The 2009 paper “Sweat testing to evaluate autonomic function” (Illigens & Gibbons, 2009) offers a deep dive into assessing sudomotor (sweat gland–related) function as a sensitive indicator of autonomic nerve health, especially in early diabetic neuropathy.
In patients with diabetes, small-diameter, unmyelinated nerve fibres—those that regulate sweating—are often among the first affected in peripheral neuropathy. Sudomotor dysfunction, characterised by abnormal sweating patterns, frequently surfaces even before large-nerve issues become clinically apparent.
The authors explain several testing methods, including thermoregulatory sweat testing, quantitative sudomotor axon reflex testing (QSART), sympathetic skin response, and alternative approaches like QDIRT. These techniques, particularly QSART and QDIRT, can precisely evaluate postganglionic sweat nerve fibre activity. The tests are non-invasive, reproducible when carefully controlled for confounders like room temperature and hydration, and critically useful for both early diagnosis and tracking disease progression or recovery.
Benefits of Sudomotor Testing in Diabetic Patients
From the evidence reviewed, the key advantages of testing for sudomotor dysfunction in diabetes emerge:
- Early Detection of Small-Fibre Neuropathy
Sudomotor abnormalities appear before symptoms like numbness or pain, making these tests a potent early warning tool for asymptomatic neuropathy. - Objective and Quantifiable Measurements
Tests such as QSART and QDIRT objectively measure sweat response to stimuli, offering precise, quantitative data that can guide both diagnosis and management over time. - Localization of Nerve Damage
These tests can help distinguish between preganglionic and postganglionic dysfunction and can map the distribution of nerve damage—vital for targeted interventions. - Monitoring Disease Progression and Treatment Response
Regular sudomotor testing allows clinicians to assess whether nerve function is worsening, stabilizing, or improving in response to treatment—ideally before irreversible damage occurs. - Versatility and Accessibility
Though some techniques (like QDIRT) need specialized labs, others are relatively simple, fast, and increasingly available in clinical settings, making them feasible for routine screening. - Complementary to Other Autonomic Measures
Sudomotor testing adds a crucial dimension to autonomic assessment, alongside cardiovascular evaluations like heart rate variability and tilt-table testing.
For diabetic patients, these benefits translate into tangible clinical value. Early identification of sudomotor dysfunction enables timely interventions—improving glycemic control, optimising lifestyle, or initiating therapies—to potentially halt or slow neuropathy progression before symptoms or complications like foot ulcers emerge. Moreover, because autonomic nerve impairment in diabetes is associated with increased cardiovascular risk, detecting sudomotor changes could guide clinicians to investigate and address broader systemic risks.
In summary, the reviewed paper positions sudomotor testing as a frontline tool in the early, objective, and nuanced evaluation of diabetic neuropathy. By identifying subtle nerve dysfunctions before they become debilitating, clinicians can act proactively—potentially improving outcomes and preserving quality of life for patients with diabetes.