Primary SS is a chronic disease with diverse clinical presentations which often leads to delayed diagnosis. Neurological complications and other extraglandular manifestations may precede the occurrence of typical symptoms of dryness (35% of patients in our study group). Delays in the diagnosis of pSS may contribute not only to the psychological distress, but also delay in starting the proper therapy and, therefore, may cause the development of systemic complications. Previous studies have shown large discrepancies in the prevalence and clinical picture of the nervous system involvement in pSS patients. Our study has clearly shown that peripheral nervous involvement is frequent, but remains under diagnosed in pSS patients, and it is correlated with worse HR-QOL. Patients with peripheral nervous system involvement obtained significantly lower scores in five domains of the SF-36: role-physical, role-emotional, vitality, bodily pain, and general health. There is an agreement in the literature that HR-QOL is impaired in pSS, but so far, it has been reported to be associated with fatigue, pain, sicca symptoms, and psychological distress [4, 18,19,20].
Fatigue (expressed as reduced vitality in SF-36) and pain are the most common extraglandular symptoms reported by patients suffering from rheumatologic diseases [21,22,23]. In population-based studies, the prevalence of persistent fatigue reaches approximately 20% among healthy individuals and up to 70% in patients with autoimmune diseases [21, 22]. The pathogenesis of persistent fatigue is still unknown. The proven impact of fatigue on patients’ quality of life is of great importance. Fatigue has been associated with mood disturbances, decreased motivation, impaired sleep, chronic pain, inflammation, and psychosocial variables, which makes it one of the most comprehensive medical issues [22, 23].
The two items of bodily pain domain assess the frequency of pain and its impact on daily functioning, but does not distinguish the type of pain and its intensity. We suggest that additional evaluation of the intensity of pain according to VAS scale and using a semistructured interview to try to categorize the type of pain into neuropathic, muscular, or articular is vital in these patients’ group. Even if the pain is in the range of mild-to-moderate like in our group, it should be emphasized that we are considering chronic pain accompanying the patient every single day. Moreover, one should not assume that every pain suffered by a patient with a rheumatic disease is articular. According to clinicians’ assessment, many of our patients suffered from neuropathic pain. It should be emphasized that physician should strive to determine the nature of the pain and thus to start appropriate treatment.
It is interesting to mention that in our study, there was a noticeable difference between pain scores on VAS scale and ESSPRI index, although the correlation between these two indicators was statistically significant (r = 0.53). The median score of pain on VAS in PNS + compared to PNS − patients was 3 (range 0–7) and 0 (range 0–7), respectively, while median score of pain on ESSPRI in PNS + compared to PNS − patients was 5 (0–8) and 4 (0–8), respectively. The possible scores on both scales range from 0 to 10, and in both, the same period of time was taken into account (2 weeks prior to the assessment). Previous surveys have indicated that ESSPRI correlates significantly with other patient-reported scales including VAS-pain. However, the ESSPRI index does not distinguish the type of pain and rating together with other components (fatigue and dryness) may cause an overstatement of the pain score. We hypothesize that more extensive pain assessment scale should be used in this group of patients to eliminate the negative effects of other symptoms on pain scoring and to distinguish the type of pain which is predominant to adjust the proper treatment.
Among the rheumatic diseases, functional disability most often affects patients with rheumatoid arthritis (RA) and systemic sclerosis (SSc). SS patients tend to be overlooked in this manner, because their disease is not “externally noticeable” like joint deformations in RA or contractures in SSc. However, concomitant neuropathy can significantly affect physical functioning in pSS patients. The median ODSS score determining the severity of disability due to peripheral neuropathy in our study was 1 (0–7) in PNS + group which reflects the worse every day functioning and may explain the low scores in role-physical domain. In PNS + patients, the neurological examination most often revealed sensory deficits and mild-to-moderate muscle weakness. However, in one patient, ataxic sensory neuropathy led to a significant disability due to severe loss of proprioception and kinesthesia.
