From two studies (Lambert et al, 1976; Shore and Ansell, 1982), it was concluded that juvenile psoriatic arthritis is a distinct entity with one group of patients virtually indistinguishable from those with juvenile chronic arthritis initially, while all the patterns of psoriatic arthritis recorded in adults were seen in the remainder. A family history of psoriasis occurs in about half the patients, and one of arthritis in 20%. A swollen tendon sheath of a single finger or toe associated with synovitis in two or three joints of the digits is highly characteristic. Accurate diagnosis is important because these patients tend to go on to develop an asymmetrical destructive polyarthritis. This needs to be recognized early to utilize effective slow-acting drugs. Southwood and colleagues (1989) have defined two quite distinct groups of juvenile psoriatic arthritis: those young at onset, who are usually girls, and those in adolescence, who are more frequently boys. It is possible that there are other variants, including girls aged 8-10 years with a polyarthritic onset who may go on to develop arthritis mutilans. The concept of 'probable juvenile psoriatic arthritis' is supported by follow-up, in that a significant proportion of such patients do pass into the definite group. It is highly desirable that the suggested Vancouver criteria are validated by a long-term prospective study, which will probably need to be multicentred to ensure that the subgroups are large enough for satisfactory conclusions to be drawn. In the management of this serious arthritis in childhood, it is important to consider long-acting drugs early, before undue damage to joints has occurred. Again, multicentre studies are needed to determine which is the most useful. Presently, methotrexate appears to be the drug of choice.

Psoriatic skin disease is common; it occurs at all ages and co-exists with joint disease in approximately 10% of cases. All areas of skin, scalp and nails may be involved. In the typical case, the skin lesions are easy to recognize. Atypical forms of skin involvement and lesions at unusual sites are less easily diagnosed by non-specialists. The cause is unknown, but there is a clear genetic element, with external factors being important in precipitation and exacerbations of the condition. Topical treatment is successful in most patients, but in resistant cases combinations of systemic therapy and ultraviolet radiation usually give good control. Although there is no cure, the majority of sufferers live normal lives and, with the exception of severe erythrodermic or generalized pustular psoriasis, there is no mortality. Morbidity, particularly social and occupational, is more of a problem than is often acknowledged.

There is convincing evidence of a genetic basis for both psoriasis and psoriatic arthritis (PsA). Part of this genetic predisposition is due to genes within the major histocompatibility complex (MHC). In psoriasis, the primary association is with HLA-Cw6. Further work on specific nucleotide frequencies, especially those in the alpha 1 domain helix of the HLA-C molecule, will be of interest in determining whether a specific nucleotide frequency is present in all patients. The situation in PsA is considerably more complex. It is now established that there is an association between HLA-B27 and PsA, both in its peripheral arthropathy and in spinal disease in which radiological sacroiliitis is present. Spinal disease without radiological sacroiliitis is probably not associated with HLA-B27. There is some suggestion that HLA-B16 or its splits, HLA-B38 and HLA-B39, may also be associated with PsA, but there is considerable heterogeneity between the series, which prevents a firm conclusion being made. It is possible, but again not conclusive, that there is an association between HLA-DR4 and the symmetrical seronegative pattern of peripheral PsA. It is also likely that genes outwith the MHC predispose to psoriasis and PsA. It is further likely that a role will be found for environmental factors in both psoriasis and PsA. There is a tantalizing possibility of a complex interplay between a variety of environmental factors and genetic factors, both within and outwith the MHC, determining not only susceptibility but also the individual clinical pattern of disease. Further clarification of these possibilities is likely to depend primarily on understanding the role of genes within the MHC in predisposing to comparatively more homogeneous diseases, such as psoriasis and ankylosing spondylitis, before the mechanisms operating in PsA can be analysed and better understood.

