Abstract
Summary In psoriatic arthritis, it is important to understand the joint activity (represented by swelling and pain) and damage processes because both are related to severe physical disability. The paper aims to provide a comprehensive investigation into both processes occurring over time, in particular their relationship, by specifying a joint multistate model at the individual hand joint level, which also accounts for many of their important features. As there are multiple hand joints, such an analysis will be based on the use of clustered multistate models. Here we consider an observation level random‐effects structure with dynamic covariates and allow for the possibility that a subpopulation of patients is at minimal risk of damage. Such an analysis is found to provide further understanding of the activity–damage relationship beyond that provided by previous analyses. Consideration is also given to the modelling of mean sojourn times and jump probabilities. In particular, a novel model parameterization which allows easily interpretable covariate effects to act on these quantities is proposed.
Highlights
Manifestations of the disease typically result in joints becoming swollen and/or painful, which are reversible through treatment or management strategies or spontaneously, and may lead to permanent joint damage
The binary variable specifying the presence of opposite joint damage is motivated by previous analyses (Cresswell and Farewell, 2011; O’Keeffe et al, 2011) which indicate evidence of symmetric joint damage; the propensity of damage for a joint in a specific location to become damaged is increased if the contralateral joint in the other hand is earlier damaged
Along with dynamic covariates, the presence of opposite joint damage, sex, age at onset of arthritis and duration of arthritis were included in the analysis, as before
Summary
Manifestations of the disease typically result in joints becoming swollen and/or painful (active joints), which are reversible through treatment or management strategies or spontaneously, and may lead to permanent joint damage. Among others, individual joint level three-state models consisting of a not-active and not-damaged state, active and not-damaged state and an absorbing damaged state were proposed and produced strong evidence of a greatly increased transition rate to damage when a joint is active (compared with a joint being not active). The purpose of this paper is to extend the current modelling framework so that greater confidence with regard to the association between activity and damage can be achieved, and to inform on other important clinical questions.
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