Thermoregulatory dysfunction in neuroleptic malignant syndrome

Neural cell-types and circuits linking thermoregulation and social behavior

Understanding how social and affective behavioral states are controlled by neural circuits is a fundamental challenge in neurobiology. Despite increasing understanding of central circuits governing prosocial and agonistic interactions, how bodily autonomic processes regulate these behaviors is less resolved. Thermoregulation is vital for maintaining homeostasis, but also associated with cognitive, physical, affective, and behavioral states. Here, we posit that adjusting body temperature may be integral to the appropriate expression of social behavior and argue that understanding neural links between behavior and thermoregulation is timely. First, changes in behavioral states-including social interaction-often accompany changes in body temperature. Second, recent work has uncovered neural populations controlling both thermoregulatory and social behavioral pathways. We identify additional neural populations that, in separate studies, control social behavior and thermoregulation, and highlight their relevance to human and animal studies. Third, dysregulation of body temperature is linked to human neuropsychiatric disorders. Although body temperature is a "hidden state" in many neurobiological studies, it likely plays an underappreciated role in regulating social and affective states.

Bench-to-bedside review: mechanisms and management of hyperthermia due to toxicity

Body temperature can be severely disturbed by drugs capable of altering the balance between heat production and dissipation. If not treated aggressively, these events may become rapidly fatal. Several toxins can induce such non-infection-based temperature disturbances through different underlying mechanisms. The drugs involved in the eruption of these syndromes include sympathomimetics and monoamine oxidase inhibitors, antidopaminergic agents, anticholinergic compounds, serotonergic agents, medicaments with the capability of uncoupling oxidative phosphorylation, inhalation anesthetics, and unspecific agents causing drug fever. Besides centrally disturbed regulation disorders, hyperthermia often results as a consequence of intense skeletal muscle hypermetabolic reaction. This leads mostly to rapidly evolving muscle rigidity, extensive rhabdomyolysis, electrolyte disorders, and renal failure and may be fatal. The goal of treatment is to reduce body core temperature with both symptomatic supportive care, including active cooling, and specific treatment options.

“Thermoregulation-dependent component” in pathophysiology of motor disorders in Parkinson's disease?

Parkinson's disease (PD) is a neurodegenerative disorder characterised by motor symptoms (resting tremor, brady- or akinesia and muscle rigidity), and also by postural problems gait disorder and fatigue as well as behavioural and autonomic symptoms, including thermoregulatory impairment. These symptoms are strikingly similar with some motor phenomena, evoked by the whole body cooling, though the primary cause of PD and cold-induced symptoms are apparently different. The review is focused on the hypothesis that thermoregulatory mechanisms are involved in pathophysiology of motor disorders in PD. The comparative analysis provides some examples of analogy between PD and the state of cooling in respect with tremor, muscle hypertonus, postural reactions and impairment of gross and fine muscle performance. This analogy cannot be considered as specific, because in some normal conditions the motor system utilises identical strategy to compensate for motor deterioration, e.g. at fatigue and ageing. However, such motor phenomena, as neuroleptic malignant syndrome and paired discharges of motor units indicate that the "thermoregulation-dependent component" exists in the pathophysiology of PD. Data on the influence of the whole body cooling and heating on muscle performance, rigidity and tremor in PD patients also provide evidence for the involvement of thermoregulatory mechanisms in PD.

Neuroleptic malignant syndrome: risk factors, pathophysiology, and treatment

Neuroleptic malignant syndrome (NMS) is associated with the administration of antipsychotic agents and other drugs such as l-dopa, antidepressants, and antihistaminic agents. Unexpected changes in mental status, new-onset catatonia, episodic tachycardia, tachypnea, hypertension, dysarthria, dysphagia, diaphoresis, sialorrhea, incontinence, low-grade temperature elevations, and rigidity should arouse suspicion. Several lines of evidence provide support for the involvement of dopamine. Most of the drugs implicated in NMS are D2 dopamine receptor antagonists. Central noradrenergic activity is also possibly related to the disorder, as sympathetic hyperactivity is associated with the active phase of NMS. Currently, the definitive role of GABA deficiency in NMS is yet to be established. Differential diagnosis should include malignant hyperthermia, lethal catatonia, lithium toxicity, serotonin syndrome, and heat stroke. A high degree of suspicion and the discontinuation of antipsychotic agents even if the diagnosis is not established are essential for the safety of the patient. Treatment of NMS should be individualized and be based empirically on the character, duration, and severity of the clinical signs and symptoms noted. The initial step in the treatment of NMS is the removal of the offending agent. Full-blown NMS is a serious condition and requires immediate supportive, nutritive, and electrolyte therapies. The administration of drugs that can improve NMS, such as IV dantrolene and/or oral bromocriptine, may also be taken into consideration, based on the severity and nature of the NMS.

