Length-dependent Small Fiber Neuropathy Research Articles

New phenotyping questionnaire for diagnosing sarcoidosis-associated small fiber neuropathy

Abstract Small fiber neuropathy is a common complication in patients with sarcoidosis and its prevalence is estimated at 40-86%. The underlying mechanism influences the presentation of small fiber neuropathy. For example, patients with metabolic diseases are often associated with a classic length-dependent small fiber neuropathy pattern, while patients with inflammatory diseases more often present with a non-length-dependent small fiber neuropathy. Detailed phenotyping may be useful to improve diagnostic efficiency, as clue to underlying mechanisms and as precondition for personalized medicine. This study examined four phenotypes distinguishing between length-dependent and non-length-dependent presentation with a new subdivision for continuous and intermittent presentation. Forty-eight sarcoid patients with symptoms and at least two clinical signs of small fiber neuropathy and normal nerve conduction studies were classified as having probable small fiber neuropathy. A new small fiber neuropathy phenotyping questionnaire has been developed that allows patients to mark the anatomical locations of pain at three different levels: the skin, muscles and joints. The location of symptoms was used to define length dependence and two colors were used to distinguish continuous (red) from intermittent (blue) symptoms. In addition, skin biopsy, corneal confocal microscopy, Sudoscan and water immersion skin wrinkling were used to investigate a correlation between the four phenotypes, sensory function, nerve fiber density and autonomic nerve function. Overall, 35% of patients with probable small fiber neuropathy showed length-dependent symptoms and 44% showed non-length-dependent symptoms while 21% suffered from non-neuropathic muscoskeletal pain. The distinction between intermittent and continuous symptoms, showed significantly less continuous than intermittent non-length-dependent symptoms (OR=0.3, p=0.01). Moreover, continuous length-dependent symptoms were the only phenotype that correlated with thermal threshold testing (R=0.3; p=0.02) and the small fiber neuropathy screening list (R=0.3; p=0.03). In addition, thermal threshold testing (TTT) also correlated with the small fiber neuropathy (SFN) screening list (R=0.3; p=0.03). Other diagnostic methods showed no correlation with any of the four defined phenotypes. A novel finding is that TTT is only associated with continuous length-dependent pain, suggesting that TTT could result in more false negatives in patients with other pain phenotypes. Determining the pathophysiologic mechanisms could help develop new diagnostic methods. If patients suspected of SFN show symptoms without a length-dependent continuous presentation, the diagnosis should focus less on diagnostic methods used.

Initial validation of the Mass. General Neuropathy Exam Tool (MAGNET) for evaluation of distal small-fiber neuropathy.

Diagnosis of small-fiber neuropathy (SFN) is hampered by its subjective symptoms and signs. Confirmatory testing is insufficiently available and expensive, so predictive examinations have value. However, few support the 2020 SFN consensus-case-definition requirements or were validated for non-diabetes neuropathies. Thus we developed the Massachusetts General Hospital Neuropathy Exam Tool (MAGNET) and measured diagnostic performance in 160 symptomatic patients evaluated for length-dependent SFN from any cause and 37 healthy volunteers. We compared prevalences of abnormalities (vital signs, pupil responses, lower-limb appearance, pin, light touch, vibration and position sensitivity, great-toe strength, muscle stretch reflexes), and validated diagnostic performance against objective SFN tests: lower-leg skin-biopsy epidermal neurite densities and autonomic function testing (AFT). Sensitivity/specificity, feasibility, test-retest and inter-rater reliability, and convergence with the Utah Early Neuropathy Scale were calculated. Patients' ages averaged 48.5 ± 14.7 years and 70.6% were female. Causes of neuropathy varied, remaining unknown in 59.5%. Among the 46 with abnormal skin biopsies, the most prevalent abnormality was reduced pin sharpness at the toes (71.7%). Inter-rater reliability, test-retest reliability, and convergent validity excelled (range = 91.3-95.6%). Receiver operating characteristics comparing all symptomatic patients versus healthy controls indicated that a MAGNET threshold score of 14 maximized predictive accuracy for skin biopsies (0.74) and a 30 cut-off maximized accuracy for predicting AFT (0.60). Analyzing patients with any abnormal neuropathy-test results identified areas-under-the-curves of 0.87-0.89 for predicting a diagnostic result, accuracy = 0.80-0.89, and Youden's index = 0.62. Overall, MAGNET was 80%-85% accurate for stratifying patients with abnormal versus normal neuropathy test results. MAGNET quickly generates research-quality metrics during clinical examinations.

TS-HDS autoantibody: clinical characterization and utility from real-world tertiary care center experience.

