Differential Diagnosis for Rash

The following is a comprehensive differential diagnosis for a rash, categorized for clarity and emphasis on critical conditions.

• Single Most Likely Diagnosis
  • Eczema (Atopic Dermatitis): This is a common condition characterized by itchy, inflamed skin. It's often seen in individuals with a history of allergies or asthma, making it a frequent diagnosis in patients presenting with a rash.
• Other Likely Diagnoses
  • Contact Dermatitis: An allergic or irritant reaction to substances like metals, latex, or certain chemicals, leading to a rash. This is common in individuals who have recently started using new personal care products or have been exposed to potential allergens.
  • Psoriasis: An autoimmune condition leading to thick, scaly, red patches on the skin. It's a likely diagnosis in patients with a family history of psoriasis or those presenting with characteristic lesions on the elbows, knees, or scalp.
  • Viral Exanthems: These are rashes caused by viral infections, such as measles, chickenpox, or roseola. They are common in children and often accompanied by fever and other systemic symptoms.
• Do Not Miss Diagnoses
  • Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a rash (petechiae or purpura) and is life-threatening if not promptly treated. It's crucial to consider this diagnosis in patients with a rash and signs of sepsis.
  • Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN): A severe skin condition usually triggered by medications, leading to widespread skin necrosis and detachment. It's a medical emergency requiring immediate attention.
  • Lyme Disease: Caused by Borrelia burgdorferi, transmitted by tick bites, and can present with a characteristic "bull's-eye" rash (erythema migrans). Missing this diagnosis can lead to late-stage complications affecting the heart, joints, and nervous system.
• Rare Diagnoses
  • Kawasaki Disease: An acute febrile illness of childhood that presents with a rash, among other symptoms like fever, lymphadenopathy, and desquamation of the hands and feet. It's rare but important to diagnose early to prevent cardiac complications.
  • Pemphigus: A group of autoimmune diseases characterized by blistering of the skin and mucous membranes. It's rare and requires specific diagnostic tests for confirmation.
  • Syphilis: A sexually transmitted infection that can cause a variety of skin rashes, depending on the stage of the disease. It's less common in some populations but remains an important consideration due to its potential for serious complications if left untreated.