Psoriatic arthritis was first described in the early part of the nineteenth century. Over the past 50 years, concepts of the disease have evolved as a result of clinical, epidemiological, radiological and immunogenetic study. Epidemiological and clinical investigations suggest that the disease is a unique arthropathy rather than the coincident occurrence of two common diseases. There are no validated criteria for classification; this is partly because of the heterogeneous clinical features associated with the disease, and the relapsing and remitting nature of both psoriasis and arthritis. Clinical subgroups have been proposed and have proved useful in study of the disease; however, there are inconsistencies and overlaps in the published data. The population prevalence of psoriatic arthritis is in the range of 2-10 per 10,000 although this is probably an underestimate as those with sacroiliac involvement only are not included. There are currently no incidence figures from population samples. The disease is slightly more common in females than males, although there is variation in the sex ratio by disease subgroup. There is evidence that hormonal and environmental factors play a role in the occurrence of disease.

1. Normal joints in individuals of all ages may tolerate prolonged and vigorous exercise without adverse consequences or accelerated development of OA. 2. Individuals who have underlying muscle weakness or imbalance, neurological abnormalities, anatomical variances, and who engage in significant amounts of exercise that stress the lower extremities, may accelerate the development of OA. 3. Individuals who have suffered injuries to supporting structures may also be susceptible to accelerated development of OA in weight-bearing joints, even without increased stress to the joint from exercise. 4. Certain individuals with established degenerative or inflammatory arthritis may benefit from supervised exercise programmes. 5. Still more information is needed so that physicians can identify subjects at risk for the development of OA, advise the millions of participants about the beneficial and deleterious effects of regular exercise and sports participation, and develop successful rehabilitation programmes for injured joints.

Physical activity epidemiological studies provide one of many types of research evidence that are necessary to assess the importance of physical activity to health. Available epidemiological evidence, when coupled with relevant experimental and clinical research, suggests that physical activity has the potential to favourably influence the development and progression of a variety of chronic diseases and conditions that are a burden to public health. The evidence is only beginning to emerge for elderly populations, however, thereby highlighting an important void in our scientific knowledge. Attempting to increase the level of physical activity of elderly people raises three important issues. First, improving adherence to a physically active life-style requires assistance of behavioural scientists, either through direct intervention, or through research that can help the elderly identify and overcome impediments to physical activity. Second, many elderly people have diseases that can limit their physical ability, but exercise scientists can assist by prescribing exercise that is both efficacious and safe given the level of limitation. Third, the number of injuries may increase with increased physical activity in elderly persons. Epidemiologists and exercise scientists working in the area of injury control can determine which activities are safe at specific levels of physical ability and function. To quote one of the originators of exercise physiology, Per Olaf Astrand (1992), 'As a consequence of diminished exercise tolerance, a large and increasing number of elderly people will be living below, at, or just above "thresholds" of physical ability, needing only a minor intercurrent illness to render them completely dependent'. Physical activity can help to push back that 'threshold of physical ability' and thereby improve physical functioning. As physical function improves, there is a propensity to perform even greater amounts of physical activity that may be essential to the quality and perhaps quantity of life for an elderly person.

Occupational physical activities over many years can induce osteoarthritis in selected joints. Well-studied examples include evidence of osteoarthritis of the knees and spine in miners, osteoarthritis of the hip in farmers and increased rates of osteoarthritis of otherwise not usually affected upper extremity joints in pneumatic drill operators. Occupation-induced osteoarthritis may not be limited to these uncommon occupations but may, in fact, account for a large proportion of osteoarthritis in the population. Additional studies of this issue, which incorporate high-quality ergonomic assessments of occupational physical activities, are needed. People with pre-existing arthritis often experience work disability, especially when faced with physically demanding jobs in which they have little control over the pace or the specific physical demands of their labour.

The data presented here document that exercise is associated with changes in immunological activity as assessed by a variety of in vitro assays. In general, these changes appear to be temporally associated with activity and are not persistent. In fact, most alterations are probably secondary to exercise-induced hormonal changes, with resultant effects on the intravascular composition of immunocompetent cells. Thus, changes in lymphocyte trafficking induced by hormonal effects lead to relative and absolute differences in cell numbers, which may be reflected in in vitro functional assays. These data argue against any profound impact of exercise on the immune system, which might impact on overall health. Furthermore, there is little information about exercise decreasing the number of infectious illnesses or diminishing the likelihood of immunologically mediated conditions or malignancies. Nevertheless, these results should not be construed as an argument against the tangible health benefits of exercise. The changes in life-style which often accompany exercise programmes, as well as the documented benefits for cardiovascular health, are reasons enough to support these activities.

