Exploration of Confounding Due to Poor Health in an Accelerometer-Mortality Study.

PURPOSE: Confounding due to poor health is a concern in accelerometer-based studies of physical activity and health, but detailed investigations of this source of bias are lacking. METHODS: US adults (n = 4840) from the National Health and Nutrition Examination Survey (2003 to 2006) wore an accelerometer for 1 to 7 d (mean = 5.7 d) and were followed for mortality through 2015. Logistic regression was used to examine odds ratios between poor health (chronic conditions, self-reported health, mobility limitations, frailty) and low physical activity levels; Cox models were used to estimate adjusted hazard ratios (HR) and 95% CI for mortality associations for a 1 h·d increase in moderate-to-vigorous-intensity physical activity (MVPA) using two commonly used cut-points (MVPA760, MVPA2020). Modeling scenarios with shorter and longer follow-up time, increasing adjustment for poor health, by age group, and after excluding early years of follow-up were used to assess bias. RESULTS: Over a mean of 10.1 yr of follow-up, 1165 deaths occurred. Poor health was associated with low MVPA760 levels and increased mortality risk. In fully adjusted MVPA760 models, HR was 26% stronger comparing 0 to 4 yr (HR = 0.46) with 0 to 12 yr of follow-up (HR = 0.62), particularly in older adults (65 yr and older). Increasing statistical adjustment for poor health attenuated MVPA760 associations by 13% to 15%, and exclusion of the first 2 yr of follow-up had limited effects. Comparable results were obtained with the MVPA2020 cut-point. CONCLUSIONS: We did not find evidence that confounding by health status resulted in entirely spurious MVPA-mortality associations; however, potential bias was appreciable in modeling scenarios involving shorter follow-up (<6 yr), older adults, and more limited statistical adjustment for poor health. The strength of MVPA-mortality associations in studies reflecting these scenarios should be interpreted cautiously.

A fitting tribute to Epilepsia partialis continua.

In July 2014, a 66 year-old lady presented to emergency department after having not been seen for 3 days. She was eventually found in bed not responding verbally. The ambulance service reported tonic-clonic seizures lasting 10-30 s every 3 min. The patient was treated for her seizures with phenytoin and additional benzodiazepines as required. Her seizure had temporarily resolved and she was admitted for investigations. She had no history of epilepsy or seizures. The history of alcoholism and lack of any substantial history of epilepsy, left the team considering whether this was an alcohol induced event or a pseudoseizure. The patient referred to no prodrome, no tongue biting/incontinence and lacked any convincing post-ictal phases. The seizures were no longer tonic-clonic but evolved into focal motor, with right-sided facial twitching lasting 2 min. Her investigations from bloods, lumbar puncture, computerised tomography scan and magnetic resonance imaging were all normal which led the team to consider whether this was a pseudoseizure. The patient appeared unconscious during seizures but was rousable during the episodes, although she claimed to have no recollection of them after. The seizures frequency settled at 30/day after being resistant to most antiepileptic regimes, except the eventual combination of Levetiracetam 1000 mg BD and Sodium Valproate 400 mg which left her seizure-free. However, the key evidence separating pseudoseizures and epilepsy partialis continua lay in collecting video evidence. This rare but important differential can often be overlooked but is especially important in the elderly, in whom this condition can mask serious underlying pathology.