Transient changes of sensory nerve functions in uraemia

Neuromuscular disease in the dialysis patient: an update for the nephrologist

Neuromuscular disease is an extremely common complication of end-stage kidney disease (ESKD), manifesting in almost all dialysis patients, and leading to weakness, reduced exercise capacity, and disability. Recent studies have suggested that hyperkalemia may underlie the development of neuropathy. As such, maintenance of serum K(+) within normal limits between periods of dialysis in ESKD patients manifesting early neuropathic symptoms may reduce neuropathy development and progression. For patients with more severe neuropathic syndromes, increased dialysis frequency or a switch to high-flux dialysis may prevent further deterioration, while ultimately, renal transplantation is required to improve and restore nerve function. Exercise training programs are beneficial for ESKD patients with muscle weakness due to neuropathy or myopathy, and are capable of improving exercise tolerance and quality of life. Specific treatments have recently been evaluated for symptoms of autonomic neuropathy, including sildenafil for impotence and midodrine for intra-dialytic hypotension, and have been shown to be effective and well tolerated. Other important management strategies for neuropathy include attention to foot care to prevent callus and ulceration, vitamin supplementation, and erythropoietin. Treatment with membrane-stabilizing agents, such as amitryptiline and gabapentin, are highly effective in patients with painful neuropathy.

Altered motor nerve excitability in end-stage kidney disease

Although multiple toxins have been implicated in the development of uraemic neuropathy, no causative agent has been identified. In the present study, the excitability properties of lower limb motor nerves in patients with end-stage kidney disease treated with haemodialysis were measured before, during and after a standard 5 h haemodialysis session, in an attempt to explore the pathophysiology of uraemic neuropathy. Compound muscle action potentials were recorded from tibialis anterior and extensor digitorum brevis, following stimulation of the common peroneal nerve in 14 patients. Measures of excitability were assessed in relation to changes in serum levels of potential neurotoxins, including potassium, calcium, urea, uric acid, parathyroid hormone and beta-2-microglobulin. Before dialysis, measures of nerve excitability were significantly abnormal in the patient group for axons innervating tibialis anterior and extensor digitorum brevis, consistent with axonal depolarization: refractoriness was increased and superexcitability and depolarizing threshold electrotonus were reduced. Pre-dialysis excitability abnormalities were strongly correlated with serum K+. Correlation was also noted between the severity of symptoms and excitability abnormalities. Haemodialysis normalized the majority of nerve excitability parameters. In conclusion, lower limb motor axons in uraemic patients are depolarized before dialysis. The correlation between serum K+ and excitability measures indicates that hyperkalaemia is primarily responsible for uraemic depolarization, and a likely contributing factor to the development of neuropathy.

Neurophysiologic parameters and symptoms in chronic renal failure

We studied: (1) the sensitivity of various neurophysiologic parameters in the diagnosis of uremic polyneuropathy, (2) the relationship between subjective symptoms and neurophysiologic parameters, and (3) the effect of a single hemodialysis on the neurophysiologic parameters in 21 patients undergoing hemodialysis. The following parameters were studied: sensory and motor nerve conduction, including F-wave parameters; vibration detection thresholds; and thermal thresholds. The clinical findings and subjective symptoms were studied using a standardized questionnaire. The most sensitive parameters in the diagnosis of uremic neuropathy were F-wave parameters from lower limbs, vibration detection thresholds from the feet, and the sural nerve sensory action potential amplitude. The nerves from the upper extremities on the side of the fistula should not be used in the diagnosis of uremic polyneuropathy due to numerous mild local nerve lesions. The positive neuropathic symptoms correlated with quantitative vibratory detection thresholds and sensory nerve conduction studies, especially the amplitude of the sensory nerve action potential in the sural nerve. We found no significant change in any of the neurophysiologic parameters following a single hemodialysis session.

Effects of haemodialysis on heart rate variability in chronic renal failure

The influence of haemodialysis (HD) on the heart rate variability (HRV) was investigated in nine non-diabetic patients on maintenance haemodialysis. The R-R intervals were measured in recordings during spontaneous quiet breathing and during controlled deep breathing before and after a single HD session. The HRV was expressed as the standard deviation of the mean R-R interval in 3 min ECG recordings. Heart rate variability is the irregularity in the heart rate mainly caused by autonomic control mechanisms. The long-term HRV during quiet breathing was statistically significantly (p less than 0.05) higher after the HD than before. The HRV in the intermediate frequency range of 0.075-0.125 Hz was also significantly increased by the HD. This suggests that some metabolic agents interfering with the heart rate regulation are removed by the haemodialysis, and as a result a better function of the autonomic cardiac control is achieved in uraemic patients.

Quantitative vibration perception thresholds in patients under prolonged antiepileptic treatment

Quantitative vibration perception threshold (VPT) measurements were performed on 134 healthy subjects and 147 epileptics undergoing prolonged (more than one year) antiepileptic treatment, 28 patients received diphenylhydantoin, 71 carbamazepine and 11 some other drug. 37 subjects received a combination of drugs, which included diphenylhydantoin and/or carbamazepine. VPT was measured quantitatively at the dorsum of the right foot with a device vibrating at 100 Hz. The mean of the four successive threshold values was calculated. VPTs of the epileptic groups treated with diphenylhydantoin, carbamazepine or combined medication were all significantly (P less than 0.001) higher than those of the control group. The group receiving other medication showed no difference in this respect. The percentage of patients with abnormal thresholds was about the same (10-16) in the epileptic groups. An exception was the group taking other medication, in which no abnormal VPTs were found. It is suggested that such quantitative measurement may be a useful screening method for detecting dysfunction in the peripheral nervous system due to prolonged antiepileptic treatment. It will, however, be necessary to test the clinical validity of the method for diagnosing manifest or subclinical polyneuropathies.

Does transient blocking of axonal conduction occur in uraemic neuropathy?

In uraemic and other patients with neuropathies, motor unit spike intervals were analysed using a special computer program to detect prolonged intervals of twice the normal duration, so-called "double intervals." These may have different causes--trigger failure, double discharge, or a transient fall in the firing rate of coactive motor units. There was not sufficient evidence that transient conduction blockings will occur in the main axon in uraemic neuropathies.