Dr Tess McPherson

Brief Outline: Dr Tess McPherson is a Consultant Dermatologist, Senior Clinical Senior Lecturer at the University of Oxford and member of the British Society of Paediatric Dermatology.

Background: Dr Tess McPherson is a Consultant Dermatologist and Senior Clinical Lecturer (Oxford University Hospitals). Her particular areas of clinical and research interests include paediatric dermatology, teenage and young adult dermatology, psoriasis, acne and eczema.

Dr McPherson talks about some of the types of psoriasis.

So psoriasis is a kind of umbrella term for a type of inflammation of the skin, where you've got sort of scaly plaques. And there are several different types. The most common by far is something called chronic plaque psoriasis. And that's the one which is probably about one to two percent of the population have chronic plaque psoriasis, so it's not quite as common as eczema, but it's really not uncommon. It's often quite a hidden disease, I think people often feel quite stigmatised if they've got even a small amount of psoriasis. So they will, you know, often not sort of show their skin, or expose their skin to people. And that's the type of psoriasis where you often get it on the elbows, you can get it on the scalp, and it tends to be, as the name suggests, it's chronic. Tends to come and go, depending on different, you know times of life. But that's- and it has quite a strong genetic link. So if you've got parents with psoriasis, you're more likely to get that one. There's another, the other sort of common type of psoriasis, and it's a more reactive type of psoriasis, is called guttate psoriasis. And that you see with a sort of particular trigger. So you may have an infection, such as streptococcal throat infection, or something like that, and then you get a, that sort of triggers off your kind of immune system to produce very small little droplets of psoriasis often, in this kind of guttate picture. So sort of on someone's back, in smaller plaques. If you have guttate psoriasis, you know you're more prone to chronic plaque psoriasis, because some of the things are quite similar.

And those are, you know. But within the plaque psoriasis, you can be subdivided into, you know, which part of your body it's affecting. So genital psoriasis, scalp psoriasis, so there’s, you know, a lot, every person with psoriasis will have a different pattern of disease. But the sort of similarities would be type of skin changes you get, the sort of clearly marked out plaques of psoriasis, often with a sort of silvery scale. And then there are associated types of psoriasis, so you can get- your nails can be affected, with nail psoriasis.

Dr McPherson explains what happens with the skin in psoriasis.

So in psoriasis, you see here's the normal skin. You've got your cells here, and the epidermis, nice and tightly packed together. And that's the hair coming out of the hair follicle. And actually what happens in psoriasis, is this bit of the skin, the epidermis gets very thick and inflamed. And that's why you see these sort of red plaques with scale on them, so. Hopefully you can see the difference here. You've got all these cells packed on top of each other. That's the scale you see with psoriasis. And you can actually see this very- so this is what a thick plaque of psoriasis- so the skin's much thicker. The cells are sort of over-producing to form these thick plaques. So they actually have a very sort of, you know, thicker layer. And actually- as opposed to eczema, actually kind of an increased kind of barrier function. But it still can cause drying, because of all the scaliness, and that's why we do use moisturiser in psoriasis, as well as other treatments.

But mostly it's a lot of inflammation, a lot of kind of cell turnover, to produce these thickened areas of skin.

Dr McPherson talks about the role of genetics in psoriasis.

So psoriasis is like eczema, another very complex disease with lots of different things playing a role. But it's probably kind of pro-inflammatory state, which you inherit some genes which make you more at risk of it. There's not one gene for psoriasis, there's lots of genes, it's kind of, you know, is a complex disorder. But we do know if you've got one or two parents with psoriasis, you yourself are more likely to get psoriasis, and your brothers and sisters are more likely to have psoriasis. So it definitely runs in families. The trait runs in families. But like a lot of these very complex conditions, it seems like something will then trigger it off. So it may be infection, it might be a stressful event, you know, other things can therefore trigger off the kind of inflammatory pathways of psoriasis.

Dr McPherson discusses infections and stress as known triggers for psoriasis.

So triggers that we know can either cause a flare of psoriasis or initiate psoriasis. Particular types of infections. So in children and young adults, often streptococcal. So that can cause throat infections, it can also cause skin infections. So sometimes I do see children who have [throat cleared] a streptococcal infection in the genital area, or around the bottom, and that can also sort of trigger off psoriasis more generally. We know that also stressful events and stress can definitely exacerbate and trigger psoriasis. And we're now kind of starting to understand a little bit more about the whole inflammatory pathways that stress causes. And, you know, clearly having psoriasis also makes you feel stressed, so it can be quite a difficult process to sort of work out what best to do about it. Which is why, you know, psychological support is so vital for people, particularly with psoriasis, and that, you know, coping mechanisms are also really important.

Dr McPherson talks about psoriatic arthritis.

So, psoriatic arthritis is similar to the inflammation you get in the skin. You can get an inflammation in the joints. And probably in about ten to fifteen percent of people you can get that inflammation in the joints. That can come before the skin, with the skin, after the skin manifestations, and it can happen in, you know-. It sometimes-, more often associated with nail psoriasis, so lifting of the nails or pitting of the nails can be seen in people with joint disease as well. And it's a destructive arthritis. So it's very important to get that treated by a rheumatologist, because there's inflammation in the joints, you can actually get destruction of the joints as well. And that would definitely be an indication for thinking about tablet treatments for psoriasis.

Dr McPherson talks about the benefits of sunlight and the use of phototherapy for psoriasis.

