Assessment of sudomotor dysfunction using Neuropad and Sudoscan in diabetic polyneuropathy

Aims:

The relative performance of sudomotor function tests in detecting diabetic sensorimotor polyneuropathy (DSPN) has not yet been compared. The benefit from quantitative Neuropad analysis needs to be evaluated.

Methods:

Sudomotor function was assessed at the sole of the foot of individuals with T1D (diabetes duration (DD) [n]: ≤1 year [n = 55], 5 years [n = 55], and T2D (≤1 year [n = 84], 5 years [n = 100], 10 years [n = 27]) and NGT [n = 78] and with painless (-p) and painful DSPN (+p) (n = 149/148, DD [mean ± SD]: 16.7 ± 13.1/16.6 ± 11.6 years) using Sudoscan (electrochemical skin conductance (ESC)) and Neuropad, quantified with Sudometrics software. Intraepidermal nerve fiber density (IENFD) was determined in 189 individuals. Sudomotor dysfunction was defined at values (Neuropad-Sudometrics/Sudoscan) below the age-dependent 5th percentile of controls.

Results:

The percentages of individuals with sudomotor dysfunction according to Neuropad-Sudometrics and Sudoscan were similar within the groups: controls: 3.8 vs. 3.8%, T1D≤1yr: 3.6 vs. 1.8%, T1D-5yr: 5.5 vs. 5.5%, T2D≤1yr: 10.7 vs. 4.8%, T2D-5yr: 12.0 vs. 10.0%, T2D-10yr: 18.5 vs. 18.5%, DSPN-p: 28.9 vs. 27.5%, and DSPN+p: 29.7 vs. 33.1%. ESC was lower in DSPN+p vs. -p (63 ± 20 vs. 58 ± 21µS; P = 0.016). Neuropad-Sudometrics correlated with ESC in DSPN (r = 0.422; p ≤0.001). Both tests were associated with IENFD (Neuropad-Sudometrics/ESC: β= 0.331/0.293; p ≤0.01). Sensitivity and specificity for Neuropad-Sudometrics vs. ESC were 37% vs. 41% and 87% vs. 90%.

Conclusions:

Sudoscan detected slightly greater sudomotor dysfunction than Neuropad-Sudometrics in painful vs. painless DSPN at overall similar diagnostic performance. Both tests were highly specific for the diagnosis of small-fiber neuropathy. Sudomotor function was largely preserved in recent-onset diabetes.