Is procalcitonin a marker of critical illness in heatstroke?

Serum procalcitonin levels are associated with rhabdomyolysis following exertional heatstroke: an over 10-year intensive care survey

BACKGROUND

Heatstroke has become a common emergency event in hospitals. Procalcitonin (PCT) is used as a biomarker of infection in the emergency department (ED), but its role in rhabdomyolysis (RM) following exertional heatstroke (EHS) remains unclear.

METHODS

A retrospective cohort study enrolled patients with EHS from the intensive care unit (ICU). We collected RM biomarkers, inflammation markers, critical disease scores at admission, 24 h, 48 h, and discharge, and 90-day mortality. Correlation analysis, linear regression and curve fitting were used to identify the relationship between PCT and RM.

RESULTS

A total of 162 patients were recruited and divided into RM (n=56) and non-RM (n=106) groups. PCT was positively correlated with myoglobin (Mb), acute hepatic injury, disseminated intravascular coagulation (DIC), Sequential Organ Failure Assessment (SOFA) score, and Acute Physiology and Chronic Health Evaluation II (APACHE II) score, with correlation coefficients of 0.214, 0.237, 0.285, 0.454, and 0.368, respectively (all P<0.05). Interestingly, the results of curve fitting revealed a nonlinear relationship between PCT and RM, and a two-piecewise linear regression model showed that PCT was related to RM with an odds ratio of 1.3 and a cut-off of <4.6 ng/mL. Survival analysis revealed that RM was associated with higher mortality compared to non-RM cases (P=0.0093).

CONCLUSION

High serum PCT concentrations are associated with RM after EHS in critically ill patients. Elevated PCT concentrations should be interpreted cautiously in patients with EHS in the ED.

Development and validation of a prognostic model of survival for classic heatstroke patients: a multicenter study

Classic heatstroke (CHS) is a life-threatening illness characterized by extreme hyperthermia, dysfunction of the central nervous system and multiorgan failure. Accurate predictive models are useful in the treatment decision-making process and risk stratification. This study was to develop and externally validate a prediction model of survival for hospitalized patients with CHS. In this retrospective study, we enrolled patients with CHS who were hospitalized from June 2022 to September 2022 at 3 hospitals in Southwest Sichuan (training cohort) and 1 hospital in Central Sichuan (external validation cohort). Prognostic factors were identified utilizing least absolute shrinkage and selection operator (LASSO) regression analysis and multivariate Cox regression analysis in the training cohort. A predictive model was developed based on identified prognostic factors, and a nomogram was built for visualization. The areas under the receiver operator characteristic (ROC) curves (AUCs) and the calibration curve were utilized to assess the prognostic performance of the model in both the training and external validation cohorts. The Kaplan‒Meier method was used to calculate survival rates. A total of 225 patients (median age, 74 [68-80] years) were included. Social isolation, self-care ability, comorbidities, body temperature, heart rate, Glasgow Coma Scale (GCS), procalcitonin (PCT), aspartate aminotransferase (AST) and diarrhea were found to have a significant or near-significant association with worse prognosis among hospitalized CHS patients. The AUCs of the model in the training and validation cohorts were 0.994 (95% [CI], 0.975-0.999) and 0.901 (95% [CI], 0.769-0.968), respectively. The model's prediction and actual observation demonstrated strong concordance on the calibration curve regarding 7-day survival probability. According to K‒M survival plots, there were significant differences in survival between the low-risk and high-risk groups in the training and external validation cohorts. We designed and externally validated a prognostic prediction model for CHS. This model has promising predictive performance and could be applied in clinical practice for managing patients with CHS.

