Effect of magnesium on nerve conduction velocity during regular dialysis treatment

Hypomagnesemia in Continuous Ambulatory Peritoneal Dialysis Patients Dialyzed with a Low-Magnesium Peritoneal Dialysis Solution

Objective

Previous studies have shown a decrease in serum magnesium (Mg) concentration when continuous ambulatory peritoneal dialysis (CAPD) patients previously maintained on a 1.0 –1.2 mEq/L Mg peritoneal dialysis solution (PDS) were dialyzed with a 0.5 mEq/L Mg PDS. However, the prevalence of hypomagnesemia in CAPD patients dialyzed with low-Mg PDS is unknown.

Design

A retrospective study to determine the prevalence of hypomagnesemia and the factors associated with its occurrence in CAPD patients dialyzed using a 0.5 mEq/L Mg PDS.

Setting

A CAPD unit in a large Veterans Affairs Hospital.

Patients

All our CAPD patients (33) enrolled over a 52month period.

Results

All patients had serum magnesium levels higher than 1.25 mEq/L prior to use of low-Mg PDS. Hypomagnesemia (serum Mg < 1.25 mEq/L) developed in 21/33 patients (64%) when a 0.5 mEq/L Mg PDS was employed. Hypomagnesemia developed a mean of 8.2 months after beginning treatments. The duration of dialysis and the number of episodes of peritonitis did not differ between patients with and those without hypomagnesemia. Serum albumin levels were significantly lower in patients with hypomagnesemia (2.5±0.12 g/dL vs 3.2±0.12, p < 0.01). Magnesium supplements were given to 13 patients; following this therapy, serum magnesium values became normal.

Conclusions

CAPD patients dialyzed with a 0.5 mEq/L Mg PDS may develop a considerable fall in serum magnesium level and may require magnesium supplements in order to restore normal serum values.

Prevalence and predictors of peripheral neuropathy in nondiabetic children with chronic kidney disease

INTRODUCTION

This study sought to determine the prevalence and predictors of peripheral neuropathy in nondiabetic children with chronic kidney disease (CKD).

METHODS

Fifty-one consecutive normally nourished children, 3-18 years of age, with CKD stages IV and V of nondiabetic etiology were enrolled from May to December 2012. Nerve conduction studies were performed in 50 children. Blood samples were analyzed for the biochemical parameters, trace elements, and micronutrients.

RESULTS

The prevalence of peripheral neuropathy in our cohort was 52% (95% confidence interval 37.65, 66.34). The majority (80.8%) of the children had axonal neuropathy, and 11.5% had demyelinating neuropathy. Isolated motor neuropathy was identified in 92.3% of the children, and sensorimotor neuropathy was identified in 7.6%. The significant risk factors associated with peripheral neuropathy were older age, low serum copper, and dialysis therapy.

DISCUSSION

Electrodiagnostic studies should be performed in children with CKD to assess for peripheral neuropathy for the purpose of optimizing medical care. Muscle Nerve 57: 792-798, 2018.

Hypomagnesemia in hemodialysis patients: role of proton pump inhibitors

BACKGROUND

Recent observations have associated hypomagnesemia with increased risk of cardiovascular morbidity and mortality in hemodialysis patients.

METHODS

We did a 3-month chart review of 62 chronic hemodialysis patients at a single US hospital. All were dialyzed using a dialysate [Mg] of 0.75-1.0 mEq/l. Patients were divided into two groups: hypomagnesemic (mean predialysis plasma [Mg] <1.5 mEq/l) and non-hypomagnesemic (mean predialysis plasma [Mg] ≥1.5 mEq/l).

RESULTS

All patients were male; mean age was 64.3 ± 8.7 years and the majority (73%) diabetic. 24 patients (39%) had hypomagnesemia and 38 (61%) were not hypomagnesemic. There were no significant differences between the two groups in age, diabetes status, blood pressure, duration of dialysis, plasma calcium, phosphorus, albumin, intact parathyroid hormone (PTH), dialysis adequacy (Kt/V), or dietary protein intake (as estimated by normalized protein catabolic rate, nPCR). However, use of proton pump inhibitors (PPIs) was significantly associated with hypomagnesemia (plasma [Mg] 1.48 ± 0.16 mEq/l in the PPI group vs. 1.65 ± 0.26 mEq/l in the non-PPI group, p = 0.007). Adjustment for age, diabetes status, duration of dialysis, plasma albumin, Kt/V, nPCR, and diuretic use did not affect the association between PPI use and hypomagnesemia.

CONCLUSIONS

Use of PPIs in patients dialyzed using a dialysate [Mg] of 0.75-1.0 mEq/l is associated with hypomagnesemia. We suggest monitoring plasma [Mg] in patients taking PPIs, with discontinuation of the medication if possible and/or adjustment of dialysate [Mg] to normalize plasma [Mg].

Transient changes of sensory nerve functions in uraemia

The neurophysiological parameters (conduction velocity, amplitude and rise time of the compound action potential) of two sensory nerves of the lower limb (N. suralis and peronaeus superficialis) were determined bilaterally in five patients. Measurements were carried out at least twice in each subject during a time of great metabolic change. Two patients were recovering from acute renal failure (a single haemodialysis had to be performed on one of them) and three were under chronic maintenance haemodialysis. In the case of the haemodialysis patients, measurements were performed on two successive days, before and after one haemodialysis session. All the neurophysiological parameters showed significant improvement in successive measurements. In one patient the follow-up after acute renal failure revealed a delayed deterioration of the nerve functions, but after one year the values were normal. From the results it seems probable that an acute metabolic disturbance may cause transient inhibition of nerve functions without morphological changes in the nerve fibres.

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.

