other systemic symptoms.
• Erythema Multiforme: A rare skin condition characterized by a rash that can appear on the arms, legs, and abdomen. The rash is often accompanied by fever and other systemic symptoms.
• Pityriasis Rosea: A rare skin condition characterized by a rash that can appear on the arms, legs, and abdomen. The rash typically starts with a single, large spot (herald patch) followed by smaller spots that can appear on the trunk and limbs.