Critical illness aspects of heatstroke: A hot topic

Heatstroke represents the most severe end of the heat illness spectrum, and is increasingly seen in those undergoing exercise or exertion ('exertional heatstroke') and those exposed to high ambient temperatures, for example in heatwaves ('classical heatstroke'). Both forms may be associated with significant thermal injury, leading to organ dysfunction and the need for admission to an intensive care unit. The process may be exacerbated by translocation of bacteria or endotoxin through an intestinal wall rendered more permeable by the hyperthermia. This narrative review highlights the importance of early diagnosis, rapid cooling and effective management of complications. It discusses the incidence, clinical features and treatment of heatstroke, and discusses the possible role of intestinal permeability and advances in follow-up and recovery of this condition. Optimum treatment involves an integrated input from prehospital, emergency department and critical care teams, along with follow-up by rehabilitation teams and, if appropriate, sports or clinical physiologists.

Effect of a fever in viral infections — the ‘Goldilocks’ phenomenon?

Acute infections, including those due to Coronaviridae and other viruses, often stimulate a febrile response. A mild fever appears to improve outcome; it appears to diminish viral replication by several mechanisms, including virion entry into host cells and genome transcription, and improving host defence mechanisms against the pathogen. However, a fever may also damage host cellular and tissue function and increase metabolic demands. At temperatures at the lower end of the febrile range, the benefit of the fever appears to outweigh the detrimental effects. However, at higher temperatures, the outcome worsens, suggesting that the disadvantages of fever on the host predominate. A non-infective fever is associated with a worse outcome at lower temperatures, suggesting that hyperthermia carries less benefit in the absence of infection. This review discusses the risks and benefits of a fever on the host response, focusing on the effects of a fever on viral replication and host response, and the detrimental effect on the host.

The Gastrointestinal Exertional Heat Stroke Paradigm: Pathophysiology, Assessment, Severity, Aetiology and Nutritional Countermeasures

Exertional heat stroke (EHS) is a life-threatening medical condition involving thermoregulatory failure and is the most severe condition along a continuum of heat-related illnesses. Current EHS policy guidance principally advocates a thermoregulatory management approach, despite growing recognition that gastrointestinal (GI) microbial translocation contributes to disease pathophysiology. Contemporary research has focused to understand the relevance of GI barrier integrity and strategies to maintain it during periods of exertional-heat stress. GI barrier integrity can be assessed non-invasively using a variety of in vivo techniques, including active inert mixed-weight molecular probe recovery tests and passive biomarkers indicative of GI structural integrity loss or microbial translocation. Strenuous exercise is strongly characterised to disrupt GI barrier integrity, and aspects of this response correlate with the corresponding magnitude of thermal strain. The aetiology of GI barrier integrity loss following exertional-heat stress is poorly understood, though may directly relate to localised hyperthermia, splanchnic hypoperfusion-mediated ischemic injury, and neuroendocrine-immune alterations. Nutritional countermeasures to maintain GI barrier integrity following exertional-heat stress provide a promising approach to mitigate EHS. The focus of this review is to evaluate: (1) the GI paradigm of exertional heat stroke; (2) techniques to assess GI barrier integrity; (3) typical GI barrier integrity responses to exertional-heat stress; (4) the aetiology of GI barrier integrity loss following exertional-heat stress; and (5) nutritional countermeasures to maintain GI barrier integrity in response to exertional-heat stress.

Predictors of poor prognosis in patients with heat stroke

Objective

The predictors of poor prognosis in heat stroke (HS) remain unknown. This study investigated the predictive factors of poor prognosis in patients with HS.

Methods

Data were obtained and analyzed from the health records of patients diagnosed with heat illness at Ajou university hospital between January 2008 and December 2017. Univariate and multivariate analyses were performed to identify the independent predictors of poor prognosis.

Results

Thirty-six patients (median age, 54.5 years; 33 men) were included in the study. Poor prognosis was identified in 27.8% of the study population (10 patients). The levels of S100B protein, troponin I, creatinine, alanine aminotransferase, and serum lactate were statistically significant in the univariate analysis. Multiple regression analysis revealed that poor prognosis was significantly associated with an increased S100B protein level (odds ratio, 177.37; 95% confidence interval, 2.59 to 12,143.80; P=0.016). The S100B protein cut-off level for predicting poor prognosis was 0.610 μg/L (area under the curve, 0.906; 95% confidence interval, 0.00 to 1.00), with 86% sensitivity and 86% specificity.

