Currently there are no laboratory markers that correlate well with the clinical findings in BD. Therefore assessment of disease activity has to be based on history of clinical features. There have been several attempts to develop disease activity measurements: (1) the scheme in use by H Yazici (1984; evaluation depends on features found on the day the patient attends clinic); (2) the Iranian Behçet's disease Dynamic Measure (IBDDAM; F Davatchi 1991; evaluation depends on accurate history of symptoms up to 12 months prior to the date of assessment); and (3) the European scheme (1991; initially developed in the UK by Chamberlain-Barnes-Silman incorporating features of the scheme used by H Yazici). In all three forms scoring of disease activity is based on clinical features only.

In 1994 a workshop was held in Leeds (UK) to arrive at a consensus view about the contents of the activity form with emphasis on the need for clarity and consistency for potential use by clinicians worldwide. The Behçet's Disease Current Activity Form (BDCAF) was developed, which depends on accurate history of clinical features present during the month prior to the date of assessment. Clinical features in BD vary considerably over time; in order to document this variation, new clinical features present over the preceding 28 days are scored. This represents a compromise between assessing disease activity based on clinical features on day of assessment, which may be unrepresentative of overall disease activity and clinical features present over a longer time period, as in the IBDDAM, which reduces reliability in terms of accurate recall of symptoms by patients. In BDCAF disease activity rating for oral and genital ulceration, and skin lesions relies solely on the duration of symptoms and does not take into account the size or number of lesions present (which might also reflect activity).

A study from Bhakta BB et al. (Rheumatology 1999) shows that the BDCAF is easy to complete and is a reliable method of assessing and documenting clinical activity in BD patients for use in routine clinical practice, that it has a good interobserver reliability for general disease activity and that there is difficulty in reliable scoring of uncommon manifestations such as large vessel involvement, GI inflammation and nervous system involvement.

A Turkish study (Hamuryudan et al., Rheumatology 1999) to examine interobserver and intraobserver reliability of the Turkish version of BDCAF shows a good intra- and interobserver agreement for orogenital ulcers and eye involvement, a poor agreement between and within observers for their overall impression and individual low kappa scores for erythema nodosum, vascular, CNS and gastrointestinal involvement. A local disease activity index (Lee ES et al., Book of Abstracts, 10th International Congress on Behçet's disease, Berlin, 2002) was developed by Koreans that attempted to overcome cultural differences. It also excludes any terms that could be biased, such as fatigue or headache.

For the future we propose a setting of a general clinical score, an organ specific clinical score, laboratory assessments and imaging techniques (like MR for CNS involvement, CT/MR-angiogram, ¹⁸F-FDG-PET for vasculitis, etc.), which enables us to distinguish between chronic or degenerative changes and active lesions whenever possible. Disease related overall damage would be the total of the cumulative old damage and the damage by active disease.