Neurologic complications of disorders of the adrenal glands

Paraneoplastic neurologic manifestations of neuroendocrine tumors

Neuroendocrine neoplasms (NENs) are a heterogeneous group of tumors arising from the transformation of neuroendocrine cells in several organs, most notably the gastro-entero-pancreatic system and respiratory tract. The classification was recently revised in the 5th Edition of the WHO Classification of Endocrine and Neuroendocrine Tumors. NENs can rarely spread to the central or peripheral nervous systems. Neurologic involvement is determined by the rare development of paraneoplastic syndromes, which are remote effects of cancer. Mechanisms depend on immunologic response to a tumor, leading to the immune attack on the nervous system or the production of biologically active ("functioning") substances, which can determine humoral (endocrine) effects with neurologic manifestations. Paraneoplastic neurologic syndromes (PNS) are immunologically mediated and frequently detected in small cell lung cancer but rarely seen in other forms of NEN. PNS and Merkel cell carcinoma is increasingly reported, especially with Lambert Eaton myasthenic syndrome. Endocrine manifestations are found in a wide spectrum of NENs. They can develop at any stage of the diseases and determine neurologic manifestations. Patient outcomes are influenced by tumor prognosis, neurologic complications, and the severity of endocrine effects.

Neurologic Complications of Endocrine Disorders

OBJECTIVE

This article provides an overview of the neurologic complications of the most prevalent endocrine disorders in adults with an emphasis on relevant neurologic symptoms, signs, and laboratory and neuroimaging findings.

LATEST DEVELOPMENTS

Although the mechanisms of many of the neurologic complications discussed here remain unclear, our understanding of the impacts of diabetes and hypothyroidism on the nervous system and muscle, including complications of rapid correction of chronic hyperglycemia, has advanced in recent years. Recent large studies have not demonstrated a convincing association between subclinical or overt hypothyroidism and cognitive decline.

ESSENTIAL POINTS

Neurologists must become familiar with the neurologic complications of endocrine disorders not only because they are common and treatable (and often reversible) but also because they may be iatrogenic, as is the case with adrenal insufficiency in the setting of long-term corticosteroid therapy.

Reversible Non-parkinsonian Bradykinesia with Impaired Frontal Lobe Function as the Predominant Manifestation of Adrenal Insufficiency

A 69-year-old Japanese man with a history of suprasellar surgery and irradiation developed bradykinesia and mild fatigue without muscle weakness, myalgia, pyramidal or extrapyramidal signs, parkinsonian symptoms, or ataxia. An endocrinological work-up revealed anterior hypopituitarism associated with secondary adrenal insufficiency. Higher brain function tests indicated an impaired frontal lobe function. The patient's bradykinesia, fatigue, and frontal lobe dysfunction improved within 2 weeks after the initiation of corticosteroid replacement therapy. To our knowledge, this is the first reported case of adrenal insufficiency manifesting as non-parkinsonian bradykinesia. Physicians should consider reversible non-parkinsonian bradykinesia associated with frontal lobe dysfunction as an unusual manifestation of adrenal insufficiency.

Endocrine Emergencies With Neurologic Manifestations

PURPOSE OF REVIEW

This article provides an overview of endocrine emergencies with potentially devastating neurologic manifestations that may be fatal if left untreated. Pituitary apoplexy, adrenal crisis, myxedema coma, thyroid storm, acute hypercalcemia and hypocalcemia, hyperglycemic emergencies (diabetic ketoacidosis and hyperglycemic hyperosmolar state), and acute hypoglycemia are discussed, with an emphasis on identifying the signs and symptoms as well as diagnosing and managing these clinical entities.

RECENT FINDINGS

To identify the optimal management of endocrine emergencies, using formal clinical diagnostic criteria and grading scales such as those recently proposed for pituitary apoplexy will be beneficial in future prospective studies. A 2015 prospective study in patients with adrenal insufficiency found a significant number of adrenal crisis-related deaths despite all study patients receiving standard care and being educated on crisis prevention strategies, highlighting that current prevention strategies and medical management remain suboptimal.

SUMMARY

Early diagnosis and prompt treatment of endocrine emergencies are essential but remain challenging because of a lack of objective diagnostic tools. The optimal management is also unclear as prospective and randomized studies are lacking. Additional research is needed for these clinical syndromes that can be fatal despite intensive medical intervention.