Drug-induced hyperthermia and muscle rigidity: a practical approach

Body thermoregulation can be violently offset by drugs capable of altering the balance between heat production and dissipation. Such events may rapidly become fatal. The drugs that are involved in the eruption of such syndromes include inhalation anaesthetics, sympathomimetic agents, serotonin antagonists, antipsychotic agents and compounds that exhibit anticholinergic properties. The resultant hyperthermia is frequently accompanied by an intense skeletal muscle hypermetabolic reaction that leads to rapidly evolving rigidity, extensive rhabdomyolysis and hyperkalemia. The differential diagnosis should, however, rule out non-drug-induced causes, such as lethal catatonia, central nervous system infection or tetanus, strychnine poisoning, thyrotoxic storm and pheochromocytoma. Prompt life-saving procedures include aggressive body temperature reduction. Patients with a suspected drug (or non-drug) hypermetabolic reaction should be admitted into an intensive care area for close monitoring and system-oriented supportive treatment. We present six conditions, in decreasing order of gravity and potential lethality, in which hyperthermia plays an essential role, and suggest a clinical approach in such conditions.

Withdrawal of levodopa and other risk factors for malignant syndrome in Parkinson's disease

A symptom complex identical to neuroleptic malignant syndrome (MS) is known to develop in patients with idiopathic Parkinson's disease (PD) or other forms of parkinsonism on long-term treatment with anti-parkinsonian drugs. In order to clarify the risk factors for parkinsonian MS, the authors retrospectively reviewed charts of consecutive inpatients with PD in the neurological departments at the three hospitals and found 16 episodes of parkinsonian MS in 14 patients. A survey of health status preceding MS disclosed that deterioration of parkinsonian symptoms alone may induce MS, while association of major risk factors, i.e. rapid discontinuation of anti-parkinsonian drugs, dehydration or infection may precipitate or exacerbate MS. Cerebral vascular disorders, mechanical brain injury or physiological stress could be other risk factors leading to MS.

Hyperpyrexia in the emergency department

The differential diagnosis of the hyperpyrexic patient in the emergency department is extensive. It includes sepsis, heat illness including heat stroke, neuroleptic malignant syndrome, malignant hyperthermia, serotonin syndrome and thyroid storm. Each of these possible diagnoses has distinguishing features that may help to differentiate one from another. However, establishing the correct diagnosis is a challenge in the setting of the obtunded emergency patient who gives no history and where there may be limited access to any past medical or drug history. This paper presents such a case and reviews the features of the differential diagnoses and management of the hyperpyrexic patient.

Sympathoadrenal hyperactivity and the etiology of neuroleptic malignant syndrome

OBJECTIVE

The author's goal was to develop a pathophysiological model for neuroleptic malignant syndrome with greater explanatory power than the alternative hypotheses of hypothalamic dopamine antagonism (elevated set point) and direct myotoxicity (malignant hyperthermia variant).

METHOD

Published clinical findings on neuroleptic malignant syndrome were integrated with data from human and animal studies of muscle physiology, thermoregulation, and autonomic nervous system function.

RESULTS

The data show that the sympathetic nervous system's latent capacity for autonomous activity is expressed when tonic inhibitory inputs from higher central nervous system centers are disrupted. These tonic inhibitory inputs are relayed to preganglionic sympathetic neurons by way of dopaminergic hypothalamospinal tracts. The sympathetic nervous system mediates hypothalamic coordination of thermoregulatory activity and is a primary regulator of muscle tone and thermogenesis, augmenting both of these when stimulated. In addition, the sympathetic nervous system modulates all of the other end-organs that function abnormally in neuroleptic malignant syndrome.

CONCLUSIONS

There is substantial evidence to support the hypothesis that dysregulated sympathetic nervous system hyperactivity is responsible for most, if not all, features of neuroleptic malignant syndrome. A predisposition to more extreme sympathetic nervous system activation and/or dysfunction in response to emotional or psychological stress may constitute a trait vulnerability for neuroleptic malignant syndrome, which, when coupled with state variables such as acute psychic distress or dopamine receptor antagonism, produces the clinical syndrome of neuroleptic malignant syndrome. This hypothesis provides a more comprehensive explanation for existing clinical data than do the current alternatives.

Diaphoresis and dehydration during neuroleptic malignant syndrome: preliminary findings

Serum osmolality and its relationship to diaphoresis and polydipsic behavior were examined in a series of 38 episodes of neuroleptic malignant syndrome (NMS) in 29 patients. Clinical variables were associated with significantly higher serum osmolality, and diaphoresis tended to emerge earlier than polydipsia in the course of NMS. The findings of this study are consistent with the hypothesis that, at least in some NMS patients, diaphoresis leads to dehydration followed by physiologically appropriate thirst and increased oral water intake. It appears that intravenous hydration is often necessary to correct the significant free water deficit that can occur during the course of NMS.