In vivo estimation of optic nerve sheath stiffness using noninvasive MRI measurements and finite element modeling

The optic nerve sheath (ONS) is biomechanically important. It is acted on by tension due to ocular movements, and by fluid shifts and/or alterations in intracranial pressure (ICP) in human disease, specifically in pathologies leading to intracranial hypertension. It has also been hypothesized that the ONS is acted on by altered ICP in astronauts exposed chronically to microgravity. However, a non-invasive method to quantify ONS biomechanical properties is not presently available; knowledge of such properties is desirable to allow characterization of the biomechanical forces exerted on the optic nerve head and other ocular structures due to the ONS. Thus, the primary objective of this study was to characterize the biomechanical properties (stiffness) of the human ONS in vivo as a necessary step towards investigating the role of ICP in various conditions, including Spaceflight Associated Neuro-ocular Syndrome (SANS). We acquired non-invasive magnetic resonance imaging (MRI) scans of ostensibly healthy subjects (n = 18, age = 30.4 ± 11.6 [mean ± SD] years) during supine and 15-degree head-down-tilt (HDT) postures, and extracted ONS contours from these scans. We then used finite element modeling to quantify ONS expansion due to postural changes and an inverse approach to estimate ONS stiffness. Using this non-invasive procedure, we estimated an in vivo ONS stiffness of 39.2 ± 21.9 kPa (mean ± SD), although a small subset of individuals had very stiff ONS that precluded accurate estimates of their stiffness values. ONS stiffness was not correlated with age and was higher in males than females.

Delirium associated with sertraline, a case report

Introduction

Delirium is a clinical entity consisting of acute loss of consciousness, with attention deficit and fluctuating evolution. Antidepressive medication can cause these symptoms or worsen them.

Case report

We report the case of a 84-year-old blind female who was diagnosed of delirium in relation to intoxication with sertraline. The patient was admitted into a short-stay psychiatric unit for three days. She presented behavioural disturbances consisting in auto and heteroaggressive behaviour, altered consciousness and visual hallucinations (rocks, turtles). When dosage of sertraline was doubled from 50 mg/day to 100 mg/day visual hallucinations started. There were not other medical causes found, so sertraline was suspended, achieving clinical improvement.

Discussion

This case report shows how a patient with antidepressive treatment can display delirium. The three main causes of delirium that are infections, side effects and methabolic syndrome.

Conclusions

In the case of treating a patient with delirium, the presence of previous illness has to be investigated. It is indispensable to describe the presence of previous illness, medication and recent changes of the dosages in the medical history in a patient with Sertraline.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Prolactine borderline, a case report

Introduction

It is known that antipsychotic drugs can increase prolactinaemia, we report a case in which the use of aripiprazole after treatment with paliperidone helped regaining normality levels.

Case report

During treatment with PALiperidone12 mg/day the patient, a 27-year-old female diagnosed with borderline personality disorder, developed hyperprolactinaemia with galactorrhea and menstrual disorders. During hospitalization, aripiprazole is introduced while paliperidone is progressively decreased. Antipsychotic were prescribed because delusions of reference and auditory pseudo-hallucinations arose suddenly in a woman without history of previous psychotic breaks. Before treatment with aripiprazole, prolactinaemia was 156,96 ng/mL (pregnancy test was negative) and after stopping, paliperidone was 23,60 ng/mL.

Discussion

If hyperprolactinaemia symptoms appeared (galactorrhea…), aripiprazole is a good option if antipsychotic treatment is required. In this case, paliperidone was decreased slowly, while aripiprazole was increased, until minimum effective dose was reached.

Conclusions

Hyperprolactinaemia is a common side effect in antipsychotic treatments and if symptoms appeared aripiprazole is a good option.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Efficacy of a sclerostin antibody compared to a low dose of PTH on metaphyseal bone healing

We compared the effect of a sclerostin antibody to that of a clinically relevant dose of parathyroid hormone (PTH) in a rat model for metaphyseal bone healing. Screws of steel or poly methyl methacrylate (PMMA) were inserted bilaterally into the proximal tibia of young male rats. During 4 weeks the animals then received injections of either phosphate buffered saline (control), sclerostin antibody (25 mg/kg, twice weekly) or PTH (5 µg/kg, daily). The healing response around the screws was then assessed by mechanical testing and X-ray microtomography (µCT). To distinguish between effects on healing and general effects on the skeleton, other untraumatized bone sites and serum biomarkers were also assessed. After 4 weeks of treatment, PTH yielded a 48% increase in screw pull-out force compared to control (p = 0.03), while the antibody had no significant effect. In contrast, the antibody increased femoral cortical and vertebral strength where PTH had no significant effect. µCT showed only slight changes that were statistically significant for the antibody mainly at cortical sites. The results suggest that a relatively low dose of PTH stimulates metaphyseal repair (screw fixation) specifically, whereas the sclerostin antibody has wide-spread effects, mainly on cortical bone, with less influence on metaphyseal healing.

Renal stone risk in a simulated microgravity environment: impact of treadmill exercise with lower body negative pressure

PURPOSE

Prolonged exposure to microgravity during spaceflight causes metabolic changes that increase the risk of renal stone formation. Studies during the Gemini, Apollo, Skylab and Shuttle missions demonstrated alterations in renal function, fluid homeostasis and bone resorption that result in increased urinary supersaturation of calcium oxalate, brushite, sodium urate and uric acid. Developing countermeasures to increased urinary supersaturation is an important priority as the duration of space missions increases.

