Psoriasis is a common, chronic, recurrent inflammatory skin disease with characteristic erythematous scaling that is triggered by multiple environmental factors in a genetic background.
The word “Psora” is Greek and means “white flaking”. The prevalence is 0.1-3% in China, 0.123% in China, urban 〉 rural, northern 〉 southern, and the incidence is higher in Northern Europe, which is related to race and geographical environment. It is common in young adults, and there is no difference between men and women.
Etiology and pathogenesis
1. Genetic factors.
In the census and genealogical analysis of psoriasis patients, it is found that psoriasis has a more obvious genetic tendency. Most scholars’ surveys show that about 10-39% of patients have a family history. Domestic family history accounts for 10-17% and foreign 10-80%, which is considered polygenic inheritance. Patients with positive family history have earlier onset.
Genealogical analysis
The proportion of children with psoriasis is higher among parents with psoriasis;
In the offspring, the ratio of male to female incidence is close to 1:1;
There are both autosomal dominant and autosomal recessive families;
An epidemiological data from the United States in 2007 showed that
If you have psoriasis yourself, then
your unrelated neighbors have a risk of about 2% (geographic or climatic factors)
Your siblings have a risk of about 15-20% (genetic factors)
Your identical twin brother or sister has a risk of about 65-70% (genetic)
Your offspring’s risk is about 25% (genetic factors)
The above data are from the United States. The prevalence is significantly higher in European and American whites than in Asian yellows, and detailed epidemiological data are not available for China.
Dizygotic method analysis
The age of onset, rash distribution, and the extent and course of symptoms are very similar in monozygotic twins, but not in dizygotic twins.
HLA antigens and psoriasis
In the HLA system, antigens A1, A13, A28, B13, B17, B37 and C6, and DR7, a class II antigen, are expressed more frequently in patients with psoriasis than in normal subjects, with HLA-C6 being particularly associated with psoriasis.
Chromosomal studies
Six susceptibility loci for psoriasis were identified by whole gene scan, including 6q, 17q, 4q, 1q, 3q and 19q, among which, 4q31 is a susceptibility locus specific to Han Chinese. However, the exact susceptibility gene or causative gene has not been found.
2.Environmental factors
Infection
Viral infection: eosinophilic inclusion bodies in the nucleus of spinal cells, retroviral particles in urine and scales, and no virus has been cultured yet.
Bacterial infection: about 6% of the pathology is related to pharyngitis, 10%-20% of pediatric psoriasis is accompanied by tonsillitis and upper respiratory tract infection, anti “O” increased, penicillin and other treatments are effective, there are also cases of skin lesions receding after tonsil removal. Acute punctate, arthritic, and erythrodermic patients often have a history of epiglottitis or tonsillitis before the onset of the disease, all suggesting that bacterial infection is associated with the onset of the disease.
Fungal and other microbial infections
3.Metabolic factors
Keratin-forming cells: proliferation is accelerated and the mitotic cycle of cells is shortened, which also shortens the turnover time of epidermis.
Polyamines: metabolites of amino acids in the body, involved in protein biosynthesis, and play a regulatory role in cell proliferation. Polyamines are significantly higher in psoriatic lesions compared to normal skin.
Cyclophosphoglycoside (cAMP): cAMP is an epidermal inhibitor that inhibits epidermal cell division. Some scholars believe that the abnormal proliferation of psoriatic epidermis is related to cAMP, while others believe that it is related to the increased ratio of cGMP (cyclophosphoguanosine)/cAMP.
4.Immune factors
Immune regulation disorder: psoriasis is a disease related to abnormal immune regulation, especially the infiltration of local lymphocytes in the skin lesion, the disorder of T lymphocyte regulation, and the excessive secretion of Th1 cytokines IL-2 and IFN-r, leading to the excessive proliferation of psoriatic epidermal basal stem cells, the shortening of cell division cycle, the disappearance of granular layer and incomplete keratinization, which results in clinical erythema, plaques and scales.
Cytokines: A variety of cytokines secreted by immune cells are involved in the pathological process of psoriasis, such as IL-1 , IL-2, IL-8 and IFN-γ, which can stimulate the proliferation of keratin-forming cells, and vascular endothelial growth factor and endothelin, which are involved in the expansion and proliferation of dermal capillaries.
Predisposing factors
Psychoneurological factors
Mental tension, stressful events, overexertion or strong mental stimulation can trigger or aggravate psoriasis, and the onset of psoriasis is closely related to mental factors in 30%-40% of patients.
Psoriasis is therefore considered to be a psychosomatic disease. Psychotherapy and biofeedback therapy are applied and produce certain efficacy.
Smoking
Smoking is an important trigger for the development of psoriasis. An Italian case-control study showed that the risk of psoriasis in former and current smokers was 1.7 and 1.9 times higher than in never-smokers. High-intensity smoking (>20 cigarettes/d) more than tripled the risk of more severe clinical manifestations of psoriasis compared to low-intensity smoking (≤10 cigarettes/d). Studies have shown that smoking has a greater impact on women.
Alcohol consumption
Alcohol consumption can trigger or exacerbate the pathological process of psoriasis itself. Alcohol consumption can directly dilate blood vessels and increase vascular permeability, which facilitates neutrophil outflow and epidermal infiltration; at the same time, alcohol consumption increases arachidonic acid content, inhibits adenylate cyclase, reduces CAMP and increases CGMP, leading to epidermal cell proliferation.
Food
Studies have confirmed that consumption of fish and shrimp is a more important predisposing factor. This may be related to the fact that fish and shrimp are high-protein foods that cause skin allergy. Some studies have analyzed that the low incidence of psoriasis in Africa is due to its unique diet (maize is a major component of their diet) in addition to genetic factors. olters et al. found that appropriate fasting, consumption of low-calorie diets, and vegetarian diets helped psoriasis patients improve their condition.
Dampness
Dampness is an important predisposing factor. Previous studies have confirmed that it is not uncommon for people to develop psoriasis after living in a damp place or after going into a field or getting wet. Some scholars found that 22.5% of the patients had an obvious relationship between the onset of the disease and humidity, because the skin is easily impregnated and eroded in a humid environment for a long time, especially when working underwater, and it is easy for a large number of bacteria to multiply and cause skin infections to develop. In addition, it was found that humidity stimulates epidermal DNA synthesis and enhances this synthesis reaction, which leads to epidermal hyperplasia.
Allergic factors
Some domestic studies have reported that about 10% of psoriasis patients are allergic to dust mites, dust and mold, and more psoriasis patients are allergic to fish, shrimp and crab in food, and some patients are allergic to beef and mutton, because allergy can trigger or aggravate psoriasis, so allergen testing can be performed for psoriasis patients when necessary.
Trauma and surgery: can aggravate or induce psoriasis.
Endocrine and pregnancy: It may be related to the abnormal function of thyroid, adrenal gland and thymus, etc. Pregnancy can relieve the onset of psoriasis.
Drugs: drugs that may induce psoriasis include: beta-blockers (antihypertensive drugs), lithium (psychiatric drugs), antimalarials, anti-inflammatory pain (analgesics), terbinafine (antifungal drugs), calcium channel blockers (nicardipine, nifedipine, etc., all of which are antihypertensive drugs).
Other: e.g. race, climate, geography.