Psoriasis
Date: Thursday, January 15, 2009 @ 22:13:56 :: Topic: Dermatology
The familiar pink or red lesions with a scaling surface and well defined edge are easily recognised.
These changes can be related to the histological appearance:
• The increased thickness of the epidermis, presence of nuclei above the basal layer, and thick keratin are related to increased epidermal turnover.
• Because the epidermis is dividing it does not differentiate adequately into normal keratin scales.
These are readily removed to reveal the tortuous blood vessels beneath, appearing clinically as “Auspitz sign”.
The psoriatic plaque can be likened to a brick wall badly built by a workman in too much of a hurry it may be high but it is easily knocked down.
• The polymorphs that migrate into the epidermis form sterile pustules in pustular psoriasis.
These are most commonly seen on the palms and soles.
• The dilated blood vessels can be a main feature, giving the clinical picture of intense erythema.
The equivalent changes in the nail cause thickening and “pits” 0.5–1.0 mm in diameter on the surface; these are thought to be due to small areas of psoriatic changes in the upper layer of the nail plate that then fall out.
Onycholysis, in which the nail plate is raised up, also occurs in psoriasis.
Clinical appearance
The main characteristics of psoriatic lesions, which reflect the pathological processes listed above, follow. Plaques consisting of well defined raised areas of psoriasis.
These may be few or numerous, covering large areas of the trunk and limbs.
Sometimes there are large confluent lesions.
Scaling may predominate, giving a thick plaque, which is sometimes likened to limpets on the sea shore, hence the name “rupioid”. Scratching the surface produces a waxy appearance the “tache de bougie” (literally “a line of candle wax”).
Erythema may be conspicuous, especially in lesions on the trunk and flexures. Pustules are rare on the trunk and limbs, but deep seated pustules on the palms and soles are fairly common.
In the form of palmo-plantar pustulosis they may occur without psoriasiatic lesions elsewhere.
The size of the lesions varies from a few millimetres to very extensive plaques.
The typical patient
Psoriasis usually occurs in early adult life, but the onset can be at any time from infancy to old age, when the appearance is often atypical.
The following factors in the history may help in making a diagnosis:
• There may be a family history if one parent has psoriasis 16% of the children will have it, if both parents, the figure is 50%.
• The onset can occur after any type of stress, including infection, trauma, or childbirth.
• The lesions may first appear at sites of minor trauma Koebner’s phenomenon.
• The lesions usually clear on exposure to the sun.
• Typically, psoriasis does not itch.
• There may be associated arthropathy affecting either the fingers and toes or a single large joint.
Clinical presentation
Patients usually present with lesions on the elbows, knees, and scalp.
The trunk may have plaques of variable size and which are sometimes annular.
Patients with psoriasis show Koebner’s phenomenon with lesions developing in areas of skin trauma such as scars or minor scratches.
Normal everyday trauma such as handling heavy machinery may produce hyperkeratotic lesions on the palms.
In the scalp there is scaling, sometimes producing very thick accretions.
Erythema often extends beyond the hair margin.
The nails show “pits” and also thickening with separation of the nail from the nail bed (oncholysis).
Guttate psoriasis from the Latin gutta, a drop consists of widespread small pink macules that look like drops of paint.
It usually occurs in adolescents and often follows an acute beta haemolytic streptococcal infection.
There may be much distress to both parent and child when a previously healthy adolescent erupts in spots.
Fortunately it also resolves quite rapidly.
Pustular lesions occur as either chronic deep seated lesions or generalised pustular psoriasis.
Chronic deep seated lesions occur on the palms and soles with surrounding erythema which develops a brown colour and scaling.
It is important to reassure the patient that, despite their appearance, these pustules are not infectious they consist of sterile collections of polymorphs.
These lesions occur in an older age group than psoriasis, and psoriasis may not be present elsewhere.
It is more common in smokers.
Acrodermatitis pustulosa is a variant that occurs in a younger age group in which there are pustules and inflammation arround the nails and the fingertips.
Generalised pustular psoriasis is uncommon.
Pustules develop in association with erythema.
