This article was publised in  No 3 of The Rondel (March 27, 2000)

Polyneuropathia in primary health care
Prof Jan Ekstedt, Bangårdsgatan 16, SE-753 20 Uppsala, Sweden
Jan@ekstedt.com

Polyneuropathia is distinguished by lesions in many, maybe all, nerves of the body. The etiology of the lesions may be an infection (e.g.acute anterior poliomyelitis), an immunological reaction towards a virus infection (e.g. the disease of Guillain-Barré), a toxic influence (alcohol, lead), a genetic disorder (familial amyloidosis with polyneuropathia), or metabolic disorders (diabetes mellitus, vitamin B12 deficiency).

The lesion may be diffuse all along the neuron – axonal neuropathy. On the other hand, the lesions may be multple and focal along the neuron.

The advanced polyneuropathia is characterized by .

• Disturbed skin sensitivity. The disturbance affects all sorts of sensitivity – touch, heat, cold, pain.
• Autonomous nerve disorders of the skin – blood circulation, sweating, temperature regulation.
• Disturbed visceral sensitivity.
• Disturbed proprioceptive sensitivity. Signals from muscles, joint capsules, tendons and skin to the cerebellum are blocked or distorted.
• Disturbances of the autonomous regulation of heart, lungs, gastrointestinal system, urogenital system.

A common feature of all polyneuropathies is that function loss is proportional to the length of the peripheral nerve. The sensitivity loss for all modes is thus greater, the more peripheral the recording. This rule also applies to proprioceptive disorders, vegetative disorders, and muscle paresis.

According to the general rule above, the earliest signs of a polyneuropathia should be traced in the outmost periphery of the nervous system. The simplest clinical application is to examine the the nervous functions of the big toe, which is served by the longest nerves of the body. The proprioceptive receptors are plenty around joints. These prerequisites provide the rationale for testing the vibratory sense in the phalango-interphalangeal (PIP) joint of the big toe.

The vibratory sense is thought to be conducted along (or parallel to) the proprioceptive tracts. The tuning-fork provides a simple and swift tool for the testing of the vibratory sense. The tuning-fork, shanks loaded, should vibrate at 64 hertz. The loading of the shanks is necessary for giving:

• Vibration strength.
• Vibration duration.
• Assessable disappearance of vibration.

The tuning-fork is switched on with the reflex hammer in order to avoid clinking overtones. The tuning-fork is then placed on the breastbone of the patient for co-ordinating compliance.

After starting, the tuning-fork is gripped between thumb and index-finger with the shaft propped to the peripheral PIP joint of the index. This grip enables the examiner to monitor the strength of vibration.

The tuning-fork is applied against the PIP joint of the big toe. The patient is asked whether he feels any vibration. If so, the tuning-fork is kept steady, and the patient is asked to report when the vibration disappears. In cases of defective vibration sense, the function is also tested over the malleolus, the patella, and the crista iliaca ventralis for level diagnosis of function loss.

The vibration disappears earlier in the PIP joint of the big toe than in the index finger, even in young and healthy probands. The vibratory sense declines with age. The border between polyneuropathia and healthy aging is difficult to determine. The rule of thumb is that index finger and the side protuberances of the ankle (malleoli) are equally sensitive to vibration.

It should be emphasized that biothesiometry provides quantitate information on vibration sensitivity. However, the tuning-fork appears to be the simplest and swiftest tool providing a semi-quantititave assessment of possible polyneuropathia in for example diabetes mellitus and vitamin B12 deficiency.

Reference

Holmberg CG, Jönemar B, Nordén Å, Stålberg K-G, Ktryding N. Methylmalonic acid excretion and serum vitamin B12. Scand J Haematol 1966; 2:399-403.

Updated juli 25, 2000