Conclusion

An increased S100B protein level on emergency department admission is an independent prognostic factor of poor prognosis in patients with HS. Elevation of the S100B protein level represents a potential target for specific and prompt therapies in these patients.

The efficacy of antibiotics in reducing morbidity and mortality from heatstroke - A systematic review

Severe hyperthermia, for example, classical heatstroke or exertional heatstroke from heatwaves or exercise respectively, or from drug ingestion or other non-infective pyrogens, is associated with a high mortality and morbidity, which may be chronic or permanent. Abolition of lipopolysaccharide, from gram-negative intestinal bacteria translocating into the systemic circulation via an intestinal wall rendered permeable from the hyperthermia, reduces the adverse effects, suggesting that antibiotics against the intestinal bacteria may have a similar effect. A systematic review searching Embase, MEDLINE and PubMed from the earliest date available until 2019 was conducted, according to PRISMA guidelines. Two papers were found which fit the criteria. In one, non-absorbable oral antibiotics were administered prior to the onset of heat stress, which reduced the cardiovascular dysfunction and rise in endotoxaemia, but animals succumbed at a lower temperature. In the second, non-absorbable oral antibiotics, in combination with a laxative and enema, given prior to the onset of heat stress, improved mortality; antibiotics administered after the heat stress did not, but the antibiotics used may have limited action against intestinal bacteria. Only two papers were found; both suggest an improvement in organ dysfunction or mortality after an episode of heat stress. No papers were found that investigate the sole use of antibiotics effective against intestinal bacteria given after the onset of heat stress, although biological plausibility suggest they warrant further research.

Multiple biomarkers of sepsis identified by novel time-lapse proteomics of patient serum

Serum components of sepsis patients vary with the severity of infection, the resulting inflammatory response, per individual, and even over time. Tracking these changes is crucial in properly treating sepsis. Hence, several blood-derived biomarkers have been studied for their potential in assessing sepsis severity. However, the classical approach of selecting individual biomarkers is problematic in terms of accuracy and efficiency. We therefore present a novel approach for detecting biomarkers using longitudinal proteomics data. This does not require a predetermined set of proteins and can therefore reveal previously unknown related proteins. Our approach involves examining changes over time of both protein abundance and post-translational modifications in serum, using two-dimensional gel electrophoresis (2D-PAGE). 2D-PAGE was conducted using serum from n = 20 patients, collected at five time points, starting from the onset of sepsis. Changes in protein spots were examined using 49 spots for which the signal intensity changed by at least two-fold over time. These were then screened for significant spikes or dips in intensity that occurred exclusively in patients with adverse outcome. Individual level variation was handled by a mixed effects model. Finally, for each time transition, partial correlations between spots were estimated through a Gaussian graphical model (GGM) based on the ridge penalty. Identifications of spots of interest by tandem mass spectrometry revealed that many were either known biomarkers for inflammation (complement components), or had previously been suggested as biomarkers for kidney failure (haptoglobin) or liver failure (ceruloplasmin). The latter two are common complications in severe sepsis. In the GGM, many of the tightly connected spots shared known biological functions or even belonged to the same protein; including hemoglobin chains and acute phase proteins. Altogether, these results suggest that our screening method can successfully identify biomarkers for disease states and cluster biologically related proteins using longitudinal proteomics data derived from 2D-PAGE.

