Differential Diagnosis for Pruritic Rash in a 69-year-old Male with COPD
- Single most likely diagnosis:
- Contact Dermatitis: Given the patient's occupation as a warehouse employee who unloads trucks, exposure to new or irritating substances is possible, even if he is unaware of any new chemicals or products. The rash started on the trunk and spread to other areas, which could be consistent with contact dermatitis, especially if the causative agent was something he came into contact with at work.
- Other Likely diagnoses:
- Atopic Dermatitis (Eczema): Although the patient started Dupixent (an medication for atopic dermatitis) 2 months ago without side effects, it's possible that his condition is not well-controlled, or he could be experiencing a flare. The pruritic nature of the rash supports this diagnosis.
- Drug Rash: Despite the patient not reporting any side effects from Dupixent, drug rashes can occur at any time. It's essential to consider the medication as a potential cause, especially since it's the only medication change mentioned.
- Seborrheic Dermatitis: This condition can cause a pruritic rash on the trunk, face, and neck, which aligns with the patient's symptoms. It's common in adults and can be exacerbated by stress or environmental factors.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN): Although rare, these conditions are life-threatening and can be triggered by medications or infections. The patient's rash spreading to the face and neck, along with the potential for medication involvement (despite no previous side effects), makes it crucial not to miss these diagnoses.
- Angioedema: Given the patient's history of COPD and the potential for medication side effects, angioedema is a critical diagnosis not to miss, especially if there's any involvement of the respiratory tract, which the patient denies.
- Rare diagnoses:
- Pityriasis Rosea: This condition can cause a pruritic rash that starts on the trunk and spreads, but it's less common in older adults and typically follows a viral infection.
- Cutaneous T-cell Lymphoma (Mycosis Fungoides): A rare condition that can cause skin lesions and rashes, often pruritic. It's essential to consider in the differential diagnosis, especially if the rash does not respond to standard treatments.