Thermal threshold testing: call for a balance between the number of measurements and abnormalities in the diagnosis of sarcoidosis-associated small fiber neuropathy

New phenotyping questionnaire for diagnosing sarcoidosis-associated small fiber neuropathy

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 are more often present with a non-length-dependent small fiber neuropathy. Detailed phenotyping may be useful to improve diagnostic efficiency, as a clue to underlying mechanisms and as a 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 musculoskeletal pain. The distinction between intermittent and continuous symptoms showed significantly less continuous than intermittent non-length-dependent symptoms (odds ratio = 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 the diagnostic methods used.

Inter-trial Variation in the Sensitivity of Thermal Threshold Testing for the Diagnosis of Neuropathy in Type 2 Diabetes Mellitus

BACKGROUND

Thermal threshold testing (TTT) is a simple non-invasive approach for diagnosing diabetic neuropathy earlier. Conventionally the TTT is done in all four limbs and at least 6 trials are done to obtain the mean threshold, which is time consuming.

AIM

We propose to assess the validity and reliability of reduced number of trials of TTT in the lower limbs.

MATERIALS AND METHODS

After obtaining ethics approval from the Institute Ethics Committee, 100 patients with type 2 Diabetes Mellitus of both gender between the ages of 35 to 65 years attending medicine OPD were recruited. Neuropathy assessment was done using Temperature threshold testing. At least 6 trials were performed for each site and the mean threshold obtained. The mean of 5 trials, 4 trials and 3 trials were noted for the comparison.

RESULTS

On comparing hot tests of 3 trials with 6 trials had a sensitivity and specificity of 88.7% and 96.6 %. In cold threshold testing, 4 trials and 3 trials showed similar results of sensitivity of 77.8%, specificity of 98.8%. The measures of agreement between the hot trials 6 vs 5 had Kappa value of 0.953, 6vs 4 showed a Kappa value of 0.862 and 6 vs 3 showed Kappa value of 0.819.

CONCLUSION

Hot threshold tests of lower limb are more sensitive than cold thresholds. The 4 trial test is a reliable test and can be performed over 6 trial tests. When time is a factor, three trials are sufficient to diagnose small fibre neuropathy.

Fully Automatic, Semiautomatic, and Manual Corneal Nerve Fiber Analysis in Patients With Sarcoidosis

Purpose

No guidelines are available on the preferred method for analyzing corneal confocal microscopy (CCM) data. Manual, semiautomatic, and automatic analyzes are all currently in use. The purpose of the present study was threefold. First, we aimed to investigate the different methods for CCM analysis in patients with and without small fiber neuropathy (SFN). Second, to determine the correlation of different methods for measuring corneal nerve fiber length (CNFL) and nerve fiber area (NFA). Finally, we investigated the added value of automatic NFA analysis.

Methods

We included 20 healthy controls and 80 patients with sarcoidosis, 31 with established SFN and 49 without SFN. The CNFL was measured using CCMetrics, ACCMetrics, and NeuronJ. NFA was measured with NFA FIJI and ACCMetrics NFA.

Results

CNFL and NFA could not distinguish sarcoidosis with and without SFN or healthy controls. CCMetrics, NeuronJ, and ACCMetrics CNFL highly correlated. Also, NFA FIJI and ACCMetrics NFA highly correlated. Reproducing a nonlinear formula between CNFL and NFA confirmed the quadratic relation between NFA FIJI and ACCMetrics CNFL. CCMetrics and NeuronJ instead showed a square root relationship and seem to be less comparable owing to differences between automatic and manual techniques.

Conclusions

ACCMetrics can be used for fully automatic analysis of CCM images to optimize efficiency. However, CNFL and NFA do not seem to have a discriminatory value for SFN in sarcoidosis. Further research is needed to determine the added value and normative values of NFA in CCM analysis.

Translational Relevance

Our study improves the knowledge about CCM software and pathophysiology of SFN.