Presepsin: A potential superior diagnostic biomarker for the postmortem differentiation of sepsis based on the Sepsis-3 criteria

Diagnosis of sepsis-related death by autopsy is often a complex process. Presepsin (PSEP) is typically used as a marker for diagnosing sepsis after death; however, its efficacy remains unclear. In the present study, we compared the levels of PSEP, C-reactive protein (CRP), and procalcitonin (PCT) in the postmortem serum of femoral blood to determine their efficacies as biomarkers for the postmortem differentiation of sepsis. Patients (n = 93; 48 males, 45 females with a mean age: 62.8 ± 19.2 years) who were admitted to and died in hospitals were screened for sepsis based on the sequential organ failure assessment score, and those with clinically confirmed sepsis were assessed in this study. All patients underwent autopsy within 48 h (n = 44 patients) or 48-96 h (n = 49 patients) of death. The cadavers were divided into two groups using the Sepsis-3 criteria: control group (n = 74) comprising patients without clinically diagnosed sepsis, and the group of patients who were clinically diagnosed with sepsis (n = 19). The area under the curve values (AUCs) for CRP, PCT, and PSEP levels in the sepsis group were 0.83, 0.817, and 0.977, respectively, with optimal cutoff levels of 7 mg/dL (sensitivity: 78.9%, specificity: 77.0%) for CRP, 0.07 ng/mL (sensitivity: 84.2%, specificity: 68.9%) for PCT, and 1250 pg/mL (sensitivity: 100.0%, specificity: 91.9%) for PSEP. No significant differences were noted for PSEP levels for gender, age, elapsed time after death, and the presence or absence of postmortem trauma. The present study demonstrated that compared to CRP and PCT, PSEP is a superior biomarker for the postmortem differentiation of sepsis and that a concentration >1250 pg/mL is highly likely to indicate sepsis within 96 h of death. This is the first report confirming the superiority of PSEP for diagnosing sepsis after death.

Effect of prealbumin level on mortality in heatstroke patients

This study investigated whether serum prealbumin level is associated with mortality in heatstroke patients. A retrospective study of 102 heatstroke patients admitted to the ICU in the Affiliated Changzhou No. 2 People's Hospital of Nanjing Medical University from June 2010 to November 2017 was performed they were divided into normal serum prealbumin group (n=79) and low prealbumin group (n=23) according to the difference in PA expression. The clinical data, laboratory inspection data, invasive positive pressure ventilation (IPPV), co-infection, shock and length of ICU stay during the ICU were compared between the two groups of patients. The study endpoints, deaths at admission, were recorded, and the survival curve plotted. Cox regression analysis was performed based on the clinical data of patients, and ROC curve plotted based on Cox multivariate independent prognostic indicators. There were significant differences in clinical variables PLT, ALT, AST, TBIL, ALB, TCH, LDH, TNI, BNP, creatinine, PT, APTT, FBG and D-dimer (P<0.05). The incidence of infection, shock and IPPV was significantly lower in normal serum prealbumin group of patients than those in low prealbumin group (P<0.05). There was a statistically significant difference in short-term survival rate between the groups of patients (χ²=29.101, P<0.001). Prognostic factors for heatstroke patients were IPPV, heart rate, WBC count, PLT count, ALB, PA, TBIL, LDH, CPK, Cr, PCT, PT, APTT, D-dimer, co-infection and shock at admission. Independent prognostic-related factors for heatstroke patients were IPPV, PA level, PLT level, ALB level, CPK level and PT level. When prealbumin <17.95 mg/dl was used as the death threshold for predicting at 28 days, the sensitivity was 77.8%, and the specificity was 85.7%. Significantly associated with the prognosis of heatstroke patients, prealbumin level can be used as an important predictive indicator of the disease progression and worse clinical outcomes.

