Psoriasis in Darker Skin: Epidemiology and Pathophysiology

00:01 Welcome to our lecture on psoriasis.

00:04 Psoriasis is a chronic non-contagious inflammatory disease characterized by patches of dry, sometimes itchy, and scaly skin.

00:16 It may also be associated with arthritis.

00:20 It's relatively common in adults and children, affecting about 0.5% to 11% of people worldwide.

00:30 Roughly up to 3% of the individuals affected are in the US.

00:35 It can be seen at any age, but incidence peaks at the age of 20 to 30 and between 50 and 60 years, with an average of about 28 years.

00:46 One-third of patients have a first-degree relative with with psoriasis.

00:52 There tends to be a seasonal variation with psoriasis, and it tends to be worse in winter than summer and is slightly more prevalent in women.

01:02 More cases are seen in Caucasians and Asians than in Africans.

01:09 The risk factors include use of tobacco and alcohol.

01:14 Patients who are obese. Infections can also trigger psoriasis, as well as stress and different weather conditions.

01:27 Psoriasis is a complex inflammatory skin and joint condition.

01:31 While its exact cause is not fully understood, it is believed to involve combination of genetic, environmental, and immune factors.

01:44 The major histocompatibility complex genes are a group of genes that encode proteins that are crucial for immune systems functioning.

01:55 The shortest one is the first identified psoriasis susceptibility locus, which has a specific region on chromosome six.

02:05 Multiple studies have identified other regions that increase the risk of developing psoriasis.

02:12 Genetic variations in these regions affect how the immune system responds to different triggers.

02:21 Individuals with HLA -B27 subtype of HLA -B gene have higher chance for developing psoriatic arthritis. So that's it on pathogenesis of psoriasis.

02:38 So we've covered the genetic and immunological factors.

02:42 Now let's take a look at environmental factors that can trigger psoriasis infections.

02:49 As we mentioned streptococcus can lead to guttate psoriasis.

02:54 Human immunodeficiency virus which we spoke about can also cause erythroderma psoriasis, where more than 90% of the body surface area is involved.

03:04 In fact, during the HIV era, we found that many of our African patients were developing erythroderma psoriasis, something that we didn't see as much before the HIV epidemic. Cold weather could be a triggering factor as well as trauma, which can also lead to Koebner phenomenon.

03:29 Medications like lithium, beta -blockers and antimalarials are the most common triggers in terms of drug use, so it's important that you get this history from patients who develop psoriasis.

03:44 Alcohol and tobacco use, as I've mentioned, can also trigger psoriasis or make it even worse.

03:50 And obesity has been associated with psoriasis.

03:54 Smoking, pregnancy and stress can trigger or exacerbate psoriasis.

04:03 So let's take a quick look at the pathophysiology of psoriasis.

04:08 It is triggered by a combination of genetic and environmental factors as mentioned previously.

04:13 However, in a number of patients the exact trigger is unknown.

04:19 These triggers activate immune cells, especially T cells that then migrate to the dermis and epidermis. They then released different inflammatory mediators that over time cause various cutaneous changes. In the epidermis one can see, particularly on histology, epidermal hyperplasia, as well as accelerated cell turnover rate.

04:44 So normally it takes about 23 days for the cell to move from the basal layer to the stratum corneum.

04:52 However, this process is accelerated in psoriasis, taking about ii.

04:57 3 to 5 days. And this results with on with parakeratosis because the cell gets there faster before it loses its nucleus.

05:07 And then you get poorly adherent stratum corneum as well as flaking.

05:13 And what about the dermis.

05:14 What do we see in the dermis.

05:16 Again these are some of the histological features of psoriasis.

05:21 You see elongated dermal papillae as well as dilated blood vessels which become tortuous and leaky.