Influence of magnesium deficiency on concentration of calcium in soft tissue of uremic rats

The influence of magnesium (Mg) deficiency on the concentration of calcium (Ca) in the aorta, heart, and kidney was evaluated in uremic rats. A total of 32 rats were randomly assigned to two groups: one group made uremic by the 5/6 nephrectomy method, and the other serving as sham-operated controls. Both groups were randomly assigned to two subgroups: one group given a Mg-deficient diet and the other fed a Mg-supplemented diet. After 12 weeks on the regimen, all animals were sacrificed. In Mg-supplemented uremic rats, the concentration of Ca in the aorta was higher than in Mg-supplemented control rats. The concentration of Ca in the aorta was further increased in Mg-deficient uremic rats. The concentrations of Ca in the heart and the kidney were also increased in Mg-deficient uremic rats, as compared with Mg-supplemented uremic rats. The concentration of Mg was decreased in the aorta and increased in the kidney of Mg-deficient rats. There was no significant influence of Mg deficiency on the concentration of phosphate in tissue. Results suggest that Mg deficiency in uremia may increase aortic calcification.

Effects of a magnesium-free dialysate on magnesium metabolism during continuous ambulatory peritoneal dialysis

While the use of magnesium-containing compounds is usually contraindicated in dialysis patients, the risk of toxicity from hypermagnesemia can be reduced by lowering the magnesium concentration in dialysate. We examined the effects of a magnesium-free dialysate on both serum magnesium level and the peritoneal removal rate of magnesium over 12 weeks in 25 stable patients undergoing continuous ambulatory peritoneal dialysis (CAPD). After 2 weeks, the serum magnesium level decreased from 2.2 to 1.9 mg/dL (0.9 to 0.8 mmol/L) (P less than .02) and the peritoneal removal rate increased from 66 to 83 mg/d (2.8 to 3.5 mmol/d) (P less than .05), with both values remaining stable thereafter. There was a strong association between these parameters (r = -0.62, P less than .05), suggesting that the serum magnesium level decreased as a result of the initial increased peritoneal removal rate. For an additional 4-week period, a subgroup of nine patients received magnesium-containing, phosphate binding agents instead of those containing only aluminum. During this phase, serum inorganic phosphorus was well controlled. The serum magnesium level increased only from 1.8 to 2.5 mg/dL (0.7 to 1.0 mmol/L) (P less than .05), due in great part to the concomitant 41% rise in peritoneal magnesium removal from 91 to 128 mg/d (3.8 to 5.3 mmol/d) (P less than .05). No toxicity was noted during the entire 16-week study period, nor did serum calcium change. Thus, serum magnesium levels remained within an acceptable range as magnesium-containing phosphate binders were given through the use of magnesium-free peritoneal dialysate.(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of conduction velocity in myelinated nerve fibers

This article reviews the determinants of conduction velocity in myelinated nerve fibers. For fibers exhibiting geometric similarity, conduction velocity is nearly proportional to diameter. However, in classes of geometrically similar fibers, myelin thickness and internode distance are linearly related to diameter. Therefore, it is not possible to assess the relative contributions of each of these factors. The relative effects of changes in each of these parameters on conduction velocity can be assessed from studies on fibers representing different similarity classes or from theoretical parametric studies. These studies show that for a fixed axon diameter, conduction velocity increases with myelin thickness. For a fixed total fiber diameter, there is an optimal ratio of axon diameter to total fiber diameter (and therefore to myelin thickness) at which conduction velocity is maximized. Conduction velocity is dependent on internode distance, with a broad maximum centered around the value observed in normal peripheral fibers. Conduction velocity is also dependent on temperature and the properties of the axonal milieu. Thus, the conduction speed of any given fiber reflects a number of parameters and is not determined by any single structural characteristic.

Neuropsychiatric symptomatology with chronic renal insufficiency in the stage of compensated and decompensated retention. II. Peripheral nerve disturbances

80 strictly selected patients with chronic renal insufficiency with plasma creatinine values of 1.4-14.5 mg% were examined for clinical and electrophysiological signs of nephrogenic polyneuropathy. The motor symptoms complained of were cramps in 43.8% of the patients, "restless leggs" in 18.7%, muscular twitchings in 12.5%. It was emphasized that the first two symptoms do not always indicate the presence of polyneuropathy. 30% complained of paresthesias, 5% of "burning feet". The most frequent clinical finding was the impairment of vibration sense in the feet in 37.5% followed by diminshed appreciation of passive movement of the toes in 30%, weakening or absence of the ankle jerk in 23.8% and finally, weakening of the patellar reflex in 5%...

Effect of chronic renal failure, dialysis and transplantation on motor nerve conduction velocity in children

Ulnar and peroneal motor nerve conduction volocities (MNCVs) were measured in 47 children in a dialysis-transplantation program. Mean peroneal MNCV was significantly decreased from normal in children with mild renal failure (serum creatinine concentration, 1.5 to 2.9 mg/dl), whereas ulnar MNCV was significantly decreased only when the serum creatinine value was at least 9 mg/dl. Both ulnar and peroneal MNCVs remained unchanged during long-term hemodialysis or peritoneal dialysis; however, after individual dialyses ulnar MNCV increased. After renal transplantation ulnar MNCV returned to normal within a year and peroneal MNCV within 3 years. Before dialysis was required and during long-term dialysis most plasma magnesium values were elevated; ionized calcium activity was decreased in about 50% of determinations. After transplantation and the concentration of divalent cations rapidly returned to normal. These children differed from adults studied in that (a) there was no correlation between severity of renal failure and MNCV, (b) long-term dialysis did not improve MNCV and (c) peroneal velocities did not recover for 3 years after transplantation.