Plaque psoriasis is characterised by raised and easily palpable lesions, owing to the thickened epidermis, expanded vascular compartment as well as infiltrate of neutrophils and lymphocytes. The plaques are well defined with sharply demarcated boundaries. The scales tend to be silvery-white, which when removed lead to some capillary bleeding. The lesions are more commonly found on the scalp, trunk, intergluteal cleft and limbs with a predilection for the extensor surfaces such as the elbows and knees. Pruritus can be severe in some of the cases.
Guttate psoriasis: Is described as a raindrop-type rash of multiple psoriasis areas appearing on the trunk of patients, usually some two to three weeks after an upper respiratory tract infection.
It occurs in people younger than 30 years of age and often resolves within 20 weeks, but a significant number will progress to plaque psoriasis. Most studies have found evidence of recent streptococcal infection in the majority (up to 93%) of patients with acute guttate psoriasis.
Patients with these lesions may sometimes need to be treated with antibiotics to eliminate carrier states.
Pustular psoriasis: Is an uncommon form of psoriasis consisting of widespread pustules on an erythematous background. It may affect the palms and soles or rarely lead to a generalised erythroderma.
Cutaneous lesions characteristic of psoriasis vulgaris may be present before, during or after an acute pustular episode. Pruritus, intense burning, fever, erythroderma, hypocalcaemia and cachexia are usually observed. Other systemic complications may include acute respiratory distress syndrome, pneumonia, congestive heart failure and hepatitis. Episodes of pustular psoriasis can be evoked by withdrawal of systemic corticosteroids as well the use of certain drugs, like iodides, coal tar, minocycline and salicylates. The treatment of choice is oral retinoids, which can result in quick relief. Other oral treatments are also very effective.
Nail psoriasis: Can be easily mistaken for onychomycosis. The nails may exhibit pitting, onycholysis, subungual hyperkeratosis or the oil drop sign. The disease tends to affect most nails and is usually associated with plaque psoriasis elsewhere. A good history and examination are necessary to distinguish it from a fungal infection. The treatment mainly entails the use of oral medications as topical creams cannot be applied to the nail bed. Some authorities also advocate the use of scalp preparations of corticosteroids to be applied around the nails, which can be effective in very mild cases.
Psoriatic arthritis: Can occur in up to 30% of patients with skin disease. It affects any age and typically starts around a decade after the onset of skin lesions.
The symptoms can range from mild to severe, and there is no correlation between the severity of skin lesions and that of the joints. The patients complain of morning stiffness, pain, swelling of joints, pain in ligaments and tendons that is variable and unpredictable with flares and remissions. There is a definite association between HLA-B27 and radiological evidence of sacroiliitis. However, there are probably other genes that are associated with psoriatic arthropathy.
When these symptoms are present, patients need to be treated aggressively and referred to a rheumatologist to stabilise their condition before the onset of permanent joint damage.
References available on request.