It may be precipitated by the use of steroids.
Flexural psoriasis produces well defined erythematous areas in the axillae and groins and beneath the breasts.
Scaling is minimal or absent.
It must be distinguished from a fungal infection and it is wise to send specimens for mycology if there is any doubt.
Napkin psoriasis in children may present with typical psoriatic lesions or a more diffuse erythematous eruption with exudative rather than scaling lesions.
Erythrodermic psoriasis is a serious, even life threatening, condition with erythema affecting nearly the whole of the skin.
Diagnosis may not be easy as the characteristic scaling of psoriasis is absent, although this usually precedes the erythroderma.
Less commonly the erythema develops suddenly without preceding lesions.
There is a considerable increase in cutaneous blood flow, heat loss, metabolism, and water loss.
It is important to distinguish between the stable, chronic, plaque type of psoriasis, which is unlikely to develop exacerbations and responds to tar, dithranol, and ultraviolet treatment, and the more acute erythematous type, which is unstable and likely to spread rapidly.
The use of tar, dithranol, or ultraviolet light can irritate the skin and will make it more widespread and inflamed.
Joint disease in psoriasis
Patients with seronegative arthropathy of the non-rheumatoid type show double the normal (2%) incidence of psoriasis.
Psoriatic arthropathy commonly affects the distal interphalangeal joints, sparing the metacarpophalangeal joints, and is usually asymmetrical.
Radiological changes !include! a destructive arthropathy with deformity.
Rheumatoid nodules are absent.
The sex ratio is equal but a few patients develop a “rheumatoid-like” arthropathy, which is more common in women than in men.
A third rare group have arthritic changes in the larger joints, where there is considerable resorption of bone.
Other members of the families of those with psoriatic arthropathy are affected in 40% of cases.
There may be pustular psoriasis of the fingers and toes associated with arthropathy which can be sufficiently severe to immobilise the patient.
Both psoriatic arthropathy and Reiter’s syndrome are associated with the presence of HLA B27.
Reiter’s syndrome is characterised by polyarthritis and the development of urethritis, inflammatory changes in the conjunctivae, and skin lesions including pustulosis hyperkeratosis of the soles.
Causes of psoriasis
The cause is unknown but there is an inherited predisposition.
The strong genetic influence may result from a single dominant gene with poor penetrance or a number of genetic influences.
Other factors such as local trauma, general illness and stress are also involved, so the cause of psoriasis is best regarded as being multifactorial.
HLA-Cw6 is the phenotype most strongly associated with psoriasis, particularly the early onset variety in which hereditary factors seem to play the greatest part.
There is an increase in HLA expression in psoriatic arthropathy.
Local trauma, acute illness, and stress may be factors in causing the appearance of clinical lesions.
Beta Haemolytic streptococcal throat infection is a common precipitating factor in guttate psoriasis.
Antimalarial drugs, lithium, and Beta blockers can make psoriasis worse.
There is evidence that psoriasis occurs more readily and is more intractable in patients with a high intake of alcohol. Smoking is associated with palmo-plantar pustulosis.
There is evidence that both hormonal and immunological mechanisms are involved at a cellular level.
The raised concentrations of metabolites of arachodonic acid in the affected skin of people with psoriasis are related to the clinical changes.
Prostaglandins cause erythema, whereas leukotrienes (LTB4 and 12 HETE) cause neutrophils to accumulate.
The common precursor of these factors is phospholipase A2, which is influenced by calmodulin, a cellular receptor protein for calcium.
Both phospholipase A2 and calmodulin concentrations are raised in psoriatic lesions.
T helper lymphocytes have been found in the dermis as well as antibodies to the basal cell nuclei of psoriatic skin.
In addition, dermal factors contribute to the development of psoriatic lesions.
The detailed treatment of psoriasis is covered in the next chapter.
The only point to be made here is the importance of encouraging a positive attitude with expectation of improvement but not a permanent cure, since psoriasis can recur at any time.
Some patients are unconcerned about very extensive lesions whereas to others the most minor lesions are a catastrophe.
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