SUDOSCAN combined to other diagnosis tests to confirm small fiber neuropathy


V. Fabry, A. Gerdelat, B. Acket, P. Cintas, V. Rousseau, E. Uro-Coste, S. M. Evrard and A. Pavy-Le Traon.
Article title: “Which Method for Diagnosing Small Fiber Neuropathy?”
Front. Neurol., 05 May 2020.

In a recent study conducted at Toulouse University Hospital, France, Vincent FABRY et al outlined the benefits of combining different diagnosis methods of Small Fiber Neuropathy (SFN) including SUDOSCAN measurement.

The diagnostic value of 6 methods evaluating small sensory and autonomic nerve fibers was determined: skin biopsy, Quantitative Sensory Testing (QST), quantitative sweat measurement system (Q-Sweat), Laser Evoked Potentials (LEP), Electrochemical Skin Conductance (ESC) measurement of SUDOSCAN and Autonomic CardioVascular Tests (ACVT) to evaluate the most relevant diagnostic strategy.

This single center retrospective study was conducted on 245 patients tested for symptoms compatible with SFN between 2013 and 2016 (see Figure 1 for possible etiologies).

The specificity (Sp) and sensitivity (Se) of each test were calculated based on the final diagnosis and the best diagnostic strategy. The final diagnosis (“Definite SFN,” “Possible SFN” or “No SFN”) was combined to clinical data and anomalies in at least 2 of the 6 tests as diagnostic criteria for SFN.

Diagnosis performances of SUDOSCAN were Sp of 89 % and Se of 60 % and the only significant inter-test correlation was between skin biopsy and ESC.
It should be underlined that Autonomic Cardiovascular Tests (ACVT) were not relevant.

The best combination of tests to diagnose SFN comprises skin biopsy, LEP, ESC, and QST that generates a PPV (Positive Predictive Value) of 90%, specificity of 88%, sensitivity of 92% and a NPV (Positive Predictive Value) of 91% (see Table 1).

These results demonstrated the utility of SUDOSCAN combined with other diagnosis tests to confirm SFN within a suspected population with SFN symptoms.

Figure 1

Prevalence of possible cause in patients with definite Small Fiber Neuropathy for whom aetiological investigations were documented.

Table 1

Comparison of different diagnostic strategies for small fiber neuropathy.

QST, Quantitative Sensory Testing; ESC, Electrochemical Skin Conductance; LEP, Laser Evoked Potentials; PPV, Positive Predictive Value; NPV, Negative Predictive Value.

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