Evaluation of a Novel Classification of Heat-Related Illnesses: A Multicentre Observational Study (Heat Stroke STUDY 2012)

The Japanese Association for Acute Medicine Committee recently proposed a novel classification system for the severity of heat-related illnesses. The illnesses are simply classified into three stages based on symptoms and management or treatment. Stages I, II, and III broadly correspond to heat cramp and syncope, heat exhaustion, and heat stroke, respectively. Our objective was to examine whether this novel severity classification is useful in the diagnosis by healthcare professionals of patients with severe heat-related illness and organ failure. A nationwide surveillance study of heat-related illnesses was conducted between 1 June and 30 September 2012, at emergency departments in Japan. Among the 2130 patients who attended 102 emergency departments, the severity of their heat-related illness was recorded for 1799 patients, who were included in this study. In the patients with heat cramp and syncope or heat exhaustion (but not heat stroke), the blood test data (alanine aminotransferase, creatinine, blood urea nitrogen, and platelet counts) for those classified as Stage III were significantly higher than those of patients classified as Stage I or II. There were no deaths among the patients classified as Stage I. This novel classification may avoid underestimating the severity of heat-related illness.

Impact of long distance rowing on biological health: A pilot study

OBJECTIVES

To determine the impact of long distance rowing (160km, nonstop) on standard biological parameters and to study the relation between inflammation, myocardial necrosis, lipid profile, heart rate and energy expenditure.

METHODS

Electrolytes, lipid profile, C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), procalcitonin (PCT), high-sensitive troponin T (hs-cTnT), and N-terminal pro-brain natriuretic peptide (NT-proBNP), were measured on non-fasting venous blood samples collected 8h before and after the rowing race on five healthy competitors. Heart rate and energy expenditure were measured using sporting self-measurement devices.

RESULTS

After 16.5h of race, significant increases in median CRP (+25.2mg/l; p=0.04), IL-6 (+1.85pg/ml; p=0.04), TNF-α (+1.2pg/ml; p=0.04) and NT-proBNP levels (+88.8pg/ml; p=0.04) were observed, and a close to significant elevation for hs-cTnT(+6ng/l; p=0.06) and PCT (+0.14μg/l; p=0.07). On the other hand, significant decrease in median total cholesterol (-0.5mmol/l; p=0.04), triglycerides (-0.7mmol/l; p=0.04) were observed. Furthermore, significant correlations between the maximal heart rate reached during the race and CRP (r=0.90; p=0.03), IL-6 (r=0.90; p=0.03), and NT-proBNP (r=0.90; p=0.03) were observed, whereas no such associations were retrieved with median heart rate, the percentage of time passed over 70% of maximal heart rate or energy expenditure during the race. There was no association between PCT, NT-proBNP, hs-cTnT, inflammatory biomarkers, lipid profile or heart rate parameters.

CONCLUSIONS

Long distance rowing induces inflammation and myocardial strain related to the maximal effort generated during the race, but has a favourable effect on lipid profile.

Outcome and risk factors associated with extent of central nervous system injury due to exertional heat stroke

To explore the relationship between the extent of central nervous system (CNS) injury and patient outcomes meanwhile research the potential risk factors associated with neurologic sequelae. In this retrospective cohort study, we analyzed data from 117 consecutive patients (86 survivors, 31 nonsurvivors) with exertional heat stroke (EHS) who had been admitted to intensive care unit (ICU) at 48 Chinese hospitals between April 2003 and July 2015. Extent of CNS injury was dichotomized according to Glasgow coma scale (GCS) score (severe 3-8, not severe 9-15). We then assessed differences in hospital mortality based on the extent of CNS injury by comparing 90-day survival time between the patient groups. Exploring the risk factors of neurologic sequelae. The primary outcomewas the 90-day survival ratewhich differed between the 2 groups (P = .023). The incidence of neurologic sequelae was 24.4%. For its risk factors, duration of recurrent hyperthermia (OR = 1.73, 95% CI: 1.20-2.49, P = .003), duration of CNS injury (OR = 1.39, 95% CI: 1.04-1.85, P = .025), and low GCS in the first 24 hours after admission (OR = 2.39, 95% CI: 1.11-5.15, P = .025) were selected by multivariable logistic regression. Cooling effect was eliminated as a factor (OR = 2641.27, 95% CI 0.40-1.73_107, P = .079). Significant differences in 90-day survival ratewere observed based on the extent of CNS injury in patients with EHS, and incidence was 24.4% for neurologic sequelae. Duration of recurrent hyperthermia, duration of CNS injury, and low GCS score in the first 24 hours following admission may be independent risk factors of neurologic sequelae. Cooling effect should be validated in the further studies.

