The nomenclature and classification criteria for arthritis in children should be dealt with initially as separate issues, although they are undoubtedly intertwined. The classification criteria should aim to delineate homogeneous patient populations, yet should be flexible enough to incorporate advances in disease knowledge. It should be recognized that arriving at an international consensus for classification criteria will merely provide a set of operational definitions to facilitate research, and not a set of diagnostic criteria. Indeed the only point to obtaining consensus is to begin a process of systematic ongoing review of the criteria. The labels attached to any of these diseases should facilitate accurate communication. In view of the heterogeneous nature of childhood arthritis, consideration should be given to using a broad umbrella term such as juvenile or childhood arthritis only for communicating with the lay public. Medical nomenclature should be formulated to reflect accurately homogeneous subgroups of arthritis, and should not artificially proscribe a relationship between paediatric and adult disease.

Despite the fact that psoriatic arthritis has been recognized as an entity for almost five decades, there are still no valid criteria for either its diagnosis or classification. Several sets of criteria have been proposed but none was studied. None the less, investigators have been able to study the condition and describe its unique features and its natural course and prognosis. However, in order to facilitate further studies, it would be worthwhile to develop an internationally accepted and validated set of criteria, both for the diagnosis and classification of the disease, as well as for the assessment of damage. These criteria would help set up appropriate therapeutic trials in this condition as well.

Disease activity in rheumatoid arthritis is not easily measured. The validity of current measures has been reviewed. Recent international efforts have resulted in consensus over a minimum (WHO/ILAR) core set of endpoints in RA trials: pain, patient and physician (assessor) global assessment, physical disability, swollen joint count, tender joint count, acute phase reactants; and for studies of one or more years' duration: radiographs of joints. The near future will hopefully see validation of new measures, also in terrains not currently covered by the core set.

The development of classification schemes for RA in the last 40 years has followed the increasingly precise understanding of the nature of the clinical disease and the recognition of the different requirements of classification methods in clinic and population settings. In published studies of RA in clinic patients the most widely used criteria sets have been the 1958 ARA (ACR) criteria and its 1961 adaptation (the Rome (active) criteria). These sets classified disease as 'classical', 'definite', 'probable' and 'possible' RA based on criteria comprising clinical, serological, radiological and histological features (the latter were dropped from the Rome criteria set because of their impracticality). More recently, a new criteria set (the 1987 ARA criteria) has been developed using statistical techniques. This set was derived using RA cases and controls attending hospital clinics. It is based on the earlier criteria sets but accommodates the characteristic pattern of joint involvement in RA more precisely. The criteria recognize only the single disease category of 'rheumatoid arthritis'. In validation studies, the 1987 criteria set has been found to have enhanced specificity over earlier schemes in clinic-based studies of RA. The sensitivity may, however, be reduced, in particular in studies of early disease. The application of classification criteria for case recognition in the population and family studies of RA has proved more problematic. In these settings, there is the additional requirement to recognize individuals with remitted and inactive disease as RA cases. The 1966 New York criteria were developed for this specific purpose, however their format proved cumbersome and they have not been widely adopted. The 1987 criteria set is insufficiently sensitive to recognize inactive disease if the criteria are applied exactly as they have been defined. The sensitivity of the 1987 criteria set is, however, substantially enhanced if the criteria are adapted to incorporate features of past disease activity, for example by allowing deformity to substitute for swelling and by incorporating data on the past occurrence of rheumatoid factor and rheumatoid nodules. Developments in the immunology and genetics of RA may in the future provide more accurate tools for classification and may lead to recognition of more precise disease subsets. At present, however, the 1987 ARA criteria provide the most appropriate basis for case recognition in both clinic and population-based studies.

The methodology for developing and assessing disease status measures is now well-advanced. For some diseases, in particular SLE and RA, these methods have been applied and instruments either are being or have been validated. For other conditions, such as ankylosing spondylitis and Behçet's disease, there is still a need for reliable measures to be proposed and evaluated.

We have discussed methodological and statistical considerations in developing disease classification and assessment criteria. In choosing cases with disease and nondisease controls, classification criteria should be developed with an eye toward face, content and construct validity, and toward their ultimate applicability. The validity of disease criteria should be tested in a patient sample different from the one used to develop the criteria. Several analytic approaches are available to reduce the candidate diagnostic elements to those that will define the presence of disease. Methodological issues in the assessment of disease severity, activity or damage are similar to those faced in criteria development studies, although the analytic concerns are different and the options more varied.

The spondyloarthropathies occur with variable frequency in the tropics. Ankylosing spondylitis, in particular, is thought to be rare in tropical Africa, reflecting a low frequency of the HLA B27 gene. However, in the Melanesian populations of Papua New Guinea where there is a relatively high frequency of HLA B27, ankylosing spondylosis is infrequent. These diverse observations may be related to variations in B27 sub-types. Reactive arthritis is a common and important form of acute arthritis in the tropics and in Papua New Guinea at least has a strong association with HLA B27. In Africa an increasing prevalence of reactive arthritis may be related to the spread of HIV infection. Extra-articular features such as balanitis and enthositis are helpful pointers to the diagnosis. Disseminated gonococcal infection and tuberculosis must always be considered and treatment offered if doubt exists. The mainstay of treatment of reactive arthritis is, as always, an anti-inflammatory drug, supplemented by hydrocortisone injections; docycline is available for chlamydia-triggered arthritis and chloroquine or dapsone for more chronic, unresponsive cases.

