Noninvasive Sudoscan May Help Assess Severity of FAP in Patients, Study Suggests

A parameter called electrochemical skin conductance is linked to disease severity in patients with familial amyloid polyneuropathy (FAP), potentially supporting the use of a device called Sudoscan to assess the clinical evolution of the disease, according to researchers.

Their study, “The value of electrochemical skin conductance measurement using Sudoscan in the assessment of patients with familial amyloid polyneuropathy,” was published in the journal Clinical Neurophysiology.

FAP is a rare, inherited, and progressive disease characterized by nerve lesions due to the accumulation of amyloid fibers. The disease is caused by mutations in the TTR gene.

Recently, a new device called Sudoscan, developed by Paris-based Impeto Medical, was introduced into clinical practice to evaluate damages to peripheral nerves in patients with diabetes.

Sudoscan applies a small electrical stimulus to the skin of the hands and palms, leading to the production of a current, the electrochemical skin conductance (ESC). Decreases in ESC reflect loss or damages to small nerve fibers.

Now, researchers in France used Sudoscan to measure ESC in the hands and feet of 126 FAP patients with the Val30Met mutation (65 patients), the most common of more than 100 point mutations identified worldwide, and without the Val30Met (61) TTR mutation.

The 52 women and 74 men were ages 25 to 81 and ranged from asymptomatic FAP to mild and advanced stages of the disease.

The ESC measurements did not differ between the two subgroups of patients with Val30Met or non-Val30Met mutation.

Lower ESC measures were found in 24% of clinically asymptomatic patients, increasing to 65% of patients with moderate TTR-FAP, and 92% of patients with advanced TTR-FAP.

Accordingly, the results showed a good correlation between the ESC values and the clinical parameters used to assess the severity of the disease. These included the neuropathy impairment score, the modified Polyneuropathy Disability Score, the Karnofsky Performance Status, and body mass index (BMI), a measure of body fat.

The neuropathy impairment score is a comprehensive measure assessing motor and sensory function, as well as tendon reflexes. The Karnofsky Performance Status reflects the global health of the patient, and the polyneuropathy disability score evaluates patients’ walking abilities.

Overall, these results suggest that measuring ESC via Sudoscan can be used to assess the severity of TTR-FAP.

Also, “the clinical importance of measuring ESC could be to first to provide an early marker of the onset of the disease and then a biomarker of its evolution (including in patients with advanced neuropathy),” researchers wrote.

“Thus, Sudoscan could be useful for treatment decisions, whatever the type of TTR variant, even in non-Val30Met- patients,” they concluded.