Long-term efficacy of immunoglobulins in small fiber neuropathy related to Sjögren’s syndrome

A role for pathogenic autoantibodies in small fiber neuropathy?

The immune system has a role in neuropathic pain which includes autoimmune mechanisms (e.g., autoantibodies). Clinical studies have identified a number of conditions where neuropathic pain is common and that are associated with autoantibodies targeting antigens within the nervous system. Interestingly sensory symptoms can be relieved with immunotherapies or plasma exchange, suggesting that pain in these patients is antibody-mediated. Recent preclinical studies have directly addressed this. For example, passive transfer of CASPR2 autoantibodies from patients cause increased pain sensitivity and enhanced sensory neuron excitability in mice confirming pathogenicity and demonstrating that patient autoantibodies are a mechanism to cause neuropathic pain. Small fiber neuropathy (SFN) exclusively affects small sensory fibers (typically nociceptors) and is characterized by severe neuropathic pain. Known causes include diabetes, B12 deficiency and rare variants in sodium channel genes, although around 50% of cases are idiopathic. SFN is associated with autoimmune conditions such as Sjorgen's syndrome, Sarcoidosis and Celiac disease and immunotherapy in the form of Intravenous immunoglobulin (IVIG) has proved an effective treatment. Autoantibodies have been identified and, in some cases, passive transfer of SFN patient IgG in mice can recapitulate neuropathic pain-like behavior. Here we will discuss clinical and preclinical data relating to the idea that pathogenic autoantibodies contribute to SNF. We discuss putative pathogenic antibodies, cellular targets and the molecular mechanisms by which they cause sensory neuron damage and the development of neuropathic pain. Finally, we will comment on future directions which may provide further insights into the mechanisms underlying SFN in patients.

Sjögren's syndrome with and without neurological involvement

OBJECTIVE

Neurological manifestations of Sjögren's syndrome can be severe but also treatment-responsive. We aimed to systematically evaluate neurological manifestations of primary Sjögren's syndrome and find clinical features allowing sufficient identification of affected patients (pSSN) among those with Sjögren's syndrome without neurological involvement (pSS).

METHODS

Para-/clinical features of patients with primary Sjögren's syndrome (2016 ACR/EULAR classification criteria) were compared between pSSN and pSS. At our university-based center, patients with suggestive neurological symptoms undergo screening for Sjögren's syndrome, and newly diagnosed pSS patients are thoroughly evaluated for neurologic involvement. pSSN disease activity was rated by the Neurological Involvement of Sjögren's Syndrome Disease Activity Score (NISSDAI).

RESULTS

512 patients treated for pSS/pSSN at our site between 04/2018 and 07/2022 were included (238 pSSN patients [46%] vs. 274 pSS patients [54%], cross-sectional design). Independent predictors of neurological involvement in Sjögren's syndrome were male sex [p < 0.001], older age at disease onset [p < 0.0001], hospitalization at first presentation [p < 0.001], lower IgG levels [p = 0.04] and higher eosinophil values (treatment-naïve) [p = 0.02]. Univariate regression additionally showed older age at diagnosis [p < 0.001], lower prevalence of rheumatoid factor [p = 0.001], SSA(Ro)/SSB(La) antibodies [p = 0.03; p < 0.001], higher white blood cell count [p = 0.02] and CK levels [p = 0.02] (treatment-naïve) in pSSN.

INTERPRETATION

Patients with pSSN had different clinical characteristics than patients with pSS and represented a large proportion of the cohort. Our data suggest that neurological involvement in Sjögren's syndrome has been underestimated. Intensified screening for neurologic involvement should be included in the diagnostic algorithm for Sjögren's syndrome, especially in males of older age and with severe disease course requiring hospitalization.

