The natural history of flare-ups: a daily diary study of patients with, or at high risk of, knee osteoarthritis

Abstract

Purpose: To determine, in a sample of community dwelling adults, the natural history of flare-ups in knee osteoarthritis (OA). Methods: 330 adults aged 45 years and over with a recent primary care consultation for knee OA/arthralgia and no existing diagnosis of inflammatory disease were invited to complete a daily pen-and-paper diary for up to 3 months. Average knee pain intensity in the past 24 hours (0-10NRS) was rated daily, along with pain quality, other symptoms, and interference with usual activities. Informed by a systematic review of the literature, flare-ups were defined as an increase in pain intensity of a minimum of 2 points above participants’ rating of their usual pain intensity, sustained for a minimum of 2 consecutive days (i.e. excluding more transient episodes of pain). A flare-up was judged ‘resolved’ when pain intensity returned to usual levels for at least 5 consecutive days. We calculated the rate of flare-ups in the sample as an incidence density per 100 person-days at risk and used descriptive statistics and plots to summarise duration and nature of flare-ups. Results: 67 participants (mean age 62.2 (SD 10.6); 55% female) completed at least one month of diaries. 30 participants experienced a total of 54 flare-ups (incidence density 1.09 flare-ups per 100 person-days). On average, flare-ups showed reductions in pain within 2 days followed by a longer, gradual return to ‘usual’ pain intensity (Fig. 1). The pattern differed between individuals with the median time to resolution = 8 days (range: 2-30). During a flare-up participants were more likely to report several additional features compared to days when they were not in a flare: swelling (50% vs 35%), limping (64% vs 42%), stiffness (60% vs 26%), night pain (34% vs 10%). On a third of flare-up days, patients increased their pain medication. Despite this, on 15% of flare-up days, pain stopped usual activities. Conclusions: Our small study with intensive longitudinal data collection suggests acute flare-ups may be experienced by a substantial number of patients. These episodes often last a week or longer, interfere with sleep and daily activities, and lead to increased analgesic use.