The pathophysiological basis and consequences of fever

There are numerous causes of a raised core temperature. A fever occurring in sepsis may be associated with a survival benefit. However, this is not the case for non-infective triggers. Where heat generation exceeds heat loss and the core temperature rises above that set by the hypothalamus, a combination of cellular, local, organ-specific, and systemic effects occurs and puts the individual at risk of both short-term and long-term dysfunction which, if severe or sustained, may lead to death. This narrative review is part of a series that will outline the pathophysiology of pyrogenic and non-pyrogenic fever, concentrating primarily on the pathophysiology of non-septic causes.

Prognostic value of PCT, copeptin, MR-proADM, MR-proANP and CT-proET-1 for severe acute dyspnea in the emergency department: the BIODINER study

CONTEXT

Acute dyspnea is a frequent complaint in patients attending the emergency department (ED).

OBJECTIVE

To evaluate the accuracy of PCT, MR-proANP, MR-proADM, copeptin and CT-proET1 for the risk-stratification of severe acute dyspnea patients presenting to the ED.

METHODS

Multicenter prospective study in adult patients with a chief complaint of acute dyspnea. Pro-hormone type biomarkers concentrations were measured on arrival. Combined primary endpoint was a poor outcome.

RESULTS

Three hundred and ninety-four patients were included, 137 (35%) met the primary endpoint. MR-proADM was the only biomarker associated with the primary endpoint (odds ratio 1.43 [95%CI: 1.13-1.82], p = 0.003) as were the presence of paradoxical abdominal breathing (odds ratio 2.48 [95%CI: 1.31-4.68]) or cyanosis (odds ratio 3.18 [1.46-6.89]) Conclusions: In patients with severe acute dyspnea in the ED, pro-hormone type biomarkers measurements have a low added value to clinical signs for the prediction of poor outcome.

Hospitalized dogs recovery from naturally occurring heatstroke; does serum heat shock protein 72 can provide prognostic biomarker?

Heatstroke is a serious illness in dogs characterized by core temperatures above 41°C with central nervous system dysfunction. Experimental heatstroke models have tried to correlate biomarker levels with the severity of the syndrome. Serum heat shock protein (eHSP70) levels were recently evaluated as a biomarker of heat tolerance and acclimation, their role as a marker of heatstroke is inconclusive. Here, we monitored eHSP70 levels in correlation with systemic biomarkers in 30 naturally occurring canine heatstroke cases. Thirty dogs diagnosed with environmental (33%) or exertional (66%) heatstroke admitted to hospital (0-14 h post-injury) were tested for biomarkers of organ damage and coagulation parameters. eHSP70 levels were measured upon admission and 4, 12, and 24 h later (T1, T2, and T3, respectively). No differences were found between exertional and environmental heatstroke cases. The eHSP profile demonstrated an inverted bell shape, with the lowest levels at the 12 h time point. A positive correlation between eHSP70, lactate, and aPPT was also noted at T2 in all the dogs in the study. Twenty-four h after presentation, eHSP70 levels returned to those measured upon admission, this change was only significant in the survivors. The obtained results suggest that eHSP72 level profile may be predictive of survival.