Clinical and paraclinical features of small fiber neuropathy in Sjögren's syndrome

Sjögren's syndrome is a potentially treatable cause of Small Fiber Neuropathy (SFN)-a condition that severely affects patients' quality of life. We therefore aimed to characterize patients with SFN and Sjögren's syndrome to raise awareness of this disease and facilitate its early recognition as an essential step for appropriate treatment. In 97 SFN patients (median age 48 years, 77% female), we studied the clinical features associated with Sjögren's syndrome compared to the idiopathic SFN subtype. According to the current ACR/EULAR classification criteria (Shiboski et al., Ann Rheum Dis 76:9-16, 2017), 24/97 individuals (25%, median age 48.5 years, 75% female) were diagnosed with Sjögren's syndrome. We did not observe any differences in SFN-defining sensory plus symptoms. Furthermore, intraepidermal nerve fiber densities (IENFD) were significantly lower in patients with SFN and Sjögren's syndrome (mean 2.6 ± 1.2/mm) compared to patients with idiopathic SFN (mean 3.2 ± 1.5/mm; p = 0.048). There were no significant group differences when analyzing cerebrospinal fluid (CSF) parameters. We conclude that Sjögren's syndrome-associated SFN is difficult to distinguish from idiopathic forms based on initial clinical symptoms and CSF results. However, lower IENFD values in patients with Sjögren's syndrome-associated SFN might indicate a distinct different pathomechanism in this entity compared to idiopathic SFN.

Comparison of cutaneous silent period parameters in patients with primary Sjögren's syndrome with the healthy population and determination of ıts relationship with clinical parameters

Small fiber neuropathy (SFN) is one of the main neurological manifestations in primary Sjögren's Syndrome (pSS). For the detection of SFN, cutaneous silent period (CSP) measurement is gaining popularity recently due to its non-invasiveness and practical application. Evaluating SFN involvement in patients with pSS using CSP and evaluating its relationship with clinical parameters. Patients with a diagnosis of pSS and healthy volunteers demographically homogeneous with the patient group were included in the study. The CSP responses were recorded over the abductor pollicis brevis muscle. The latency and duration values of the responses were obtained. In patient group, EULAR Sjögren's Syndrome Patient Reported Index (ESSPRI), Hospital Anxiety and Depression Scale (HADS), Short Form-36 (SF-36) questionnaire, Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) and Central Sensitization Inventory (CSI) were applied for the evaluation of symptom severity, mood, quality of life, presence of neuropathic pain and central sensitization, respectively. The mean CSP latency was significantly longer in patient group compared to control group (p < 0.001). Mean CSP duration was also significantly shorter in patient group (p < 0.001). There were no significant differences in CSP parameters according to patients' neuropathic pain or central sensitization profile. There were significant correlations of CSP parameters (latency and duration, respectively) with ESSPRI dryness (ρ = 0.469, p = 0.004; ρ =  -0.553, p < 0.001), fatigue (ρ = 0.42, p = 0.011; ρ =  -0.505, p = 0.002), pain (ρ = 0.428, p = 0.009; ρ =  -0.57, p < 0.001) subscores and mean ESSPRI score (ρ = 0.631, p < 0.001; ρ = -0.749, p < 0.001). When SF-36 subscores and CSP parameters were investigated, a significant correlation was found only between "bodily pain" subscore and CSP duration (ρ =  -0.395, p = 0.017). In HADS, LANSS and CSI evaluations, a significant correlation was found only between HADS anxiety score and the CSP duration (ρ = 0.364, p = 0.02). As indicated by CSP measurement, SFN is more prominent in patients with pSS than in the healthy population. It is important to investigate the presence of SFN because of its correlation with the leading symptoms in the clinical spectrum of pSS.

Analysis of clinical features and risk factors of peripheral neuropathy in patients with primary Sjögren's syndrome

OBJECTIVE

To observe the clinical features and efficacy of immunosuppressive therapy in patients with primary Sjögren's syndrome (PSS) combined with peripheral neuropathy (PN) syndrome and to explore the risk factors for PN in patients with PSS.

METHODS

Sixty consecutive patients with PSS admitted to the Department of Rheumatology and Immunology, Wuhan No. 1 Hospital, from January 2014 to June 2020 were analysed retrospectively. Patients were divided into a PN group (N = 15) and a non-PN group (N = 45). The clinical characteristics of the two groups were compared, and the independent risk factors for PN combined with PSS were analysed by multivariate logistic regression. The patients with PSS combined with PN were followed up to observe the effect of immunosuppressive therapy.

