Differential Diagnosis for Rashes in Pregnancy

When considering a rash in pregnancy, it's crucial to approach the diagnosis systematically to ensure all potential causes are considered. The differential diagnosis can be organized into several categories based on likelihood and potential impact.

• Single Most Likely Diagnosis

  • Polymorphic Eruption of Pregnancy (PEP): Formerly known as pruritic urticarial papules and plaques of pregnancy (PUPPP), this is the most common dermatosis in pregnancy, occurring in about 1 in 160 pregnancies. It typically presents in the third trimester with intense itching and a rash that starts in the abdominal striae and can spread to other areas.

• Other Likely Diagnoses

  • Atopic Eruption of Pregnancy (AEP): This includes atopic dermatitis, which can be exacerbated by pregnancy. It's characterized by dry, itchy skin and can be managed with moisturizers and topical corticosteroids.
  • Pemphigoid Gestationis (PG): An autoimmune blistering disease that occurs during pregnancy, typically in the second or third trimester. It presents with severe itching followed by blister formation.
  • Prurigo of Pregnancy: Characterized by extremely itchy nodules, often on the arms and legs. The exact cause is unknown, but it may be related to dry skin.

• Do Not Miss Diagnoses

  • Preeclampsia with HELLP Syndrome: While not primarily a skin condition, preeclampsia can sometimes present with a rash or petechiae due to thrombocytopenia and coagulopathy. It's critical to consider this diagnosis due to its severe implications for both mother and fetus.
  • Infections (e.g., Varicella, Herpes Simplex, and Zika): Certain infections can cause rashes and have significant implications for the fetus, including congenital abnormalities and neonatal illness.
  • Thrombotic Thrombocytopenic Purpura (TTP): A rare blood disorder characterized by clotting in small blood vessels throughout the body, which can lead to a petechial rash among other symptoms.

• Rare Diagnoses

  • Intrahepatic Cholestasis of Pregnancy (ICP): While primarily known for causing severe itching without a primary rash, some patients may develop a secondary rash due to scratching. It's a condition that affects the liver and can increase the risk of premature birth and stillbirth.
  • Acute Fatty Liver of Pregnancy: A rare but serious condition that can cause a range of symptoms, including sometimes a rash, due to liver dysfunction.
  • Cholestasis of Pregnancy with Skin Manifestations: Rarely, cholestasis can lead to specific skin changes, though this is less common than the primary symptom of itching.

Each of these conditions has a different approach to management and treatment, emphasizing the importance of a thorough differential diagnosis when a rash is identified in pregnancy.