Differential Diagnosis

The patient presents with a rash that started on the abdomen and spread to the legs, breast, and inner thigh, accompanied by itching but no fever. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis
  • Atopic Dermatitis (Eczema): This condition is characterized by itchy, inflamed skin and can start on the abdomen before spreading to other areas. The absence of fever and the presence of itching are consistent with this diagnosis.
• Other Likely Diagnoses
  • Contact Dermatitis: This could be due to an allergic reaction or irritant causing a rash and itching, which can spread upon continued exposure to the offending agent.
  • Seborrheic Dermatitis: Although it more commonly affects the scalp, face, and ears, it can also appear on the torso and cause itching.
  • Pityriasis Rosea: Often starts with a herald patch on the trunk, followed by a wider rash that can spread to the limbs, though it typically doesn't cause significant itching.
• Do Not Miss Diagnoses
  • Bullous Pemphigoid: An autoimmune disease that can cause large blisters and significant itching. Although less common, missing this diagnosis could lead to severe complications.
  • Cutaneous T-Cell Lymphoma (Mycosis Fungoides): A rare type of skin cancer that can mimic eczema or dermatitis, making it crucial not to miss, despite its low likelihood.
• Rare Diagnoses
  • Erythema Migrans (Lyme Disease): Typically presents as a single expanding lesion, but in rare cases, multiple lesions can occur, and it can cause itching.
  • Sarcoidosis: A condition that can cause skin lesions, among other systemic symptoms, though itching is less commonly a primary symptom.

Each of these diagnoses has a different set of implications for treatment and management, emphasizing the importance of a thorough diagnostic workup.