To evaluate clinical utility of trisulfated-heparin disaccharide (TS-HDS) IgM testing from real-world tertiary care center experience. Medical records of patients with positive TS-HDS antibodies who were evaluated at Mayo Clinic from 2009 to 2022 were reviewed. Seventy-seven patients (50 females) had positive TS-HDS antibody. Median age was 48 (9-77) years. Median titer was 25,000 (range 11,000-350,000). Twenty-six patients (34%) did not have objective evidence of peripheral neuropathy. Nine patients (12%) had other known causes of neuropathy. Among the remaining 42 patients, half presented with subacute progressive course; the other half had chronic indolent course. Most common phenotypes were length-dependent peripheral neuropathy (n = 20, 48%), length-dependent small-fiber neuropathy (n = 11, 26%), and non-length-dependent small-fiber neuropathy (n = 7, 17%). Nerve biopsies showed epineurial inflammatory cell collections in 2 but no interstitial abnormalities in the remaining 7. The majority of intraepidermal nerve fiber densities (7/10), thermoregulatory sweat tests (12/21) and autonomic reflex screens (27/49) were normal. Post-immunotherapy improvement in mRS/INCAT disability score/pain was only seen in 13/42 (31%) TS-HDS IgM positive patients. Patients presenting with sensory ganglionopathy, non-length dependent small-fiber neuropathy, or subacute progressive neuropathy with and without TS-HDS antibody responded similarly to immunotherapy (40% vs 80%, p = 0.30). TS-HDS IgM has limited phenotypic or disease specificity; it was found to be positive among patients with various neuropathy phenotypes as well as patients without objective evidence of neuropathy. Clinical improvement with immunotherapy, although was observed in a small proportion of TS-HDS IgM seropositive patients, was not more frequent when compared to seronegative patients with similar presentations.

Longitudinal follow-up of biopsy-proven small fiber neuropathy.

Little is published on the prognosis of small fiber neuropathy (SFN). A retrospective analysis of 101 patients with biopsy proven SFN. Study participants included 87 patients with length-dependent SFN and 14 patients with non-length-dependent SFN. The average duration of symptoms was 3.2 years prior to SFN diagnosis, and the average follow-up duration after diagnosis was 6.2 years. Neuropathic pain was present in 98% of patients and in 84.2% of patients at the final visit. The average total number of pain medications ever used was 4.4 per patient. Signs of autonomic dysfunction were initially present in 24.8% of patients, but improved in most. Large fiber involvement was seen in 11.9% of patients. Small fiber neuropathy affected employment and ambulation status in 5.3% and 6.3% of patients, respectively. Small fiber neuropathy tends to be stable and rarely affects ambulation and employment status. Effective pain control remains a challenge.

Small fiber neuropathy in coeliac disease and gluten sensitivity

ABSTRACTObjectives: The commonest types of peripheral neuropathy in the context of Coeliac Disease (CD) and gluten sensitivity (GS) are length-dependent symmetrical sensorimotor neuropathies and sensory ganglionopathies. In patients with such neuropathy, (gluten neuropathy), peripheral neuropathic pain is prevalent suggesting involvement of small fibers. The purpose of this report was to describe the clinical characteristics of patients with CD or GS and pure small fiber neuropathy (SFN).Methods: We reviewed the records of all patients that had been referred to the Gluten-Related Neurological Disorders clinic who had clinical and neurophysiological evidence of SFN. All patients had serological evidence of gluten sensitivity (GS) prior to commencing GFD. All patients were offered a duodenum biopsy. Patients with comorbidities that could cause SFN were excluded.Results: We identified 13 patients (9 males) with SFN and gluten sensitivity. Of 11 patients who underwent duodenal biopsy 10 had evidence of enteropathy (CD). Mean age at onset of pain was 53.5 ± 11.4 years (range 34–72) and mean age of CD/GS diagnosis was 50.8 ± 10.4 years (range 34–68). In 8 patients (61.5%) pain was the presenting feature.Neurophysiological assessment suggested a length-dependent small fiber neuropathy in 11 patients, whereas in 2, a non-length dependent pattern was identifying suggesting that the predominant pathology lies in the dorsal root ganglia.Conclusion: SFN can be a presenting feature of CD and GS and, therefore, screening for CD and GS should be included in the diagnostic workup of patients with idiopathic SFN.

Familial Amyloid Polyneuropathy.