Programmed symptoms: disparate effects united by purpose

Central sensitivity syndromes (CSS) share features of similar multiple symptoms, virtually unknown mechanisms and lack of effective treatments. The CSS nomenclature was chosen over alternatives because it focused on a putative physiological mechanism of central sensitization common to disorders such as fibromyalgia, irritable bowel syndrome, vulvodynia and temporomandibular disorder. Increasing evidence from multiple biological systems suggests a further development. In this new model central sensitization is part of a ensemble that includes also the symptoms of widespread pain, fatigue, unrefreshing sleep and dyscognition. The main feature is an intrinsic program that produces this ensemble to guide behavior to restore normal function in conditions that threaten survival. The well known “illness response” is a classic example that is triggered in response to the specific threat of viral infection. The major leap for this model in the context of CSS is that the symptom complex is not a reactive result of pathology, but a purposeful feeling state enlisted to combat pathology. Once triggered, this state is produced by potential mechanisms that likely include contributions of the peripheral and central immune systems, as well as stress response systems such as the autonomic system and the hypothalamic–pituitary–adrenal (HPA) axis. These act in concert to alter behavior in a beneficial direction. This concept explains similar symptoms for many triggering conditions, the poorly understood pathology, and the resistance to treatment.

A muscle-liver-fat signalling axis is essential for central control of adaptive adipose remodelling

Skeletal muscle has a pleiotropic role in organismal energy metabolism, for example, by storing protein as an energy source, or by excreting endocrine hormones. Muscle proteolysis is tightly controlled by the hypothalamus-pituitary-adrenal signalling axis via a glucocorticoid-driven transcriptional programme. Here we unravel the physiological significance of this catabolic process using skeletal muscle-specific glucocorticoid receptor (GR) knockout (GRmKO) mice. These mice have increased muscle mass but smaller adipose tissues. Metabolically, GRmKO mice show a drastic shift of energy utilization and storage in muscle, liver and adipose tissues. We demonstrate that the resulting depletion of plasma alanine serves as a cue to increase plasma levels of fibroblast growth factor 21 (FGF21) and activates liver-fat communication, leading to the activation of lipolytic genes in adipose tissues. We propose that this skeletal muscle-liver-fat signalling axis may serve as a target for the development of therapies against various metabolic diseases, including obesity.

Skeletal muscle proteolysis can affect organismal energy homeostasis. Here, the authors provide molecular insight into this process by showing that muscle-derived alanine acts as a signal that triggers FGF21 secretion from the liver, which then regulates lipolysis and browning of white fat tissue.

Adrenal disorders and the paediatric brain: pathophysiological considerations and clinical implications

Various neurological and psychiatric manifestations have been recorded in children with adrenal disorders. Based on literature review and on personal case-studies and case-series we focused on the pathophysiological and clinical implications of glucocorticoid-related, mineralcorticoid-related, and catecholamine-related paediatric nervous system involvement. Childhood Cushing syndrome can be associated with long-lasting cognitive deficits and abnormal behaviour, even after resolution of the hypercortisolism. Exposure to excessive replacement of exogenous glucocorticoids in the paediatric age group (e.g., during treatments for adrenal insufficiency) has been reported with neurological and magnetic resonance imaging (MRI) abnormalities (e.g., delayed myelination and brain atrophy) due to potential corticosteroid-related myelin damage in the developing brain and the possible impairment of limbic system ontogenesis. Idiopathic intracranial hypertension (IIH), a disorder of unclear pathophysiology characterised by increased cerebrospinal fluid (CSF) pressure, has been described in children with hypercortisolism, adrenal insufficiency, and hyperaldosteronism, reflecting the potential underlying involvement of the adrenal-brain axis in the regulation of CSF pressure homeostasis. Arterial hypertension caused by paediatric adenomas or tumours of the adrenal cortex or medulla has been associated with various hypertension-related neurological manifestations. The development and maturation of the central nervous system (CNS) through childhood is tightly regulated by intrinsic, paracrine, endocrine, and external modulators, and perturbations in any of these factors, including those related to adrenal hormone imbalance, could result in consequences that affect the structure and function of the paediatric brain. Animal experiments and clinical studies demonstrated that the developing (i.e., paediatric) CNS seems to be particularly vulnerable to alterations induced by adrenal disorders and/or supraphysiological doses of corticosteroids. Physicians should be aware of potential neurological manifestations in children with adrenal dysfunction to achieve better prevention and timely diagnosis and treatment of these disorders. Further studies are needed to explore the potential neurological, cognitive, and psychiatric long-term consequences of high doses of prolonged corticosteroid administration in childhood.