Are psoriasis and atopic dermatitis separate diseases or part of the same spectrum?

This study from Denmark and the UK sought to answer the question: ‘Are psoriasis and atopic dermatitis (AD) in adults separate diseases or part of the same spectrum?’, one important consideration being that management and research may be less well targeted if they are lumped together. 10,128 people in Denmark participated: 3348 with psoriasis, 3834 with AD and 2946 from the general population. They were sent photographs to score how their skin was affected, and asked about lifestyle and the ways the conditions affected them. Both conditions tended to run in families, and severity for each was linked with onset early in life, frequent flare ups and being overweight. AD mostly began in childhood, psoriasis mostly in adult life with one peak early (associated with severe disease and family members affected) and another later in life. Patients with psoriasis in general (not just severe cases) were less physically active and more overweight than AD patients in general, and more likely to smoke than the general population; unless on methotrexate, patients with severe psoriasis tended to drink more alcohol than either other group. Asthma was much commoner in AD, and severe AD more prone to frequent flare ups than psoriasis. Quality of life scores were worse for AD, and joint pain worse for psoriasis. The study confirmed the body sites known to be affected by both conditions, but also highlighted the neck and skin between the fingers in AD. Either condition may be generalised, and features can overlap in severe cases. The authors concluded that psoriasis and AD were best viewed as separate diseases. Linked Article:   Egeberg et al. Br J Dermatol 2020; 183 :128–138.