So lots of people will recognise their psoriasis or their skin is better in the summer, if they do expose their skin. But unfortunately lots of people with psoriasis won't feel able to expose their skin, you know, for reasons of kind of shame or stigmatisation. So actually we know that a lot of people with psoriasis are actually vitamin D deficient because they won't- even though it's helpful for them to, you know, have sunlight on their skin, they won't. Sunlight is a, is a powerful anti-inflammatory, and it seems to work particularly on the type of inflammation you get in psoriasis. And light treatment uses that fact, but we have the, the wavelength of light we use is the sort of one that's been shown by some people in America to be the most effective to reduce inflammation. And the least sort of risk long term with skin cancer. So we use a particular wave of light called narrowband UVB. Which is, that's why the light boxes are particularly designed to be used for patients with psoriasis, rather than just going on a sun bed or going sort of sun bathing. But it does mean you have to come to the department, and you have to come regularly, to have the sort of light sort of dose built up over time.

Dr McPherson discusses the risks associated with phototherapy treatment.

So there are risks to light treatment. You know, no treatment is without risks, unfortunately, and that's why you always have to be very careful when you're dealing with a condition which is likely to be to some extent life-long. That you don't want to use treatments that give you higher risks than the benefits you get. And that's why using things that suppress your immune system long term, the biological drugs, you know, all these things which can be very helpful with psoriasis, we just have to be careful about how young you start them, how long you're on them for. And we have to really have really good sort of long term data. The light treatment, certainly if you are fair skinned, you know, it does give you an increased risk of skin cancer long term. We try and minimise that by using this particular wavelength that's, you know, that's less- considered to be less carcinogenic than say UVA or the type of light you might get in a sun bed. But still, you know, clearly having light therapy does increase your risk to some small degree. And that's why again, we'll count up how many courses someone has and there's quite sort of clear guidelines about how much light you should have over a lifetime.

Dr McPherson says it’s not possible to always predict who will benefit from each type of systemic treatment or who will get side effects.

And then you've got tablet types of treatments, or injections. The tablet treatments that are kind of licensed and we use regularly for psoriasis, there's one called methotrexate. Which can be, you know, very effective and- but it does need regular blood tests because it can cause problems with your, your blood counts and you liver. And then you've got other tablets as well, which work in completely different ways. And we haven't yet got a test- so we can't look at someone and say, “Your psoriasis is gonna respond best to this treatment, and your psoriasis is gonna respond best to this treatment.” Maybe in the future we'll be able to do that sort of thing, where we can actually say- you know, take a test and tell them which treatment they're gonna respond best to. And that's an area of active research. But at the moment we have lots of different treatments which work in very different ways. And sometimes it's a case of trial and error. 

Dr McPherson talks about how decisions are usually made about trying a biological treatment and, if so, which one.

There are lots of different ones. So there's quite strict criteria that come from, you know, both local kind of commissioning groups and from NICE about what type of psoriasis and how severe the psoriasis needs to be before you could even be considered for a biologic. So your first line would be the other medicines, first of all. So you would think about normal treatment first of all. If there was a reason why you couldn't have one of them or you'd had side-effects or poor response and you have severe psoriasis at a certain level - so that's both - psoriasis measured but there’s something called a PASI, which is how widespread and how severe it is, and also by how much it's affecting that person. So a Life Quality Index would also have to be of a certain level. And if those two things are within the criteria, then you would be considered for a biologic. In terms of which one to choose, I mean, that's gonna be a decision made between the doctor and your patient. But there's different classes. So the ones that have been around for like, for the longest, are something called anti-TNF medications or biologics. And they're, you know, probably still considered, you know, first line by most people because they've been used for longest on the most patients so they've probably got the most safety data. There's a new class, which is- so there's one that's also been used for quite a long time, which is called ustekinumab. Which is an anti- slightly different cytokine targets. Very effective for, can be very effective for psoriasis. Probably not so effective for the arthritis psoriasis. But it's licensed in teenagers. But only the anti-TNFs are licensed in younger children. So, you know, you'd have to take into consideration what's licensed. You know, eligibility criteria. And then you'd discuss on a kind of case by case basis. There's no right or wrong answer. 

Dr McPherson talks about how common psoriasis is and how long it tends to last.

Psoriasis is probably more common than most people think, about 2% of the population have psoriasis. And psoriasis can occur or start at any age from baby to, you know, I recently saw someone who had their first psoriasis in her 80s. So you can get psoriasis really at any point in your life. Psoriasis is not-, it tends to be a chronic disease but it depends on the type of psoriasis you’ve got. The form that’s kind of reactive to infections or sometimes medications is less likely to be chronic in that you can have a one-off episode of something called guttate psoriasis. Or you can have psoriasis which is triggered by a medication which improves when you come off the medication. The most common type of psoriasis, chronic plaque psoriasis, which has quite high heritability so you’re more likely to get it if your family’s got it, it doesn’t have a cure – doesn’t mean it can’t be controlled but it means you are more likely to have it through your life. And that’s the most common sort of psoriasis we see. So, and it’s quite a common time to get psoriasis is in your teenage years. So young people, young adults, it’s quite a common time to have your first symptoms of psoriasis. 

And for the majority of people, they are likely to have some issues or problems with psoriasis ongoing from the time they first present with it. That doesn’t mean again that it’s not controllable or there aren’t lots of things that can be done to manage it, but it does mean there’s no sort of cure. But that’s really true for lots of chronic conditions, you know. We talk about hypertension as being- we don’t talk about hypertension as not having a cure, we talk about it as having ways to manage it. And I think some of these more chronic inflammatory skin diseases it’s the same type of issues – that you can manage them but you can’t say, “You’re never going to have any psoriasis ever again all your life”.