Transthyretin-related familial amyloid polyneuropathy (TTR-FAP) is a life-threatening disease caused by the accumulation of amyloidogenic transthyretin (TTR) protein in tissues. Mutations in TTR gene destabilize TTR protein to misfold from its native tetramer form to amyloidogenic monomer form. In endemic countries, TTR-FAP presents with length-dependent small fiber neuropathy, however in non-endemic countries clinical features can be highly variable. Genetic testing for TTR gene is mandatory for the diagnosis. Demonstrating amyloid deposits in tissues may be necessary for distinguishing symptomatic patients from asymptomatic carriers. Routine follow-up should include a wide range of tests to demonstrate systemic involvement. In recent years, treatment of TTR-FAP has significantly improved with new therapeutic approaches. TTR stabilizers and TTR-gene silencing drugs prevent the progression of the disease. Monoclonal antibodies that target amyloid deposits are currently under development. Early initiation of the treatment is important for better functional outcome.

'Sirim' (Cold) Pain as a Common Symptom in Korean Patients with Clinically Suspected Small-Fiber Neuropathy.

Background and PurposeDiagnosing small-fiber neuropathy (SFN) is challenging because there is no gold-standard test and few diagnostic tests. This study investigated the clinical symptom profile and its associations with the results of quantitative sensory testing (QST) and the quantitative sudomotor axon reflex test (QSART) as well as the quality of life (QOL) in patients with clinically suspected SFN.MethodsThis study involved 63 patients with clinically suspected length-dependent SFN. Assessments were performed using QST, QSART, SFN Symptoms Inventory Questionnaire, Neuropathic Pain Symptom Inventory, ‘Sirim’ frequency and ‘Sirim’ (cold) pain severity, and 36-item Short-Form Health Survey. Multiple logistic and linear regression analyses were performed to predict risk factors for QST or QSART abnormalities and QOL, respectively.Results‘Sirim’ and ‘Sirim’ pain was the most-common (84%) and the most-severe complaint (mean score of 6.3 on a numerical rating scale ranging from 0 to 10) in patients with clinically suspected SFN. The findings of QST [cold detection threshold (CDT)] and QSART were abnormal in 71% (n=45/57) and 62% (n=39/56) of the patients, respectively. An abnormal CDT was correlated with more-severe stabbing pain (odds ratio=2.23, 95% CI=1.02–4.87, p=0.045). Restless-leg symptoms (β=−7.077) and pressure-evoked pain (β=−5.034) were independent predictors of the physical aspects of QOL.Conclusions‘Sirim’ pain, similar to cold pain, should be considered a major neuropathic pain in SFN. Among pain characteristics, stabbing pain of a spontaneous paroxysmal nature may be more pronounced in the setting of dysfunctional Aδ fibers with functional autonomic C fibers.

The role of skin biopsy in differentiating small-fiber neuropathy from ganglionopathy.

We aimed to test the clinical utility of the leg:thigh intraepidermal nerve-fiber (IENF) density ratio as a parameter to discriminate between length-dependent small-fiber neuropathy (SFN) and small-fiber sensory ganglionopathy (SFSG) in subjects with signs and symptoms of small-fiber pathology. We retrospectively evaluated thigh and leg IENF density in 314 subjects with small-fiber pathology (173 with distal symmetrical length-dependent SFN and 141 with non-length-dependent SFSG). A group of 288 healthy subjects was included as a control group. The leg:thigh IENF density ratio was calculated for all subjects. We used receiver operating characteristic curve analyses to assess the ability of this parameter to discriminate between length-dependent SFN and SFSG, and the decision curve analysis to estimate its net clinical benefit. In patients with neuropathy, the mean IENF density was 14.8 ± 6.8/mm at the thigh (14.0 ± 6.9/mm in length-dependent SFN and 15.9 ± 6.7/mm in patients with SFSG) and 7.5 ± 4.5/mm at the distal leg (5.4 ± 3.2/mm in patients with length-dependent SFN and 10.1 ± 4.6/mm in patients with SFSG). The leg:thigh IENF density ratio was significantly (P < 0.01) lower in patients with length-dependent SFN (0.44 ± 0.23) compared with patients with SFSG (0.68 ± 0.28). The area under the curve of the receiver operating characteristic analysis to discriminate between patients with length-dependent SFN and SFSG was 0.79. The decision curve analysis demonstrated the clinical utility of this parameter. The leg:thigh IENF ratio represents a valuable tool in the differential diagnosis between SFSG and length-dependent SFN.