When a difficulty in performing certain activity occurs, many of the patients adapt by starting to choose alternative ones. Also in many of them, psychological adaptation occurs, because expectations are being reduced [4]. This may be the explanation why the three domains physical functioning, social functioning, and mental health did not differ statistically between the subgroups.
These two factors, i.e., neuropathic pain and disability due to neuropathy, may be two important components that affect the HR-QOL. Further research is needed in this field.
Scores on SF-36 obtained from PNS + SS patients in our study are similar to those previously obtained from RA patients [24]. However, in RA patients, the low scores in physical domains resulted predominantly from joint involvement. Compared to systemic lupus erythematosus (SLE) patients, SS patients with neuropathy report poorer HR-QOL; they tend to score lower in physical functioning, mental health, bodily pain, and general health domains [25].
PNS + SS patients tended to score lower in physical functioning, role-physical, bodily pain, vitality, and general health domains compared to systemic sclerosis (SSc) patients [7]. In SSc patients, disease duration, gastrointestinal, and pulmonary involvement were negatively correlated with SF-36 physical domains, and the extent of skin involvement (measured with modified Rodnan skin score) was associated with reduced both physical and mental scores.
SS patients in general tended to have lower scores in vitality domain than patients with RA, SLE, and SSc [7]. This is intriguing, because SS has the best prognosis regarding life expectancy when compared with the above-mentioned diseases. This “low vitality” may result from nonspecific multiorgan symptoms, delay in the diagnosis, disease advancement at the time of diagnosis, and insufficient diagnosis of extraglandular complications. Also unrecognized nature of chronic pain and hence inappropriate treatment may be responsible.
Development of medicine with extensive diagnostic options and new treatment possibilities has improved mean life expectancies, leading to an increased number of patients with chronic diseases [26, 27]. Deterioration in physical and psychosocial functioning associated with chronic diseases has a negative impact on patients’ HR-QOL. This obliges healthcare professionals to take a comprehensive assessment of patients with consideration of both the disease activity and the patient-reported outcomes. Only this comprehensive approach could enable adjusting proper personalized treatment strategy working toward improving patients’ functional outcomes, psychological distress reduction, and improving HR-QOL.
Peripheral neuropathy in SS should be diagnosed and treated properly. Currently, there are no guidelines based on randomized trials regarding the treatment of patients with SS with nervous system involvement. Patients with oligosymptomatic and self-limiting course of the disease do not require pharmacological treatment. Immunosuppressive treatment is applied in case of high disease activity or progressive course of the nervous system involvement [28, 29]. In the symptomatic treatment of neuropathic pain, anti-epileptic drugs, antidepressants, and opioids are being used [28]. In the presence of pain, regardless of its nature and cause, effective treatment is necessary to improve patients’ QOL.
In summary, these preliminary results suggest a large unmet health burden. SS patients are a very diverse group of patients with possible involvement of every organ and system, and therefore, the rheumatologists’ broad knowledge and interdisciplinary approach to these patients are relevant. We should remember that patients value their QOL more than disease activity indexes or laboratory parameters. This is the first study that emphasizes the relationship between PNS involvement and worse HR-QOL in pSS patients. An attempt to expand the pain assessment with its categorization into muscular, articular, and neuropathic is also a novelty in this group of patients. The above conclusions indicate the direction of future research in this group of patients, focused on the rapid detection of organ-specific complications with subsequent appropriate treatment. In addition, they indicate the need to pay more attention to the subjective symptoms reported by patients and their careful assessment. Further research seems to be needed on the pathomechanism of pain formation and its perception in pSS. Also the development of new scales to accurately assess pain and other patient-reported complaints seems necessary. It should be emphasized that pain in rheumatological patients is a much more complex problem than it seemed. As an attending physician, rheumatologist should take care of every aspect of the patient’s life, starting from controlling disease activity, effective pain treatment, through improvement of daily functioning, and finally mental well-being.