Exercise testing is now widely used as both a diagnostic tool in the elderly and as a means of generating the information necessary to provide them with a valid exercise training prescription. An appropriate medical history and physical examination prior to exercise testing will allow for the adequate assessment of an individual's risk of undergoing an exercise test. Appropriate screening of the individual, assessment of risk prior to exercise, and appropriate monitoring during and following the exercise test have contributed to the relative safety of maximal exercise testing, with statistics indicating roughly one death occurs in every 10,000 clinical maximal exercise tests. When designing an exercise test protocol for use in the elderly, their reduced exercise capacities, increased prevalence of CV disease, and the reason for doing the test must be taken into consideration. The Bruce treadmill protocol is the most widely used exercise test in populations of all ages; however, because of its relatively high VO2 demands in the initial minutes of exercise, it may not be the optimal protocol for the elderly. Other alternative protocols including the Naughton and Balke tests may be more appropriate, especially when attempting to generate a valid exercise prescription. However, the modified Balke protocol, with a constant speed of 2 miles/h and starting on the level, is probably the best protocol for exercise testing in the elderly for the purposes of generating an exercise prescription. If individuals are unable to undergo exercise tests on a treadmill, cycle and arm ergometer tests provide alternative test modalities, but these have a number of inherent problems that must be considered prior to exercise testing. The interpretation of an elderly individual's ECG responses during a maximal exercise test is intimately related to their risk of having CV disease prior to the exercise test, though fewer false-positive tests will be evident because of the increased prevalence of CV disease in the elderly.

The number of women of all ages participating in physical activity is consistently increasing. Although there are numerous benefits to physical activity, specific problems may occur along the various stages of the female athlete's life, which need special attention. A remarkably late menarche, exaggerated beyond the expected genetic predisposition and a high prevalence of abnormal or absent menstrual cycles is seen in athletes, especially in dancers and long distance runners. Reproductive system dysfunction is associated with multiple factors, of which nutritional intake and caloric balance seem to be of a special importance. A high proportion of athletes suffer from pathological eating behaviours and there is an overlap between many features of anorexic patients and highly active athletes. The pathophysiology seen in most cases is hypo-oestrogenism due to suppression of the GnRH pulse generator. The mechanism(s) causing this reversible hypothalamic dysfunction are yet unknown. Of major concern are the skeletal abnormalities, including failure to reach peak bone mass, reduced bone density, scoliosis and stress fractures as a result of prolonged hypo-oestrogenism. Hormone replacement may be indicated in cases in which reduction of exercise or weight gain is not feasible or unsuccessful. Other populations that need special precautions are pregnant athletes and older women.

As 90% of patients with acute LBP recover within a 2-month period, irrespective of the type of treatment received, exercise probably plays little role in facilitating recovery from an acute episode of LBP. It may be a very important factor in both symptomatic and functional recovery in chronic LBP, as well as an integral factor in preventing recurrent injury. The most efficacious exercise regimen for treating LBP is currently unknown. Similarly, little is known about the efficacy of individual exercises. In certain patients, flexion or extension exercises may be inappropriate. A careful history and physical examination, observing the movements that cause pain, will assist the physician in tailoring the exercise programme to the individual patient to achieve the greatest likelihood of success. Communication between the patient, physician and therapist is vital to allow continual adjustment of the programme to best meet the patient's needs. As improvement occurs, more stressful exercises can be added to improve strength, endurance and aerobic fitness. Individualizing the exercise programme to the patient's symptoms and communication between the patient, therapist and physician lead to greater compliance with the exercise programme and a greater likelihood of improved outcome.

