recent study of 48 women with pSS, there was an inverse relationship between diastolic blood pressure and fatigue levels [20]. The hypothesis is that autonomic dysfunction predisposes to lower blood pressure and this in turn may predispose to increased fatigue levels. Again this needs to be investigated in larger groups of patients and with more detailed studies before this can be regarded as deÞnitive.

21.3.1.3 Sleep

Lack of sleep is a potential biological cause of fatigue. It would be logical, therefore, to hypothesize that oral dryness in particular might lead to increased waking at night and therefore disturbed sleep and hence fatigue. Another possibility is that drinking water before bed to reduce dryness symptoms might lead to waking up at night to pass urine. There are studies in pSS investigating sleep disturbance. These include a study of 65 patients (predating the AmericanÐEuropean consensus criteria) demonstrating severe sleep disturbance in 75% using a 10-item Mini Sleep Questionnaire, but no relationship with clinical or laboratory parameters [21]. In this study, 55% of these patients were regarded as also having Þbromyalgia (see below), which may suggest the involvement of psychosocial factors rather than pure biological ones. In another questionnairebased study of 40 patients, sleep disturbance was more common than in comparator groups of controls or RA patients, as was fatigue [22]. At least in terms of difÞculty in falling asleep the reported issues were muscular tension and restless legs, however, rather than dryness symptoms. In another study of 76 patients sleep disturbance assessed by the Epworth Sleepiness Scale was commoner in pSS than in patients with osteoarthritis even though there was no difference in fatigue measured by the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) scale [23]. This study was focused on urinary symptoms as a potential marker of antimuscarinic antibody-related autonomic dysfunction and found a correlation between urological symptoms and daytime sleepiness.

These studies did not focus on the possible relationships between sleepiness and sicca

symptoms and this is an area still to be studied in detail. In addition, these studies assessed sleep using questionnaires and it would be of particular interest to compare these data with objective measures of sleep such as polysomnography.

21.3.2 Psychosocial

21.3.2.1 Depression

Valtysdottir et al. identiÞed higher levels of depression in 62 pSS patients than in 38 RA patients or 63 healthy controls using the Hospital Anxiety And Depression Scale (HADS) [24], although the Þnding of similar depression scores for RA patients and healthy controls in this study differs from other studies in which RA is associated with an increased prevalence of low mood [25]. Nevertheless, another study of 40 patients with pSS using the HADS also showed a higher prevalence of clinical depression risk compared with controls [26]. In a study of 49 pSS patients, correlations were found between depression measured by the Zung depression scale and dimensions of reduced motivation and mental fatigue measured by the Multidimensional Fatigue Inventory (MFI) [3]. In our patients with pSS there was a similar prevalence of low mood to that in patients with RA and SLE, which was greater than in matched controls [2]. Furthermore, when anxiety and depression (measured by the HADS) were controlled, the differences between patient groups and controls were largely maintained. We did not identify any signiÞcant correlations between fatigue or pain and the HADS, i.e., the fatigue levels identiÞed could not be accounted for by levels of depression. In another study of 111 patients with pSS, fatigue and pain correlated with quality of life and psychological distress [27]. One issue to be aware of is that some of the questions in depression or anxiety scales can reßect features of the disease (e.g., dry mouth as a feature of anxiety). The scores from such a questionnaire may overestimate the prevalence of anxiety or depressionÑso-called criterion contamination [25].

What these studies show, overall, is an increased prevalence of depressive/low mood