Psoriatic arthritis - The Feet

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The presence of “sausage” toes is one of the “supportive” features in the criteria for diagnosis of PsA. The pain of PsA of the feet is often the dominant feature to sufferers and a potent cause of disability. It is surprising that descriptions of foot involvement in psoriasis (including the skin problems of onycholysis and plantar pustular psoriasis) are given so little prominence in textbooks.

In about 4% of patients enthesopathy may precede the onset of arthritis. Plantar fascciiitis with calcaneal spur formation is the commonest type seen. Early morning heel pain and foot stiffness which resists all forms of treatment (eg injection, physiotherapy, heel pads) for 6 months, most particularly if bilateral should alert a clinician to the possibility of an inflammatory systemic condition. PsA and sero-negative spondylarthritis are the two commonest conditions that present like this and patients should be watched carefully. Enthesopathy may accompany all forms of PsA in 40% of sufferers and may need specific treatment locally for symptom control.

Although PsA can be confused with rheumatoid arthritis (RA), when it presents as a symmetrical polyarthritis of the metacarpal and metatarso-phalangeaal joints, it can usually be distinguished by involvement of other more specific joints and the absence of rheumatoid factor in the blood. It is more common for this type of arthritis to be assymmetrical and to involve only the first matatarso-phalangeal joint, together with one or two interphalangeal joints. Erosions of many small joints may be seen on X-rays. The combination of erosion, absence of rheumatoid factor, sausage digits and involvement of the first interphalangeal joint is typical of PsA. Other joints in the feet, especially the fifth metatarso-phalangeal and ankle joints may also become painful and swollen but less commonly so.

The initial symptoms of foot arthritis are of pain and swelling, warmth, and stiffness. Morning stiffness does occur in PsA, but is far less dominant than RA. Evening stiffness and swelling with limited walking distance are the commonest problems to patients. The wearing of shoes for more than a few hours at a time and the need to change shoe height, weight and width two or three times a day are familiar features to patients and clinicians alike.

More long-term the feet can become deformed. This can occur remarkably quickly - within 6 months if the arthritis is not adequately treated. The usual deformities are clawed toes, hyperextension of the big toe and some inrolling of the ankle with flattening of the metatarsal arch. Stiffness of the joints rather than instability also happens quickly and can again become irreversible within a few months. The occurrence of calluses and ulcers on the soles of the feet is less common than in RA but “corns” over the interphalangeal joints can be very painful.
Despite this seemingly depressing description, the nature of PA in the majority of cases, is to be milder than RA.

The arthritis is more circumscribed, milder in onset and subject to long periods of remission. This means that disability is less but as far as the feet are concerned,
can work against adequate treatment. Both patients and clinicians tend to ignore the symptoms and deformity and stiffness can develop insidiously. This leads to future problems including osteoarthritis, tendon contractures, calluses and disability. These features may be prevented if treatment is adequate.

The treatment of the feet in PsA must initially include a full assessment of the involved joints and tendons. A walking assessment should be included together with the usual blood tests, full history and X-Rays. If suppressive medication is considered necessary this should be started promptly. The slow action (3 months) of such drugs means that any delay in initiating treatment can allow the development of erosions and deformity.

Local treatment to the feet is always necessary to some degree. This may include corticosteriod injections to the worst involved areas (painful but effective for up to 6 months), anti-inflammatory gels and physiotherapy. Anti-inflammatory and analgesic drugs will also be needed to control pain initially. The advice of a podiatrist (chiropodist) should be sought also.

It is vitally important that the patient understands from the outset the importance of joint protection and exercise and the effects that weight-bearing and footwear can have both for good and bad on the feet. Advice early in the course of the arthritis from a physiotherapist and/or a podiatrist can do much to prevent deformity. The patient should be told to remeasure length and width of his or her feet (not many adults bother to do this after the age of 21) and purchase shoes that are both wide, deep and long enough to encompass swollen feet, have deep soles and support of the arches and ankles. Invariably this excludes some female fashion shoes, although some modern boots are of excellent design. Clinicians can do no more about this potential battle-ground than point out the dangers of unsuitable shoes. Unfortunately fashion and power dressing are the usual winners.

Patients also need to learn the type of mobilising and stretching exercises that will prevent stiffness and deformity. These should be carried out every day even when the arthritis is active and should always be done non-weight bearing. Massage baths, hand massage and gravity assistance can also be used for symptom control as part of the regime.

If deformity has already developed or if plantar fasciitis causes a painful limp, shoe inserts may be needed. Here a chiropodist or skilled orthotist can be invaluable. Silicone gel and various synthetic materials can help to redistribute weight. There is a new silicone gel and mineral substance incorporated into heel and toe caps which is proving very popular with patients which is now obtainable. Surgical shoes and more sophisticated splints are seldom necessary except for the severest cases. Similarly orthopaedic surgery for correction of deformed joints is only justified in the presence of long-standing deformity where pain is preventing adequate mobility and all alternative medical treatments have failed.

PsA of the feet can be a potent cause of pain and disability. Adequate recognition and treatment of the problem is seldom ideal. If addressed early this form of arthritis can be properly treated and much future pain prevented. Such treatment needs a multi-disciplinary approach in partnership with the patient.

Author:
Dr.A.V.Camp FRACP
Consultant Rheumatologist

First published: 1995: Skin 'n' Bones Connection. Issue 4, p11-14