Erythrodermic Psoriasis: What is this rare form of psoriasis?

Erythrodermic psoriasis is a rare but severe form of plaque psoriasis. Individuals affected by this form require immediate hospitalisation, as it is potentially dangerous, especially for older individuals. Its manifestation causes red, scaling lesions that cover more than 80% of the body. Its prevalence is estimated to be between 1 and 2.25% in patients with psoriasis.

The manifestation of erythrodermic psoriasis is accompanied by several generalised skin signs such as erythema, oedema, pruritus, poorly defined psoriatic plaques, desquamation, exudative lesions and palmoplantar peeling. Nail changes are very common in erythrodermic psoriasis and can range from a slight puncture to severe onychodystrophy. Chills, fever or even an acceleration of the heart rate can be observed.

The causes of this pathology are not yet fully understood. However, certain assumptions are made: scientists believe that this type of psoriasis involves a complex interaction of Th1, Th2 lymphocytes, and Th17 inflammatory pathways. They think that a Th1/Th2 imbalance tends to favour Th2 differentiation and its related cytokines, which would be involved in the onset of this disease. Further studies need to be conducted to understand how this pathology occurs.

Erythrodermic psoriasis can present complications similar to those of pustular psoriasis, such as thermoregulation disorders. These occur when the hypodermis of the skin is destroyed and psoriasis is present all over the body. The complications of erythrodermic psoriasis are as follows:

• From a fever;

• Of a risk of infection;

• Of a heart failure;

• Regarding a dehydration issue;

• Of protein losses;

• Of swelling in the legs and a malnutrition issue.

Dehydration is one of the reasons necessitating patient hospitalisation, as it poses a threat to their life. This action is required when the individual experiences a loss of heat, proteins, and bodily fluids.

Hospitalisation is necessary when treating erythrodermic psoriasis. Patients suffering from this disease must be placed under close monitoring to provide them with the necessary treatments. These may involve regulating the patient's body temperature and administering intravenous fluids. The management of this disease may involve:

• the patient's rest;

• the use of emollients and wet dressings;

• The intake of immunosuppressants (ciclosporin or methotrexate) which inhibit the enzyme dihydrofolate reductase, allows for the slowing down of cellular proliferation. They reduce inflammatory markers such as IL-6 and TNF-α to soothe the skin.

• The use of biotherapies with the aid of anti TNF-α (etanercept). These are soluble receptors that bind to TNF-α and prevent it from attaching to target cells, blocking the development of skin inflammation.

• Theuse of IL12/23 inhibitors: These two cytokines are involved in the pathogenesis of psoriasis by stimulating the Th1 and Th17 inflammatory pathways. By inhibiting them with an antibody such as ustekinumab, inflammation is reduced. Ustekinumab is approved for the treatment of moderate to severe plaque psoriasis and it is administered subcutaneously.

In the preliminary treatments of erythrodermic psoriasis, phototherapy should be avoided as it can exacerbate flare-ups. It can only be used when the disease is stable. In a clinical study, medical treatment based on corticosteroids taken orally has shown that it can worsen this form of psoriasis and therefore should be avoided in this type of psoriasis.

• BOYD A. S. & al. Erythrodermic psoriasis. Clinical Review (1989).

• SINGH R. K. & al. Erythrodermic psoriasis: pathophysiology and current treatment perspectives. Psoriasis: Targets and Therapy (2022).