Christopher J Thompson

Disorders of Water Homeostasis in Neurosurgical Patients

CONTEXT Disorders of water balance are common in neurosurgical patients and usually manifest as hypo- or hypernatremia. They are most commonly seen after subarachnoid hemorrhage, traumatic brain injury, with intracranial tumors, and after pituitary surgery. SETTING We reviewed the experience of endocrine evaluation and management of disorders of salt and water balance in a large cohort of inpatients attending the national neurosciences referral centre in Dublin, Ireland, and compared this experience with findings from other studies. PATIENTS The study group included unselected neurosurgical patients admitted to our centre and requiring endocrine evaluation. INTERVENTIONS We conducted investigations to determine the underlying mechanistic basis for disorders of salt and water balance in neurosurgical patients and treatment to restore normal metabolism. MAIN OUTCOME MEASURES Morbidity and mortality associated with deranged salt and water balance were measured. RESULTS The underlying pathophysiology of disordered water balance in neurosurgical patients is complex and varied and dictates the optimal therapeutic approach. CONCLUSIONS A systematic and well-informed approach is needed to properly diagnose and manage disorders of salt and water balance in neurosurgical patients.

Osteoprotegerin and biomarkers of vascular inflammation in type 2 diabetes

Osteoprotegerin (OPG), receptor activator for nuclear factor kappa beta ligand (RANKL) and tumour necrosis factor–related apoptosis‐inducing ligand (TRAIL) are newly discovered members of the tumour necrosis factor‐alpha receptor superfamily. While their role in bone metabolism is well described, their function within the vasculature is poorly understood. OPG inhibits vascular calcification in vitro and high serum levels have been demonstrated in type 2 diabetes, but serum RANKL and TRAIL and their potential correlation with well‐established biomarkers of subclinical vascular inflammation such as high‐sensitivity C‐reactive protein (hsCRP) and interleukin‐6 (IL‐6) have not been described.

Central pontine myelinolysis complicating treatment of the hyperglycaemic hyperosmolar state

Abstract Central pontine myelinolysis (CPM) is well recognized to occur in a variety of clinical settings, but particularly following rapid correction of severe hyponatraemia. The development of CPM as a result of rapid shifts in plasma osmolality during the treatment of the hyperglycaemic hyperosmolar state (HHS) has hitherto been described in only one case. We report a second case in which this complication occurred in association with treatment of the HHS. The patient was a 49-year-old woman who presented to another hospital with drowsiness and a plasma glucose of 106 mmol/L. Her admission plasma sodium was 135 mmol/L. She received treatment with intravenous insulin and 0.9% normal saline, and there was a rapid drop in plasma glucose by 60 mmol/L within 6 h, which was associated with a rebound rise of plasma sodium to 159 mmol/L. Her plasma glucose and sodium were later stabilized. When the patient was transferred to our hospital a few days later, she was noted to have flaccid quadraparesis and pseudobulbar palsy. A magnetic resonance imaging scan revealed a pontine lesion consistent with CPM. She made a gradual recovery over several months with intensive rehabilitation and eventually returned to near normal functional capacity. This is the second case report in the literature of CPM complicating the management of HHS and highlights the importance of the judicious and measured correction of hyperglycaemia and the appropriate management of fluid replacement and electrolyte balance when treating this condition.

Osteoprotegerin is higher in peripheral arterial disease regardless of glycaemic status.

INTRODUCTION Peripheral arterial disease (PAD) and type 2 diabetes mellitus (DM) are both associated with excessive vascular calcification and elevated levels of inflammatory markers IL-6 and hsCRP. The recently identified Osteoprotegerin(OPG)/RANKL/TRAIL pathway has been implicated in vascular calcification, but data on levels in PAD and effect of co-existent DM are lacking. MATERIALS AND METHODS 4 groups of patients were recruited - 26 with PAD and DM, 35 with DM alone, 22 with PAD alone, and 21 healthy individuals. Serum OPG, RANKL, TRAIL, hsCRP and IL-6 were measured using commercial ELISA assays. Presence and severity of PAD was defined using ankle brachial index (ABI). RESULTS Serum OPG (7.4±0.3 vs.5.8±0.2 pmol/l, p<0.0001), TRAIL (95.5±5.2 ng/ml vs. 76.2±4.4 ng/ml, p=0.006), hsCRP (2.6±0.3 vs. 1.8±0.3 mg/l, p=0.048), and IL-6 (4.1±0.4 vs. 2.9±0.4 pg/ml, p=0.06) were higher in patients with PAD. There was no difference in RANKL. Only OPG was significantly higher in PAD and DM (7.2±0.3 pmol/l) and PAD alone (7.7±0.4 pmol/l) compared to DM only (5.8±0.3 pmol/l) and healthy controls (5.6±0.4 pmol/l), p<0.01, but OPG was no higher in those with DM plus PAD versus those with PAD alone (p<0.3). Only OPG was associated with PAD severity, correlating negatively with ABI (r=-0.26, p=0.03), independent of age, gender, glycaemic status, hsCRP and IL-6. CONCLUSIONS PAD is associated with higher serum OPG, regardless of the co-existence of DM. This finding, in addition to its correlation with severity of PAD, suggests that OPG may be a novel marker for the presence and severity of PAD, possibly by reflecting the degree of underlying vascular calcification.

