Psoriasis is the most common inflammatory dermatosis , having a prevalence of 0.1 – 1.5 % across countries . 1 It is a T-cell mediated disorder ( with a dominant IL-23 / Th17 axis ). It presents as well-demarcated erythematous plaques and patches with silvery scales . 1 Different subtypes include plaque , palmoplantar , gutatta , pustular , inversa / flexural , nail and erythrodermic . 1
The skin lesions vary in size and are commonly situated on extensor areas of the knees and elbows , scalp and the buttocks . 1
It is associated with a number of comorbidities including psoriatic arthritis ( in up to 20 % of patients ), metabolic syndrome , inflammatory bowel disease ( see later article in this handbook ) cardiovascular disease , and psychological disorders .
Hidradenitis suppurativa ( HS ; also known as acne inversa ) is another inflammatosis in which the IL-23 / Th17 pathway is expressed . 6 It is a long-term , severely debilitating condition that presents as inflammation of hair follicles causing painful nodules and abscesses . Lesions might also associate with pruritus and malodour . Its pathogenensis includes follicular hyperkeratosis and dilatation and rupture , and inflammation ( acute and chronic ). Risk factors include possible relation to bacterial infection , mechanical forces , smoking , and genetic mutations . Comorbidities associated with HS include metabolic syndrome , cardiovascular disease , type 2 diabetes , IBD , spondyloarthropathy , polycystic ovarian syndrome and psychological disorders ( depression , suicide , substance use disorders , sleep and sexual dysfunctions ). 6
It has an estimated prevalence of 0.00033 – 4.1 % globally ( but most likely 0.7 – 1.2 % in the European-US population ). 6 The main characteristics ( prevalence , pathogenesis , cutaneous manifestations , and associated comorbidities ) of other common inflammatory dermatoses are detailed in Table 1 .
TABLE 1
Characteristics of inflammatory dermatoses
Disease AD 7 – 9 AA 10 , 11 Vitiligo 12
Prevalence 1.7 – 32.8 % ( children ), 1.2-9.7 % ( adults )
1.82 – 2.42 % 0.06 – 2.28 %
Pathogenesis |
Predominantly by an enhanced Th2 inflammation , mediated by genetic predisposition , epidermal barrier dysfunction , skin microbiome abnormalities , inadequate antimicrobial peptides , and alterations in the neuroimmune system |
Loss of the immune privilege system . Mediated by cytotoxic T-cells |
CXCR3 + CD8 + T-cells promote melanocyte apoptosis through interferon-gamma secretion and chemokines secreted by keratinocytes through the JAK / STAT signaling pathway , with further recruitment of T-cells |
Cutaneous manifestations |
Recurrent eczema and severe itching |
Non-scarring hair loss of the scalp and other body sites . Patchy , totalis ( all scalp hair ), universalis ( all body hair ). Regrowth up to 80 % ( patients with limited patchy hair loss of < 1 year ) |
Progressive achromic macules / patches due to loss of skin pigment and melanocytes , which increase over time |
Comorbidities Atopic diseases ( food allergies , asthma , allergic rhinoconjunctivitis and eosinophilic esophagitis ), cardiometabolic conditions , obesity , psychological and attention disorders , cancer , and other AI diseases ( AA , vitiligo , LE , chronic urticaria or IBD )
AI diseases , atopic diseases , Helicobacter pylori infection , MS , LE , iron deficiency anemia , thyroid diseases , psychiatric diseases , vitamin D deficiency , and audiologic / ophthalmic abnormalities
AD , psoriasis , thyroid disease , AA , SLE , rheumatoid arthritis , DM , IBD , scleroderma , SS , dermatomyositis , pernicious anaemia , Addison ’ s disease , ocular and audiological abnormalities
AI , autoimmune ; AA , alopecia areata ; LE , lupus erythematosus ; MS , metabolic syndrome ; IBD , inflammatory bowel disease ; CVD , cardiovascular disease ; DM , diabetes mellitus ; SS , Sjögren syndrome ; SLE , systemic lupus erythematosus .
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