What is the biological link between depression and psoriasis?

Biological changes are involved in the association between depression and psoriasis. During psoriasis, the following changes are observed:

• The blood levels of interleukin 12 (IL-12), IL-1 alpha, IL-2, and IL-6 increase;

• The level of Substance P is revised upwards;

• The levels of Tumour Necrosis Factor α (TNF-α) and interferon α are elevated;

• The level of serotonin, also known as the happiness hormone, decreases.

The cytokines IL-2, IL-6, TNF-α and interferon α are known to play a role in the onset of depression symptoms. Cytokines can influence the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the stress response. Prolonged activation of this axis can lead to excessive production of cortisol, a stress hormone, which can disrupt emotional balance and lead to depression.

Psychiatric disorders are likely to develop in cases of psoriasis. They particularly develop in a young population. Indeed, 25 to 30% of children with psoriasis, without any psychiatric history, are prone to depression, anxiety, and even bipolar disorder. Thus, the disease affects the patient's personality. It interferes not only in daily life, but also in emotional and professional choices.

Emerging in the field of QoL (Quality of Life), the main psychological impacts of psoriasis are a lack of self-confidence and a feeling of stigmatisation. Furthermore, psoriasis patients constantly feel repulsive, which exacerbates anxiety and depression. Suicidal thoughts become frequent. Studies reveal that they are estimated to be between 2.5 and 9%, and particularly affect young people, women, and hospitalised patients.

There are measurement scales in place to define the contours of depression associated with psoriasis. Among them, we can mention:

• The Primary Care Screener for Affective Disorders (PCSAD);

• The General Health Questionnaire-12 (GHQ-12);

• The Patient Health Questionnaire-9 (PHQ-9);

• The Beck Depression Inventory (BDI);

• The Hospital Anxiety and Depression Scale (HADS);

• The Mini International Neuropsychiatric Interview (MINI).

Once depression is identified, the dermatologist refers the patient to a mental health professional. This could be a psychiatrist or a psychodermatologist. Depending on the severity of the depression, they may prescribe either a non-pharmacological treatment, such as cognitive-behavioural therapy, or a pharmacological treatment. The latter could include benzodiazepines, selective serotonin reuptake inhibitors (SSRIs), doxepin, and buspirone.