Differential Diagnosis for Itchy Facial/Arm Rash after Heat Exposure with Telangiectasias

• Single most likely diagnosis
  • Cholinergic Urticaria: This condition is characterized by an itchy rash that appears after exposure to heat, exercise, or emotional stress, which fits the symptoms described. The presence of telangiectasias (small dilated blood vessels near the surface of the skin) can also be seen in this condition due to the body's reaction to heat.
• Other Likely diagnoses
  • Heat Rash (Miliaria): Although more common in warmer climates and typically not associated with telangiectasias, heat rash can cause itchy skin lesions after heat exposure. It's a consideration, especially if the telangiectasias are not a prominent feature.
  • Solar Urticaria: This is a rare condition but can be considered if the rash appears specifically after sun exposure (a form of heat). It causes hives and itching after exposure to sunlight.
  • Polymorphic Light Eruption (PMLE): This is the most common form of photodermatosis, which could potentially present with itchy rash and possibly telangiectasias in some cases, especially if the heat exposure is combined with UV light.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
  • Systemic Lupus Erythematosus (SLE): Although less likely, SLE can present with a malar rash (butterfly-shaped rash across the cheeks) that worsens with sun exposure and can include telangiectasias. Missing this diagnosis could have severe consequences due to the potential for systemic involvement.
  • Porphyria Cutanea Tarda: This is a disorder that can cause blistering skin lesions upon sun exposure, and while less common, it's crucial not to miss due to its potential for severe skin manifestations and systemic implications.
• Rare diagnoses
  • Erythromelalgia: A disorder characterized by burning pain, heat, and redness in the hands and feet, and sometimes the face, which could potentially be confused with a rash and might include telangiectasias in some cases.
  • Poikiloderma of Civatte: A condition that affects the skin on the sides of the neck, characterized by a reticular (net-like) pattern of telangiectasias and skin discoloration, potentially exacerbated by heat or sun exposure.