RESULTS

The patients with PN had a longer course of disease than those without PN (z = - 3.225, P = 0.001), and the incidence of Raynaud's phenomenon, anti-SSB antibody, rheumatoid factor and hyperglobulinaemia was higher (all P < 0.05) in patients with PN than in those without PN. Multivariate logistic regression analysis showed that hyperglobulinaemia, RF and anti-SSB antibodies were independent risk factors for PN with PSS (P < 0.05). Fourteen patients with PSS-PN were treated with immunosuppressants. The clinical symptoms of 10 patients were relieved, and mRS scores of 10 patients were decreased.

CONCLUSION

PN is a common complication in PSS patients. Patients with PSS combined with PN have a longer course of disease and a significantly higher percentage of Raynaud's phenomenon, positive anti-SSB antibody, positive RF and hyperglobulinaemia. Immunosuppressive therapy was effective for partial remission of PN with PSS.

Primary Sjögren syndrome-related peripheral neuropathy: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

Primary Sjögren syndrome (pSS) is a chronic, systemic, autoimmune disorder characterized by lymphocytic infiltrates of the exocrine organs, leading to sicca symptoms and parotid enlargement. pSS has been linked to various neurological manifestations, including peripheral neuropathy (PN). We aimed to provide a comprehensive analysis of the currently available evidence regarding pSS-related PN.

METHODS

A literature search in the PubMed database was performed, and 49 papers were eligible to be included in this systematic review and meta-analysis.

RESULTS

The pooled prevalence of PN in pSS is estimated to be 15.0% (95% confidence interval = 10.7%-20.7%). The mean age of pSS patients at PN diagnosis is 59 years. Among the patients with pSS and PN, 83% are females. Neuropathic symptoms usually precede or lead to the pSS diagnosis at a 2:1 ratio in patients with pSS-related PN. The commonest type of pSS-related PN is distal axonal polyneuropathy (80% of patients with pSS-related PN), followed by sensory ganglionopathy. Peripheral and cranial mononeuropathies-particularly trigeminal-are also frequent. Risk factors for developing PN include increasing age and presence of vasculitis. Immune-mediated pathogenetic mechanisms are discussed. Glucocorticoids are the most commonly used treatment option for managing pSS-related PN, when associated with vasculitis, followed by the use of intravenous immunoglobulin.

CONCLUSIONS

PN is very common in pSS patients. Evidence on long-term prognosis of PN in pSS is limited, and further research is needed. Research into the use of immunosuppressive medication in nonvasculitic neuropathies in the context of pSS merits further consideration.

Small fiber neuropathies: expanding their etiologies

PURPOSE OF REVIEW

Several conditions have been associated with the development of small fiber neuropathy (SFN). The list of metabolic, immune-mediated, infectious, toxic, drugs-related, and hereditary conditions is still growing and various hypotheses are made about the underlying pathophysiological mechanisms. Understanding these processes is important to provide new targets for treatment. In addition, the specific SFN phenotype can provide direction for the underlying etiology. This review discusses the latest developments concerning the expanding etiologies in SFN.

RECENT FINDINGS

In the past 18 months, special attention has been paid to immunological etiologies, partly due to the coronavirus disease 2019 pandemic, but also new auto-antibodies in SFN have been demonstrated. Identifying patients with immune-mediated SFN can be challenging, since contrary to the classical distal sensory phenotype, a nonlength-dependent pattern is more common.Besides the etiologies of classical SFN, small fiber pathology is increasingly described in diseases without the typical neuropathic pain features of SFN, sometimes called syndromic SFN. However, the clinical relevance is not yet fully understood.

SUMMARY

The expansion of the etiologies of SFN continues and brings more insight in possible targets for treatment. The clinical presentation may vary as a result of the underlying condition.