MATERIALS AND METHODS

A total of 11 sets of identical twins remained on 6-degree head down, tilt bed rest for 30 days to simulate prolonged microgravity. One twin per pair was randomly selected to exercise while supine in a lower body negative pressure chamber 6 days weekly for 40 minutes, followed by 5 minutes of resting lower body negative pressure at 50 mm Hg. The other twin served as a nonexercise control. Pressure in the exercise lower body negative pressure chamber (52 to 63 mm Hg) was adjusted to produce footward forces equivalent to those for upright running on Earth at 1.0 to 1.2 x body weight. Pre-bed rest urinary stone risk profiles were done elsewhere after 5 days of a standardized diet, consisting of 170 mEq sodium, 1,000 mg calcium, 0.8 gm/kg animal protein and 2,500 kcal, and then throughout the bed rest and recovery phases of the protocol.

RESULTS

A significant increase in urinary calcium after just 1 week of bed rest was noted in the nonexercise control group (p = 0.001). However, no such increase was noted in the exercise group. Brushite supersaturation increased significantly from bed rest in each group, although the increase was significantly higher in the nonexercise control group than in the exercise group (p = 0.006). Calcium oxalate supersaturation increased during bed rest in the exercise group (p = 0.004). It trended toward a higher level in the nonexercise control group, although this did not achieve significance (p = 0.055) Mean urine volume +/- SD was significantly higher in the nonexercise control group than in the exercise group at bed rest week 2 and at week 3 (2.01 +/- 0.21 vs 1.63 0.18 l and 2.03 +/- 0.22 vs 1.81 +/- 0.20, respectively). Urinary pH was significantly higher in the nonexercise control group than in the exercise group at week 1 and week 3 (6.62 +/- 0.7 vs 6.49 +/- 0.5 and 6.58 +/- 0.6 vs 6.49 +/- 0.8, respectively, p = 0.01).

CONCLUSIONS

Bed rest significantly alters the urinary environment to favor calculous formation. Lower body negative pressure chamber treadmill exercise offers some protection against increases in stone risk during simulated microgravity, particularly with regard to the risks of hypercalciuria and brushite stone formation. The use of lower body negative pressure to augment aerobic exercise in space may decrease the risk of stone formation in astronauts. Adjunct measures, including aggressive hydration and alkalinization therapy, should be considered.

Genetic heritability of urinary stone risk in identical twins

PURPOSE

Quantitative measurements of urinary parameters are valuable clinical tools for predicting the risk of nephrolithiasis. To our knowledge no previous studies have evaluated the heritability of urinary stone risk in identical twins. Because these individuals share identical genetics, the R defined by their phenotypic data are theoretically equal to the entire population H2.

MATERIALS AND METHODS

A total of 12 sets of healthy homozygous twins, including 4 males and 8 females for a total of 24 individuals, with a mean age of 25.9 years (range 21 to 36) volunteered for this study. All subjects provided informed written consent before assessment. Urinary stone risk profiles were done elsewhere on 2 consecutive days after 5 days of a standardized diet (170 mEq Na and 2500 kcal). Linear regression was performed on the data to determine R. Because identical twins were used, R was theoretically an estimate of H2.

RESULTS

Certain urinary stone risk markers were highly heritable, including urinary calcium (94%), oxalate (94%), citrate (95%), uric acid (96%) and brushite supersaturation (90%), as determined by genotype (H2 90% or greater). Uric acid supersaturation (58%) and urinary sodium (64%) had low degrees of heritability.

CONCLUSIONS

H2 is a measure of how much of the total variance in phenotype results from differences in genotype, as opposed to environmental differences. For example, an H2 of 95% for citrate suggests that genetic differences account for 95% of the variation in urinary citrate and environmental differences account for the remaining 5%. Therefore urinary calcium, oxalate and citrate are primarily determined by genotype, while environmental factors, particularly those that impact urine pH and urinary volume, may be increasingly important for determining uric acid supersaturation.

Paraspinal muscle vasculature contributes to posterolateral spinal fusion

STUDY DESIGN

Study of posterolateral fusions in a rabbit model.

OBJECTIVES

To characterize the contribution of paraspinal musculature to the healing of posterolateral spinal fusions in a rabbit model.

SUMMARY OF BACKGROUND DATA

Previous studies have demonstrated that successful spinal arthrodesis requires vascular ingrowth from adjacent decorticated bone. In other areas of the body, such as the tibia, vascular ingrowth from the surrounding musculature has also been shown to be important. The role of the surrounding paraspinal musculature in spinal fusions has yet to be assessed.

METHODS

Twenty-five New Zealand white rabbits underwent posterolateral spinal fusion. One side of the animals was treated with autograft alone and served as the control group. On the contralateral side, the autograft was contained within porous or nonporous barrier sheets. Following euthanization, high-resolution radiographs, CT scans, and histologic analyses were performed to assess fusion and characterize vascular ingrowth.

RESULTS

Using histologic evaluation, the fusion rate in the porous group was 90%, in the nonporous group 40%, and in the control group 55%. Vascular ingrowth was evident from the muscle through the porous sheet into the fusion mass.

CONCLUSIONS

These results support our hypothesis that the paraspinal musculature provides important vascular ingrowth into the fusion site. Use of a porous barrier sheet appears to improve fusion by preventing muscle interposition while allowing vascular ingrowth from surrounding muscle.