We have recounted the remarkable story of gout and hyperuricaemia in the indigenous populations of the Pacific and noted the recent identification of the same problem in communities in rural Indonesia. Gout is increasingly recognized in African populations, especially in urban centres. There is no doubt that gout is 'alive and well' and presents a continuing challenge to future generations in developing countries.

The presence of excessive quantities of fluorine in drinking water is accompanied by a characteristic sequence of changes in teeth, bone and periarticular tissues. These changes lead to a variable degree of locomotor disability, ranging from simple mechanical back pain to severe, crippling, combined locomotor and neurological impairment. In endemic areas, a substantial proportion of the population may be affected, posing a severe public health problem. In some areas, the hazards to human health are not fully appreciated and are under-reported. The maximum impact is felt in those communities engaged in physically strenuous activities, either agricultural or industrial. The need of these often isolated communities in economically hard-pressed countries, for the provision of low-fluoride drinking water remains a hope rather than an expectation at the present time.

There are few studies on the prevalence, pattern or clinical course of osteoarthritis (OA) in the tropics. The studies that have been carried out, however, indicate that on the whole there is a lower prevalence of OA than found in Western countries. In addition, the pattern of joint involvement may be different with less common involvement of the hip relative to the knee and polyarticular OA is uncommon in many parts of the tropics. It also seems likely that a significant number of these patients in the tropics have OA secondary to various infections including pyogenic, tuberculous and parasitic infections. There is an urgent need to confirm these observations and to identify possible genetic, developmental or environmental factors influencing the expression of OA in the tropics. In addition degenerative arthropathies, such as Mseleni's disease, present in some parts of the tropics, merit further study. With increasing life-expectancy and improved health-care in many parts of the tropics, OA will become an increasingly prevalent and important condition with associated morbidity and socio-economic implications for these countries.

That juvenile chronic arthritis (JCA) occurs in tropical countries there is no doubt. The spectrum of differential diagnoses is wider than in temperate regions. The disease tends to be more severe irrespective of the type of onset, and there is a high incidence of positive rheumatoid factor. Many cases present with advanced disease. There is a need for the establishment of clinics devoted specifically to the detection, documentation, and treatment of JCA.

With a few exceptions, there remains a paucity of good epidemiological studies from India and South-East Asia. The overall impression is that the prevalence of rheumatoid arthritis (RA) is slightly less compared with the West and follows a milder course. There may be differences in the articular expression of the disease with the wrist and forefoot less commonly affected than in Caucasian studies. Extra-articular manifestations and erosive change are less frequent and severe. HLA DR4 does not correlate with seropositivity and severity of RA. The prevalence of SLE may be less in the Indian subcontinent than in the West. However, recent indications are that in South-East Asia and the Pacific region the prevalence morbidity and mortality are higher than in developed countries. An improvement in socio-economic conditions may be accompanied by an improvement in the survival of patients with SLE.

Rheumatoid arthritis (RA) once a rarity in Africa, is now reported in large numbers from many parts of Africa. Although epidemiological surveys have shown that the prevalence in urban populations is similar to Western communities, it is less common in rural areas. Further epidemiological studies are needed to confirm these findings in other parts of Africa and identify factors contributing to this difference to provide a better understanding for the emergence of RA in Africa. Earlier reports suggested that in African blacks RA was a mild disease, severe radiographic changes were uncommon, deformities were rare and extra-articular features were unusual and only symptomatic therapy was necessary to control symptoms in most patients. Recent experience shows that severe disease with deformities and radiographic changes are seen and a wide spectrum of extra-articular features are noted although they may be less common than in Caucasians. African blacks with RA may have a younger age of onset and the genetic association with HLA DR4 has been confirmed. Systemic lupus erythematosus (SLE) is also recognized more often in African blacks who have a younger age of onset. SLE is also recognized less often in males. Features such as photosensitivity and serositis are less common while renal disease is more common. A reported short-term mortality of about 30% emphasizes the need for urgent efforts to improve the prognosis in SLE. The infrequent occurrence of localized systemic sclerosis and the absence of anti-centromere antibodies in blacks was noted in a recent large series of patients with systemic sclerosis. The other connective tissue diseases and systemic vasculitides are reported much less frequently and will probably be detected more often in future. Anti-cardiolipin antibodies are detected frequently in association with infections, including HIV infection. The spectrum of diseases associated with ANCA includes a variety of connective tissue diseases and infections such as HIV infection and invasive amoebiasis must be added.

