Paradoxical psoriasis, or psoriasiform paradoxical reactions, refers to the development or exacerbation of psoriasis following therapy with an antibody-based biologic agent. The onset may be weeks to months after starting the biologic therapy.

Dupilumab is a biologic therapy that is approved for treatment of atopic dermatitis, among other indications. It is one of the most common culprits that can trigger paradoxical psoriasis. A recent study shows that between 1.88% and 3.33% of dupilumab-treated patients reported this phenomenon. Tralokinumab, another biologic therapy indicated for atopic dermatitis, has been shown to induce paradoxical psoriasis as well.

Paradoxical psoriasis has also been reported in patients who receive biologic therapies indicated for psoriasis, whether they are prescribed for psoriasis or other indications, such as inflammatory bowel disease (Crohn disease, ulcerative colitis). Patients may develop worsening psoriasis or morphological change (eg, plaque-type switching to pustular-type) after initiation of biologic therapies, most commonly interleukin 17 (IL-17) and TNF-alpha antagonists, and less commonly IL-23 and IL12/23 inhibitors. It was first reported in patients treated with TNF-alpha antagonists and is thought to occur in 3.8%-10.7% of these patients. Patients may also develop psoriatic arthritis.

Paradoxical eczematous reactions have been reported in patients with psoriasis treated with biologic therapies as well (see eczematous drug eruption).

The mechanism behind these reactions is not well understood, but it is thought to be a phenotype switch associated with changes in the Th1/Th2 cytokine balance, secondary to biologic therapies.