Small fiber neuropathy

Small fiber neuropathy (SFN) is a peripheral nervous system disease due to affection of A-delta or C-fibers in a proximal, distal, or diffuse distribution. Selective SFN (without large fiber affection) manifests with pain, sensory disturbances, or autonomic dysfunction. Though uniform diagnostic criteria are unavailable, most of them request typical clinical features and reduced intra-epidermal nerve fiber density on proximal or distal skin biopsy. Little consensus has been reached about the treatment of SFN, why this narrative review aims at summarizing and discussing treatment options for SFN. Treatment of SFN can be classified as symptomatic, pathophysiologic, or causal. Prerequisites for treating SFN are an established diagnosis, knowledge about the symptoms and signs, and the etiology. Pain usually responds to oral/intravenous pain killers, antidepressants, anti-seizure drugs, or topical, transdermal specifications. Some of the autonomic disturbances respond favorably to symptomatic treatment. SFN related to Fabry disease or hATTR are accessible to pathogenesis-related therapy. Immune-mediated SFN responds to immunosuppression or immune-modulation. Several of the secondary SFNs respond to causal treatment of the underlying disorder. In conclusion, treatment of SFN relies on a multimodal concept and includes causative, pathophysiologic, and symptomatic measures. It strongly depends on the clinical presentation, diagnosis, and etiology, why it is crucial before initiation of treatment to fix the diagnosis and etiology. Due to the heterogeneous clinical presentation and multi-causality, treatment of SFN should be individualized with the goal of controlling the underlying cause, alleviating pain, and optimizing functionality.

Novel Autoantibodies in Idiopathic Small Fiber Neuropathy

Objective

Small fiber neuropathy (SFN) is clinically and etiologically heterogeneous. Although autoimmunity has been postulated to be pathophysiologically important in SFN, few autoantibodies have been described. We aimed to identify autoantibodies associated with idiopathic SFN (iSFN) by a novel high‐throughput protein microarray platform that captures autoantibodies expressed in the native conformational state.

Methods

Sera from 58 SFN patients and 20 age‐ and gender‐matched healthy controls (HCs) were screened against >1,600 immune‐related antigens. Fluorescent unit readout and postassay imaging were performed, followed by composite data normalization and protein fold change (pFC) analysis. Analysis of an independent validation cohort of 33 SFN patients against the same 20 HCs was conducted to identify reproducible proteins in both cohorts.

Results

Nine autoantibodies were screened with statistical significance and pFC criteria in both cohorts, with at least 50% change in serum levels. Three proteins showed consistently high fold changes in main and validation cohorts: MX1 (FC = 2.99 and 3.07, respectively, p = 0.003, q = 0.076), DBNL (FC = 2.11 and 2.16, respectively, p = 0.009, q < 0.003), and KRT8 (FC = 1.65 and 1.70, respectively, p = 0.043, q < 0.003). Further subgroup analysis into iSFN and SFN by secondary causes (secondary SFN) in the main cohort showed that MX1 is higher in iSFN compared to secondary SFN (FC = 1.61 vs 0.106, p = 0.009).

Interpretation

Novel autoantibodies MX1, DBNL, and KRT8 are found in iSFN. MX1 may allow diagnostic subtyping of iSFN patients. ANN NEUROL 2022;91:66–77

Non-length-dependent small fiber neuropathy: Not a matter of stockings and gloves

The clinical spectrum of small fiber neuropathy (SFN) encompasses manifestations related to the involvement of thinly myelinated A-delta and unmyelinated C fibers, including not only the classical distal phenotype, but also a non-length-dependent (NLD) presentation that can be patchy, asymmetrical, upper limb-predominant, or diffuse. This narrative review is focused on NLD-SFN. The diagnosis of NLD-SFN can be problematic, due to its varied and often atypical presentation, and diagnostic criteria developed for distal SFN are not suitable for NLD-SFN. The topographic pattern of NLD-SFN is likely related to ganglionopathy restricted to the small neurons of dorsal root ganglia. It is often associated with systemic diseases, but about half the time is idiopathic. In comparison with distal SFN, immune-mediated diseases are more common than dysmetabolic conditions. Treatment is usually based on the management of neuropathic pain. Disease-modifying therapy, including immunotherapy, may be effective in patients with identified causes. Future research on NLD-SFN is expected to further clarify the interconnected aspects of phenotypic characterization, diagnostic criteria, and pathophysiology.