The presence of auto-antibodies in infectious diseases continues to puzzle and provoke. It is hoped that sequencing studies in particular will yield further clues as to the role and mechanism of production of autoantibodies in infectious diseases. This, in turn, may also provide further insights into the role of auto-antibodies in auto-immune diseases. From a practical clinical viewpoint, the search for improved auto-antibody tests and new diagnostic markers with improved sensitivity and specificity must continue in the tropics. Until this is achieved, the results of auto-antibody tests in persons living in the tropics, persons from the tropics or patients with tropical infections, must be interpreted with caution.

There is still far too little information available on the rheumatic diseases in Africa. Epidemiological studies are required in order to determine the burden of illness from rheumatic diseases on the African continent as well as to identify local risk factors for certain diseases. Such studies will also serve to enable the development of preventative and rehabilitation strategies. Functional disability has to be assessed in relation to the prevailing sociocultural lifestyle on the continent. Measures of disability that reflect this await development whilst regional diagnostic criteria also need to be worked out. The validity of tests and the stability of test reagents in a tropical climate require analysis. Continuing assessment of rheumatological services is essential to ensure their effectiveness and efficiency in the community and in particular to determine health care priorities and the best forms of therapeutic intervention. This will enable judicious use of limited resources. Community surveys in Africa are fraught with constraints and are difficult to undertake owing to a shortage of manpower and financial resources. For this reason, most studies hitherto have been hospital based. Hospital studies though useful lack applicability to the population as a whole and consequently more emphasis on cross-sectional and longitudinal community studies are required. It is hoped that despite the restraints, these studies will be performed.

A variety of musculoskeletal syndromes has been described in association with numerous parasitic infestations. Arthritis, enthesitis, myositis and vasculitis have been described in infected individuals resident in, or visitors to, endemic areas. The diagnosis of parasitic rheumatism is supported by poor response to anti-inflammatory drugs and improvement following antiparasitic treatment.

Staphylococcal pyomyositis is an important and common condition in many areas in the tropics. The cause is probably multifactorial and includes damage to the skeletal muscle in the presence of staphylococcal bacteraemia, with or without depressed immunity. In Africa, there are indications of an increased prevalence in association with HIV infection in young adults in whom multiple and recurrent abscesses are common. Long bone osteomyelitis is an important differential diagnosis in these patients. Timely surgical drainage and antibiotics leads to resolution. Delayed diagnosis is associated with disseminated disease and septic cardiorespiratory complications.

Arthritis is a common feature of leprosy and contributes to disability. Direct invasion of joints and bones by mycobacteria may lead to a destructive arthritis in lepromatous disease. The infective process may involve few or many joints. Reactional states may occur spontaneously but usually after the initiation of anti-mycobacterial treatment. In both the type 1 reaction of borderline case and the type 2 reaction of the lepromatous disease, intense inflammation may occur at sites of infection. The immunology of the reactions is different but they share clinical features including a polyarthritis which may resemble rheumatoid disease. The joint disease may be chronic or relapsing, affecting the wrists and small joints of the hands in particular. Radiological erosions may occur. Mycobacterium leprae is not found in the synovium in this pattern of arthritis. Further study of this phenomenon might yield useful information above the mechanism of joint inflammation in other rheumatic diseases.

Osteoarticular brucellosis has been documented extensively from the Middle East and Spain in the last 5 years, but it has only been reported infrequently from the UK and USA. Brucella melitensis from goat and sheep is the most frequently isolated organism. Peripheral articular pain, particularly of the large joints, is the commonest osteoarticular manifestation, while effusions that seldom yield organisms on culture, also occur frequently. Sacroiliitis which most frequently is unilateral, often presents acutely and dramatically with severe pain that is poorly localized to the lower back and buttock, leading to difficulty in walking and even standing. Tapping the heel and springing the sacrum is probably the best way of localizing the pain to the sacroiliac joint in this acute stage. Lack of awareness of this pattern of presentation could lead to misdiagnosis. Spondylitis is the third major manifestation of osteoarticular brucellosis. It occurs in older patients and is insidious and chronic in onset and course. The lumbar spine is most frequently involved, although cervical involvement is frequently associated with more complications, particularly compressive neurological deficits. Osteomyelitis occurs unusually. Several large series have been reported among children. In them peripheral large joint involvement in association with systemic features predominate while sacroiliitis may occur unusually. Plain X-rays often demonstrate vertebral damage, involving the upper anterior margin most frequently. CT scans define better vertebral damage that is characterized by bony sclerosis and the less frequently encountered extradural extension and para-vertebral abscess formation. Technetium bone scan is the most sensitive technique for detecting acute sacroiliitis and other sites of early osteoarticular involvement. A four-fold rise in Brucella agglutination titre is the most frequently utilized diagnostic aid. A 6 week culture in a CO2-enriched medium is recommended for growing Brucella. Tetracycline or doxycycline 200 mg per day for 6 weeks is the mainstay of most medical treatment schedules. Combination with streptomycin for 3 weeks or rifampicin for 6 weeks is recommended, to reduce significantly the failure and relapse rate. Spinal involvement is associated with an increased failure and relapse rate while they occurred least among those with no osteoarticular involvement. Surgical intervention to stabilize the spine and relieve neurological compression may become necessary. With the use of these various measures, the outlook for complete recovery is good.