Differential Diagnosis

The patient presents with itching and a rash over the upper body, which has been ongoing for a few weeks. The symptoms initially improved with a short course of prednisone but have since recurred. The patient also reports a possible reaction to a medication in a patch delivery system, which was stopped, and suspects an allergy to a new mattress. Considering these details, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Contact Dermatitis: This is the most likely diagnosis given the patient's history of a new mattress and a possible reaction to a medication patch. Contact dermatitis is a type of inflammation of the skin that occurs when the skin comes into contact with an irritant or allergen, leading to symptoms like itching, redness, and a rash. The improvement with prednisone and the recurrence after stopping also support this diagnosis, as corticosteroids are commonly used to treat contact dermatitis.

• Other Likely Diagnoses

  • Atopic Dermatitis (Eczema): Although the patient's symptoms seem to be triggered by external factors, atopic dermatitis is a common condition characterized by itchy, inflamed skin, and could be considered, especially if the patient has a history of allergies or asthma.
  • Drug Rash: Given the patient's report of a possible reaction to a medication in a patch delivery system, a drug rash is a plausible diagnosis. The rash could be a result of an allergic reaction to the medication or an irritant effect.
  • Allergic Contact Dermatitis to the Mattress: This could be due to materials in the mattress, such as latex, certain fabrics, or chemicals used in the manufacturing process.

• Do Not Miss Diagnoses

  • Bullous Pemphigoid: An autoimmune disease that can cause blistering of the skin. It's less common but can be severe and requires prompt treatment.
  • Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN): Although rare, these are life-threatening conditions usually triggered by medications. They cause widespread skin necrosis and detachment, and early recognition is crucial for survival.
  • Cutaneous T-Cell Lymphoma (CTCL): A type of skin cancer that can present with skin patches, plaques, or rashes, and can be mistaken for more benign conditions.

• Rare Diagnoses

  • Dermatitis Herpetiformis: A chronic skin condition characterized by blisters filled with a watery fluid. It's associated with celiac disease and is rare.
  • Pityriasis Rubra Pilaris (PRP): A rare skin disorder that causes constant itching and scaling (exfoliation) of the skin, which can be mistaken for other dermatological conditions.
  • Erythema Multiforme: An immune-mediated disorder that can cause skin lesions, which might resemble other rashes but has distinct target-like lesions.

Each of these diagnoses should be considered in the context of the patient's full medical history, physical examination, and potentially, further diagnostic testing such as skin biopsies or patch testing for allergies.