Thermal threshold: research study on small fiber dysfunction in distal diabetic polyneuropathy

Area of Science:

• Neurology
• Diabetology
• Clinical Neurophysiology

Background:

• Diabetic neuropathy (DN) diagnosis commonly relies on nerve conduction (NC) studies.
• Small fiber damage often precedes large fiber damage in DN.
• Early diagnosis of DN is crucial for effective management.

Purpose of the Study:

• To evaluate the efficacy of the thermal threshold (TT) test for early detection of small fiber damage in asymptomatic type 2 diabetes mellitus (T2DM) patients.
• To compare the diagnostic yield of TT testing versus NC testing for DN.
• To investigate the potential of TT testing to reduce false negatives in DN diagnosis.

Main Methods:

• Seventy asymptomatic T2DM patients with suboptimal glycemic control (HbA1c 7-8%) and no other neuropathy causes were included.
• Both thermal threshold (TT) testing and sensory/motor nerve conduction (NC) studies were performed on upper and lower limbs.
• Patients had diabetes duration of 1-48 months and were on oral hypoglycemic medication.

Main Results:

• Nerve conduction (NC) showed abnormalities in 19% of patients (large fiber neuropathy).
• Thermal threshold (TT) testing revealed abnormalities in 43% of patients (small fiber neuropathy).
• NC exhibited a 57% false-negative rate for DN, while TT identified a higher frequency of neuropathy, particularly small fiber involvement, at an earlier stage.

Conclusions:

• The TT test is more sensitive than NC for detecting neuropathy in asymptomatic T2DM patients.
• Studying small fiber function via TT testing before large fiber function via NC is recommended for diagnosing distal symmetrical DN.
• TT testing offers a valuable tool for earlier and more accurate diagnosis of diabetic neuropathy.