Differential Diagnosis for Non-blanching Purpura, Fever, Right Arm Edema, and Pruritus

• Single Most Likely Diagnosis

  • Henoch-Schönlein Purpura (HSP): This condition is characterized by non-blanching purpura, fever, and often edema, particularly in the extremities. The presence of pruritus can also be seen in HSP, making it a strong candidate given the combination of symptoms.

• Other Likely Diagnoses

  • Cellulitis: While typically presenting with warmth, redness, and swelling, cellulitis can sometimes cause non-blanching purpura, especially if there's an underlying vascular issue. The edema and fever are consistent with cellulitis, but the pruritus is less common.
  • Deep Vein Thrombosis (DVT): DVT can cause edema and warmth in the affected limb, and in some cases, may lead to purpura if there's associated skin necrosis or inflammation. However, non-blanching purpura is not a typical primary presentation.
  • Insect Bite or Sting Reaction: Certain insect bites or stings can cause localized edema, pruritus, and potentially non-blanching purpura if there's a significant allergic reaction. Fever might be present in the case of an infection.

• Do Not Miss Diagnoses

  • Septic Phlebitis: This is a serious condition that can present with fever, edema, and purpura, especially if the infection involves the superficial or deep veins. It's crucial to consider this diagnosis due to its potential for severe complications.
  • Necrotizing Fasciitis: Although rare, this condition is a medical emergency. It can present with edema, fever, and purpura, along with severe pain out of proportion to the physical findings. The presence of pruritus might be overshadowed by the pain.
  • Meningococcemia: This condition, caused by Neisseria meningitidis, can present with fever, non-blanching purpura, and sometimes edema. It's a life-threatening condition that requires immediate diagnosis and treatment.

• Rare Diagnoses

  • Ehlers-Danlos Syndrome with associated vascular fragility: This could potentially lead to easy bruising and non-blanching purpura, along with other systemic symptoms.
  • Purpura Fulminans: A rare, life-threatening condition characterized by rapid progression of hemorrhagic necrosis of the skin, usually accompanied by fever and can be associated with edema and pruritus in the early stages.
  • Autoimmune disorders like Lupus or Rheumatoid Arthritis: These can cause a wide range of symptoms including purpura, fever, and edema, but the combination with pruritus is less common and would typically be accompanied by other systemic symptoms.