A comparison of osteoprotegerin with adiponectin and high-sensitivity C-reactive protein (hsCRP) as a marker for insulin resistance

OBJECTIVE Insulin resistance (IR) is associated with low adiponectin and elevated high sensitivity C-reactive protein (hsCRP). Osteoprotegerin (OPG) has been shown to be elevated in type 2 diabetes, but whether it reflects underlying IR is unclear. We aimed to compare the ability of serum OPG with adiponectin and hsCRP to act as a marker for IR in individuals with normal and abnormal glucose tolerance. MATERIALS/METHODS 115 men underwent a 75 g oral glucose tolerance test. OPG, hsCRP and adiponectin were measured using ELISA. IR was assessed using the homeostasis model assessment of insulin resistance (HOMA-IR). RESULTS Men with abnormal glucose tolerance (n=38) were older (58.3±11.2 vs 47.3±11.4 years, P<.001), had higher body mass index (BMI) (31.1±2.9 vs 27.9±3.2 kg/m(2), P<.001) and were more insulin resistant (median (I.Q.) HOMA-IR 5.88 (3.38) vs 1.13 (1.14), P<.001) than those with normal glucose tolerance (n=77). After adjustment for age and BMI, OPG (6.28 (2.32) vs 5.16 (1.86) pmol/L, P<.001) and hsCRP (2.07 (5.47) vs 0.78 (1.05) mg/L, P<.001) were higher and adiponectin (3.02±1.17 vs 4.78±2.38 μg/mL, P<.001) was lower in those with AGT. After adjustment for age and BMI, adiponectin (r=-0.317, P<.001) and hsCRP (r=0.318, P<.001), but not OPG (r=0.126, P=.196) correlated with HOMA-IR. On multiple linear regression analysis, adiponectin and hsCRP but not OPG were independent predictors of HOMA-IR. CONCLUSIONS OPG is higher in individuals with abnormal glucose tolerance, but unlike adiponectin and hsCRP, does not correlate with HOMA-IR, suggesting its elevation within this cohort of individuals is due to factors other than insulin resistance.

MANAGEMENT OF ENDOCRINE DISEASE: Neuroendocrine surveillance and management of neurosurgical patients

Advances in the management of traumatic brain injury, subarachnoid haemorrhage and intracranial tumours have led to improved survival rates and an increased focus on quality of life of survivors. Endocrine sequelae of the acute brain insult and subsequent neurosurgery, peri-operative fluid administration and/or cranial irradiation are now well described. Unrecognised acute hypopituitarism, particularly ACTH/cortisol deficiency and diabetes insipidus, can be life threatening. Although hypopituitarism may be transient, up to 30% of survivors of TBI have chronic hypopituitarism, which can diminish quality of life and hamper rehabilitation. Patients who survive SAH may also develop hypopituitarism, though it is less common than after TBI. The growth hormone axis is most frequently affected. There is also accumulating evidence that survivors of intracranial malignancy, who have required cranial irradiation, may develop hypopituitarism. The time course of the development of hormone deficits is varied, and predictors of pituitary dysfunction are unreliable. Furthermore, diagnosis of GH and ACTH deficiency require dynamic testing that can be resource intensive. Thus the surveillance and management of neuroendocrine dysfunction in neurosurgical patients poses significant logistic challenges to endocrine services. However, diagnosis and management of pituitary dysfunction can be rewarding. Appropriate hormone replacement can improve quality of life, prevent complications such as muscle atrophy, infection and osteoporosis and improve engagement with physiotherapy and rehabilitation.

Low-dose hydrocortisone replacement is associated with improved arterial stiffness index and blood pressure dynamics in severely adrenocorticotrophin-deficient hypopituitary male patients

OBJECTIVE Increased cardiovascular and cerebrovascular morbidity and mortality in hypopituitary subjects may be linked to inappropriate glucocorticoid exposure; however, the pathophysiology remains unclear. We aimed to examine the effect of three commonly prescribed hydrocortisone (HC) regimens on vascular risk factors. DESIGN An open crossover study randomising ten hypopituitary men with severe adrenocorticotrophic hormone deficiency to three HC dose regimens: dose A (20mg mane and 10mg tarde), dose B (10mg mane and 10mg tarde) and dose C (10mg mane and 5mg tarde). METHODS Following 6 weeks on each regimen, participants underwent 24-h serum cortisol sampling, 24-h ambulatory blood pressure (BP) measurements, calculation of the Ambulatory Arterial Stiffness Index (AASI), oral glucose tolerance testing and fasting serum osteoprotegerin (OPG) sampling. RESULTS There were no differences in 24-h BP between dose regimens and controls; however, low-dose HC replacement (dose C) was associated with the lowest AASI, indicating a less stiff arterial tree (P<0.05) compared with the other dose regimens. Loss of the physiologic nocturnal BP dip was more common in higher HC replacement regimens, although only significant for dose B compared with dose C (P=0.03). Twenty per cent of patients had abnormal glucose tolerance, but this was unrelated to dose regimen. OPG correlated strongly with 24-h BP in those on dose A only (r=0.65, P=0.04). CONCLUSION Currently prescribed HC replacement doses do not result in significant differences in absolute BP levels or improvements in insulin sensitivity. However, lower HC doses may result in lower arterial stiffness and a more physiological nocturnal BP dip. Long-term studies are required to confirm these findings and evaluate their impact on vascular morbidity in this patient group.

Hyponatraemia – presentations and management

ABSTRACT Hyponatraemia is the most common electrolyte disturbance encountered in clinical practice. It is associated with significant morbidity and mortality, thus appropriate investigation and treatment is essential. Hyponatraemia presents with a spectrum of clinical presentations ranging from no symptoms to life-threatening neurological sequelae. Hyponatraemia has multiple aetiologies and distinguishing the underlying aetiology facilitates appropriate treatment. This review provides an overview of the presentations and approaches to management of this common clinical condition.