Exploration of small fibers for testing diabetic neuropathies

Electrophysiological exploration of neuropathies is a standard method of investigating the dysfunction of myelinated larger fibers (Aalpha, Abeta). However, this method cannot test dysfunctions in other fibers. To evaluate the smaller (Adelta) and unmyelinated fiber (C-fibers) lesions a quantitative method has been perfected: the study of the sensory thresholds (quantitative sensory testing: QST). It allows the investigation of the sensory symptoms and is a reproducible, non-invasive and painless method. It is used above all in patients suffering from diabetic neuropathy ('Diabetes Care 9 (1987) 432').

We used the QST testing in comparison with nerve conduction velocities in 40 Non-Insulin-Dependent Diabetes Mellitus (NIDDM or Type II) patients in their 60s (+/-10 years). Depending on the duration of their diabetes (dd), we distinguished three groups: dd < 5 years (GI) dd from 5 to 15 years (GII) and dd > 15 years (GIII). All the patients underwent a clinical neurological examination, which enabled us to establish a gravity score comparable to the NDS (Neuropathy Disability Score: 'Muscle Nerve 10 (1988) 21').

Nerve conduction velocities and QST were studied for each group of patients. Electrophysiological alterations were connected to the gravity clinical score and in some asymptomatic patients a higher QST heat threshold could be observed.

These results indicate that QST can detect the early dysfunction of the unmyelinated fibers in this kind of neuropathy. Subclinical detection can reduce severe neurological complications and make possible an early and effective treatment.