Update on procalcitonin measurements

Procalcitonin (PCT) is used as a biomarker for the diagnosis of sepsis, severe sepsis and septic shock. At the same time, PCT has also been used to guide antibiotic therapy. This review outlines the main indications for PCT measurement and points out possible pitfalls. The classic indications for PCT measurement are: (i) confirmation or exclusion of diagnosis of sepsis, severe sepsis, or septic shock, (ii) severity assessment and follow up of systemic inflammation mainly induced by microbial infection, and (iii) individual, patient adapted guide of antibiotic therapy and focus treatment. Using serially monitored PCT levels, the duration and need of antibiotic therapy can be better adapted to the individual requirements of the patient. This individualized approach has been evaluated in various studies, and it is recommended to be a part of an antibiotic stewardship program.

Early elevated HMGB1 level predicting the outcome in exertional heatstroke

BACKGROUND

Heatstroke is generally considered as a syndrome of hyperthermia associated with systemic inflammation leading to multiorgan dysfunction. High mobility group box-1 protein (HMGB1) has recently been identified as a late mediator of systemic inflammation inducing multiorgan dysfunction. Elevation of plasma HMGB1 in heatstroke has been observed in animals, but there is no data available about its changes in heatstroke patients. The objectives of this study are to observe the time course of plasma HMGB1 changes and assess its prognostic value in patients with exertional heatstroke.

METHODS

Blood samples were taken from the patients with exertional heatstroke. Plasma HMGB1 level was detected by the enzyme-linked immunosorbent assay. C-reactive protein level was measured using a fully automated IMMAGE Immunochemistry System. Secreted HMGB1 in the culture supernatant of peripheral blood monocyte was assessed by immunoblotting. Acute Physiology and Chronic Health Evaluation II score was evaluated within 24 hours of admission.

RESULTS

HMGB1 released into circulation at early stage, with peak levels occurring within 6 hours to 13 hours postheatstroke. Plasma HMGB1 levels remained markedly elevated in the following 6 days postheatstroke when compared with healthy volunteers (p<0.005). Positive correlation (r=0.798, p<0.001) was found between Acute Physiology and Chronic Health Evaluation II score and HMGB1 level at admission. HMGB1 levels at admission between survivors and nonsurvivors were significantly different (p<0.001). Receiver operating curve analysis showed that at a level of 47 ng/mL, HMGB1 level at admission indicated lethality with 77.4% sensitivity and 84.2% specificity.

CONCLUSIONS

HMGB1 level at admission is an indicator of the severity of illness and a useful mortality predictor in exertional heatstroke.

Neuroleptic malignant syndrome: mechanisms, interactions, and causality

This review focuses on new data from recent publications concerning how compounding interactions between different thermoregulatory pathways influence the development of hyperthermia and/or neuroleptic malignant syndrome (NMS), and the fundamental issue of the presumed causal role of antipsychotic drugs. The formal criteria for substantiating cause-effect relationships in medical science, established by Hill, are applied to NMS and, for comparison, also to malignant hyperthermia and serotonin toxicity. The risk of morbidities related to hyperthermia is reviewed from human and experimental data: temperatures in excess of 39.5°C cause physiological and cellular dysfunction and high mortality. The most temperature-sensitive elements of neural cells are mitochondrial and plasma membranes, in which irreversible changes occur around 40°C. Temperatures of up to 39°C are "normal" in mammals, so, the term hyperthermia should be reserved for temperatures of 39.5°C or greater. The implicitly accepted presumption that NMS is a hypermetabolic and hyperthermic syndrome is questionable and does not explain the extensive morbidity in the majority of cases, where the temperature is less than 39°C. The thermoregulatory effects of dopamine and acetylcholine are outlined, especially because they are probably the main pathways by which neuroleptic drugs might affect thermoregulation. It is notable that even potent antagonism of these mechanisms rarely causes temperature elevation and that multiple mechanisms, including the acute phase response, stress-induced hyperthermia, drugs effects, etc., involving compounding interactions, are required to precipitate hyperthermia. The application of the Hill criteria clearly supports causality for drugs inducing both MH and ST but do not support causality for NMS.