45. Skin nerve α-synuclein deposits as possible new biomarker for Dementia with Lewy bodies

The object of this study is to investigate whether: (1) phosphorylated α -synuclein (p-syn) deposits in peripheral nerves might represent a useful biomarker in dementia Lewy Body (DLB) helping to differentiate DLB from other forms of dementia; (2) small fiber neuropathy (SFN) may be part of DLB pathological picture contributing to autonomic dysfunctions. 20 well-characterized DLB patients (11 of them complaining autonomic symptoms particularly orthostatic hypotension) were studied together with 23 patients with dementia of different pathogenesis (Dementia without synuclein- DWS) including 13 patients fulfilling diagnostic criteria for Alzheimer’s disease, 6 with Frontotemporal Dementia and 4 with vascular dementia. Twenty-five age-matched healthy subjects served as controls. Subjects underwent: nerve conduction velocities from the leg to evaluate large nerve fibers; skin biopsy from proximal (i.e. cervical) and distal (i.e. thigh and distal leg) sites to study small nerve fibers and deposits of phosphorylated α -synuclein, considered the pathological form of α -synuclein. P-syn was not found in any skin sample in DWS patients and controls but it was found in all DLB patients with a proximal-distal gradient with all patients positive in the cervical site. Patients complaining of autonomic symptoms showed higher widespread positivity of analyzed skin samples than patients without autonomic symptoms. Furthermore DLB patients showed a length-dependent SFN particularly important in patients complaining autonomic symptoms. Conclusions: (1) p-syn in peripheral nerves is a sensitive biomarker for DLB diagnosis helping to differentiate DLB from other forms of dementia; (2) SFN was part of DLB pathological picture contributing to induce autonomic symptoms.

Is the Cornea a Window to Non–Length-Dependent Small-Fiber Neuropathy?

Confirming a diagnosis of small-fiber neuropathy usually requires specialized electrodiagnostic testing or histopathologic evaluation of intraepidermal

Elevated proinflammatory cytokine expression in affected skin in small fiber neuropathy

Small fiber neuropathy (SFN) is a subtype of sensory neuropathy with acral pain and normal findings in routine nerve conduction studies. Twenty-four patients with SFN and matched controls were prospectively studied in this case-control study. Patients were assessed clinically, with standardized pain and depression questionnaires, by neurophysiologic tests, and by quantitative sensory testing. All patients underwent skin punch biopsy in a clinically affected (distal calf) and a nonaffected area (proximal thigh). Blood samples were collected for systemic cytokine gene expression analysis. Patients with SFN had a 2-fold higher gene expression for interleukin (IL)-2 (p < 0.0001), IL-10 (p = 0.01), and transforming growth factor-beta1 (p = 0.001) in peripheral blood. Skin samples from affected areas showed increased IL-6 (7-fold; p = 0.001) and IL-8 (5-fold; p = 0.002) gene expression when compared to healthy controls. In 10/24 patients, SFN was termed length-dependent (LD) because of a > or =5-fold higher intraepidermal nerve fiber density in the proximal than in the distal skin. Patients with LD-SFN had higher gene expression in the affected distal skin than in nonaffected skin for tumor necrosis factor-alpha (2.6-fold; p = 0.04), IL-1beta (2-fold; p = 0.02), IL-6 (>200-fold; p = 0.01), and IL-8 (>500-fold; p = 0.046). Inflammatory cells were present in most SFN samples but their numbers were not correlated with cytokine levels. Elevated local proinflammatory cytokines may be involved in the pathophysiology of pain in length-dependent small fiber neuropathy. These findings suggest a potential therapeutic role of locally applied cytokine inhibitors.

Non‐length dependent small fiber neuropathy. A prospective case series

We report the features of non-length dependent small fiber neuropathy (SFN) and compare them to those with distal length-dependent SFN. In a series of 224 consecutive neuropathy patients, we evaluated 44 patients with SFN diagnosed in the presence of both symptoms and signs. Eleven were classified as non-length dependent SFN. Disease associations were Sjögren's syndrome (two patients), impaired glucose tolerance, rheumatoid arthritis, hepatitis C virus, Crohn's disease, and idiopathic (five patients). In the 33 patients with distal SFN, the age of onset was significantly older and more had impaired glucose metabolism (16/33). In both groups, pain was mainly characterized as burning, but patients with non-length dependent SFN more often reported an "itchy" quality and allodynia to light touch.

Rapid bedside heat-pain ratings are highly correlated with computer-aided QST: a direct comparison of fixed-stimulus intensity rating and CASE IV testing in patients with possible small fiber neuropathy

Routine clinical use of thermal QST using computer-aided devices is limited because the equipment is expensive and the protocols are time-consuming. Fixed-stimulus intensity rating is fast and can be performed in the context of a bedside examination with relatively inexpensive equipment. We compared heat-pain perception on the foot dorsum, using both techniques, followed by skin biopsy at the same site for epidermal nerve fiber (ENF) density evaluation, in 31 subjects with a clinical diagnosis of possible length-dependent small fiber neuropathy.