Polyneuropathy

Procedure

With the patient's eyes closed, press a 10 g monofilament at right angles onto the skin until it bends, for about 1–2 seconds, at standard sites on each foot (great toe pad and metatarsal heads), avoiding callus. Ask the patient to say when they feel it.

Positive Finding

The monofilament is not felt at one or more sites.

Sensitivity / Specificity

Reference: Wang F, Zhang J, Yu J, Liu S, Zhang R, Ma X, et al. Diagnostic Accuracy of Monofilament Tests for Detecting Diabetic Peripheral Neuropathy: A Systematic Review and Meta-Analysis. J Diabetes Res. 2017;2017:8787261. Perkins BA, Olaleye D, Zinman B, Bril V. Simple screening tests for peripheral neuropathy in the diabetes clinic. Diabetes Care. 2001;24(2):250-6.

Interpretation

Identifies feet that have lost protective sensation and are at risk of ulcers, which need podiatry and foot-care advice. Weakness spreading up from the feet over days, especially with breathing or swallowing difficulty, suggests Guillain–Barré syndrome: emergency care. Neuropathy that is asymmetric, mainly motor or worsening quickly needs prompt neurology referral. Pooled from a 2017 meta-analysis of 8 studies in people with diabetes or impaired glucose tolerance, with nerve conduction studies as the reference (Wang et al.); studies using healthy controls were excluded. The monofilament misses about half of people with neuropathy, so a normal result does not rule it out; it is best at identifying feet that have lost protective sensation and are at risk of ulcers. In the largest single study (Perkins 2001, 478 people) an abnormal result made neuropathy much more likely (likelihood ratio 10.2).

Procedure

Strike a 128 Hz tuning fork and place it on the bony top of the great toe (end joint). Ask the patient to say when they feel the vibration and when it stops; damp it at random to check. Move up to the ankle and knee if absent.

Positive Finding

Vibration not felt, or felt to stop much earlier than at a comparison site.

Interpretation

Loss of vibration sense in the toes, spreading upwards, is typical of a length-dependent polyneuropathy. Vibration sense also declines with age. In 478 people attending a diabetes clinic, tested blind against nerve conduction studies (Perkins 2001), an abnormal on-off vibration result (5 or more wrong answers out of 8) made neuropathy much more likely (likelihood ratio 26.6), and a normal result (1 or no wrong answers) made it less likely (0.33). The abstract does not give sensitivity and specificity, so no figure is shown.

Procedure

Using a single-use neurological pin, test sharp sensation on the top of the great toe, then move up the leg to find where feeling returns to normal. Compare sides.

Positive Finding

Reduced sharp sensation in the feet, with a level up the leg where it becomes normal (a 'stocking' pattern).

Interpretation

A stocking pattern on both sides is typical of polyneuropathy; loss on one side or in one nerve's area suggests a single nerve or root problem instead. In 478 people attending a diabetes clinic, tested blind against nerve conduction studies (Perkins 2001), an abnormal superficial pain (pin-prick) result (5 or more wrong answers out of 8) made neuropathy much more likely (likelihood ratio 9.2), and a normal result (1 or no wrong answers) made it less likely (0.50). The abstract does not give sensitivity and specificity, so no figure is shown.

Procedure

The patient stands from a standard chair, walks 3 metres at their normal pace, turns, walks back and sits down. Time it, and stay close to prevent falls.

Positive Finding

A slow time or unsteady performance.

Reference: Podsiadlo & Richardson, 1991, Journal of the American Geriatrics Society; Franchignoni et al., 2013, BJSM

Interpretation

Measures mobility and falls risk and tracks change; it does not diagnose neuropathy.

Procedure

The patient stands with feet together, arms by the sides, eyes open, then eyes closed for up to 30 seconds. Stand close enough to catch them.

Positive Finding

Clearly more sway or a loss of balance with eyes closed compared with eyes open.

Interpretation

Suggests loss of position sense in the feet (sensory ataxia), as in large-fibre neuropathy. Unsteadiness with eyes open as well suggests a cerebellar or other cause. The figure previously stored had no traceable source, so no figure is shown.

Procedure

With the patient kneeling on a chair or lying with the foot supported, tap the Achilles tendon; use reinforcement (clenching the teeth or pulling the hands apart) if absent. Compare with the knee reflexes.

Positive Finding

Reduced or absent ankle reflexes on both sides with knee reflexes preserved.

Interpretation

Fits a length-dependent polyneuropathy. Ankle reflexes can be reduced in older people without neuropathy, and loss on one side suggests an S1 root problem. Common causes to check with the GP include diabetes, low vitamin B12, alcohol, thyroid disease and chemotherapy. The figure previously stored was attributed to studies that did not test the ankle reflex (Perkins 2001 tested four sensory tests only), so no figure is shown.