Psoriasis

Overview:

• Is a common papulo-squamous disorder affecting 2% of the population
• Characterised by well demarcated, red scaly plaques
• The skin becomes inflamed and hyperproliferates to about 10x the normal rate
• Males = females

The age of onset occurs in 2 peaks:

• Early onset (16-22 years) – more common and is associated with a +ve family history
• Late onset (55-60 years)

Pathology:

• Skin biopsy shows acanthosis and Parakeratosis, reflecting the increase in skin turnover
• The granular layer is often absent
• Polymorphonuclear abscesses may be seen in the upper epidermis

Types of psoriasis:

• Chronic plaque psoriasis
• Flexural psoriasis
• Guttate psoriasis
• Erythrodermic and pustular psoriasis

Chronic plaque psoriasis:

• This is the ‘common’ type of psoriasis
• Is characterised by pinkish red scaly plaques, especially on:
• Knees
• Elbows
• Lower back
• Ears
• Scalp

• New plaques of psoriasis may occur at sites of skin trauma (so-called Kobner phenomenon)
• The lesions can become itchy or sore

Flexural psoriasis:

• Tends to occur in later life
• Characterised by well demarcated red glazed plaques confined to flexures such as the:
• Groin
• Natal cleft
• Sub-mammary area

• Rarely there is any scaling
• In the absence of psoriasis elsewhere, the rash is often misdiagnosed as candida intertrigo

Guttate psoriasis:

• ‘Raindrop-like’ psoriasis is a variant most commonly seen in children and young adults
• An explosive eruption of very small circular or oval plaques appears over the trunk about 2 weeks after a Streptococcal sore throat
• It usually resolves spontaneously over 1-2 months even without treatment

Erythrodermic ad pustular psoriasis:

• These are the most severe types of psoriasis, reflecting a widespread intense inflammation of the skin
• They can occur together (‘Von Zumbusch’ psoriasis) and may be associated with:
• Malaise
• Pyrexia
• Circulatory disturbance, this form can be life-threatening

• The pustules are not infected, but are sterile collections of inflammatory cells
• There is also a more localised variant of pustular psoriasis that confines itself to the hands and feet, but is not associated with severe systemic symptoms

Associated features:

Nails:

• Up to 50% of patients develop nail changes and rarely these can precede the onset of skin disease
• There are 5 types of nail change:
• Pitting of the nail-plate
• Distal separation of the nail-plate (onycholysis)
• Yellow-brown discolouration
• Subungual hyperkeratosis
• Rarely, a damaged nail matrix and lost nail-plate

• Treatment of nail dystrophy is very difficult

Arthritis:

• Up to 5% of patients develop psoriatic arthritis and most of these will have nail changes
• There are 5 patterns of psoriatic arthritis:
• Distal interphalangeal arthritis
• Peripheral mono- or oligoarthritis
• Symmetrical ‘rheumatoid arthritis pattern’ but seronegative
• Spondylitis or sacro-iliitis (especially HLA-B27 +ve)
• (Rarely) arthritis mutilans – causing destruction and resorption of bone leading to telescoping of affected digits

Prognosis:

• Most individuals who develop chronic plaque psoriasis will have the condition for life
• It fluctuates in severity and there are no available tests to predict outcome
• Guttate psoriasis resolves spontaneously and in up to 30% of individuals does not recur
• However, 70% will go on to get recurrent guttate attacks or will progress to chronic plaque psoriasis

Treatment:

• This is concerned with control rather than cure
• Most patients can be improved with topical therapies:
• Mild-to-moderate topical steroids
• Calcipotriol (a synthetic vitamin D₃ analogue)
• Purified coal tar

• Salicylic acid can be a useful adjunct
• All should be applied bds to palpable lesions
• Once lesions have flattened, therapy can be discontinued
• UV therapy is also useful

Use of methotrexate:

• Normally given once weekly
• Some patients experience extreme nausea on the day they take it
• Regular blood tests need to be done to monitor for bone marrow suppression and liver damage
• Alcohol must be avoided as this increases the risk of hepatotoxicity
• Long-term users will need a liver biopsy every 2-3 years to accurately monitor for hepatic damage