The data available indicate that ROM, strengthening and aerobic conditioning exercises are safe for patients with OA, RA or AS, despite earlier concerns that exercise might exacerbate joint symptoms or accelerate disease. Less clear are the therapeutic benefits of exercise. In patients with OA, stretching, strengthening, and aerobic conditioning programmes can improve the deficits observed in these patients. The improvements observed generally have been small, and the evidence that these individual improvements result in improved overall function is minimal. None the less, it is likely that exercise will reduce pain, improve endurance for physical activities and improve cardiovascular fitness. Study of the long-term effects of exercise in the geriatric population, for sustaining independent living and functioning, is critically important for future health care and social expenditures. In RA, strengthening and aerobic conditioning exercise programmes can increase muscle strength and cardiovascular fitness and probably improve physical function as well. Improvements demonstrated in patients with RA seem more convincing than those in patients with OA and AS; this probably represents their poorer physical status prior to exercising. For patients with AS, intensive physiotherapy brings statistically significant short-term improvements in spinal and hip ROM which are only modestly clinically significant. It is possible that spinal mobility exercises decelerate loss of mobility over the long term, but controlled studies are needed to confirm this. Improvement in respiratory function with exercise appears to be related to cardiopulmonary fitness and perhaps to improvements in diaphragmatic respiration rather than to changes in thoracic cage mobility. Given the overall safety and likely benefits of the described forms of exercise, exercise should be included in the overall treatment of patients with OA, RA or AS. Careful patient evaluation and education about exercise should be a part of the exercise programme.

Once the almost exclusive domain of the orthopaedic surgeon, sports injuries are now being seen with increasing frequency by other specialists, including rheumatologists. It is therefore important for rheumatologists to be able to diagnose and manage the various musculoskeletal conditions that are associated with physical activity. Soft tissue injuries are a very common cause of morbidity in both competitive and recreational athletes. Most of these conditions are provoked by muscle-tendon overload (or overuse) that is usually the result of excessive training or improper training techniques. However, despite an emerging literature on the natural history of soft tissue overuse syndromes, relatively little is known about the causes, incidence and outcome of many of these injuries. Of the methodologically robust epidemiological studies that have been done, most have focused on habitual distance runners. In this population, it has been reported that the incidence of injury can be as high as 50% or more, and that overtraining and the presence of previous injury are the most significant predictors of future injury. In other popular forms of exercise, such as walking, swimming, cycling, aerobics and racquet sports, injuries are also reported with high frequency but, to date, no prospective studies have examined actual incidences in these populations, and risk factors for injury in these activities remain speculative. Several of the more commonly occurring soft tissue injuries (such as rotator cuff tendinitis, lateral and medial epicondylitis, patellar tendinitis, the iliotibial band friction syndrome, Achilles tendinitis and plantar fasciitis) exemplify the overuse concept and are therefore highlighted in this review. The management of these, and most other, exercise-related soft tissue injuries is directed towards promptly restoring normal function and preventing re-injury.

We have reviewed the frequency and variety of rheumatic problems among performing artists. For instrumentalists, injuries are related to the type of instrument played, the technique used and the effort expended in the quest for excellence. For dancers, musculoskeletal problems too reflect technique and effort. We should not be surprised at the frequency of these problems. Rheumatologists, as well as orthopaedic surgeons, physiotherapists, neurologists and other physicians, encounter performing artists as patients. We should be familiar with their problems and be able to knowledgeably diagnose and manage them. This may include observing the artist during actual performances. How is the instrument being held? What is the posture of the artist? What are the comments of the coach or teacher. What type of shoes does the ballerina wear? What movements in particular cause discomfort? These and similar observations will have direct bearing on the musculoskeletal problems of these artists. Published studies have related the variety, frequency and disabling nature of performance-related musculoskeletal problems. Unfortunately few if any of these are controlled, blinded or prospective. We need more and better information. We will want clear information about prevalence of problems, better definition of the musculoskeletal ailments, classification of the relationship of problems with performance and individual biomechanical features, information about response of specific problems to interventions, and data about the long-term consequences, if any, of these rheumatic problems to the musculoskeletal system. Artists as patients are unique. Minor problems can become potentially career-ending disabilities. Making music or performing dance may provide us with delightful entertainment but represents a source of livelihood to artists. Understanding their medical needs and enabling them to continue to perform is the challenge before us.