Nick Kruijt

Exertional heat stroke (EHS) and Malignant Hyperthermia (MH) are potentially life-threatening conditions with overlapping clinical characteristics. In this study, we compared the thermoregulatory response to exercise under increased environmental temperatures in individuals with a history of EHS (n = 15) or MH (n = 14) to healthy controls (n = 15). Groups were age- and sex-matched (31 male, 13 female, 42 ± 10 years). A 60-min exercise test was performed on a cycle ergometer at an ambient temperature of 30.3 ± 0.6°C and a relative humidity of 33.5 ± 4.7%. A stepwise incremental exercise protocol was used to reach a metabolic heat production of 6, 8 and 9 W/kg body mass. Gastrointestinal (T_gi) and skin (T_sk) temperature were monitored continuously, and partitional calorimetry was used to calculate dry (H_dry) and respiratory heat loss (H_resp). Whole-body sweat rate (WBSR) was assessed by measuring body mass. Exercise-induced increases in T_gi (1.4 ± 0.5°C) and T_sk (1.9 ± 0.8°C) were observed, but the magnitude of increase across groups was comparable (p_time*group = 0.80 and p = 0.57, respectively). H_dry was significantly lower in EHS participants (54 ± 4 W) compared to controls (65 ± 11 W, p = 0.023). No differences were observed in H_resp and WBSR. Our results suggest that individuals with MH or a history of EHS do not have an altered thermoregulatory response to exercise in the heat in a controlled setting. Further research is required to determine to what extent the complex accumulation of risk factors contributes to EHS susceptibility.

Background/Objectives: Rhabdomyolysis is a potentially life-threatening condition characterized by acute skeletal muscle breakdown. In addition to well-described external triggers, a genetic contribution is increasingly recognized. We aimed to (I) review the genetic diagnostic approach of rhabdomyolysis, (II) evaluate the clinical characteristics indicative of a genetic susceptibility with the ‘RHABDO’ acronym, and (III) assess the predictive value of the presence RHABDO features for identifying genetic variants. Methods: In this retrospective two-center study, 122 patients underwent genetic testing for rhabdomyolysis since the introduction of whole exome sequencing (WES) in 2013. The presence of RHABDO features was compared between those with (likely) pathogenic variants and those with benign or no identified variants or variants of uncertain significance. Results: The testing methods included panel-based WES (82%), Sanger sequencing (49%), and full WES (24%), of which 52 patients (43%) underwent multiple methods. A (likely) pathogenic variant was identified in 13 patients (11%), in all of whom ≥2 RHABDO features were present. The positive predictive value for ≥2 features was 14%, while the negative predictive value was 100%. Conclusions: These results highlight the relevance of WES in further elucidating the genetic basis of rhabdomyolysis and demonstrated that RHABDO is a valuable tool for selecting patients who should undergo genetic testing.

Introduction: Exertional heat stroke (EHS) is a medical emergency, occurring when the body generates more heat than it can dissipate, and frequently associated with exertional rhabdomyolysis (ERM). In the present study we aimed to (I) identify clinical features and risk factors, (II) describe current prehospital management, (III) investigate long-term outcomes including the impact on mental health, and review the guidance received during restarting activities. We hope that our approach will improve individual and organizational heat illness preparedness, and improve follow-up care. Methods: We performed a prospective online survey and retrospective medical record review among athletes and military personnel with an episode of EHS/ERM in the Netherlands between 2010 and 2020. We evaluated prehospital management, risk factors, clinical features and long-term outcomes at 6 and 12 months after the event, including mental health symptoms. Furthermore, we investigated what guidance participants received during follow-up, and assessed the patients’ perspective on these outcomes. Results: Sixty participants were included, 42 male (70%) and 18 female (30%), of which 47 presented with EHS (78%) and 13 with ERM (22%). Prehospital management was inconsistent and in the majority of participants not conducted according to available guidelines. Self-reported risk factors included not feeling well-acclimatized to environmental heat (55%) and peer pressure (28%). Self-reported long-term symptoms included muscle symptoms at rest (26%) or during exercise (28%), and neurological sequelae (11%). Validated questionnaires (CIS, HADS and SF-36) were indicative of severe fatigue (30%) or mood/anxiety disorders (11%). Moreover, 90% expressed a lack of follow-up care and that a more frequent and intensive follow-up would have been beneficial for their recovery process. Conclusion: Our findings indicate major inconsistencies in the management of patients with EHS/ERM, emphasizing the compelling need for implementing standardized protocols. Based on the results of long-term outcome measures, we recommend to counsel and evaluate every patient not only immediately after the event, but also in the long-term.

: Variants in the ryanodine receptor-1 gene (RYR1) have been associated with a wide range of neuromuscular conditions, including various congenital myopathies and malignant hyperthermia (MH). More recently, a number of RYR1 variants, mostly MH-associated, have been demonstrated to contribute to rhabdomyolysis events not directly related to anesthesia in otherwise healthy individuals. This review focuses on RYR1-related rhabdomyolysis in the context of several clinical presentations (i.e., exertional rhabdomyolysis, exertional heat illnesses and MH), and conditions involving a similar hypermetabolic state, in which RYR1 variants may be present (i.e., neuroleptic malignant syndrome and serotonin syndrome). The variety of triggers that can evoke rhabdomyolysis, on their own or in combination, as well as the number of potentially associated complications, illustrates that this is a condition relevant to several medical disciplines. External triggers include but are not limited to strenuous physical exercise, especially if unaccustomed or performed under challenging environmental conditions (e.g., high ambient temperature or humidity), alcohol/illicit drugs, prescription medication (in particular statins, other anti-lipid agents, antipsychotics and antidepressants) infection, or heat. Amongst all patients presenting with rhabdomyolysis, genetic susceptibility is present in a proportion, with RYR1 being one of the most common genetic causes. Clinical clues for a genetic susceptibility include recurrent rhabdomyolysis, creatine kinase (CK) levels above 50 times the upper limit of normal, hyperCKemia lasting for 8 weeks or longer, drug/medication doses insufficient to explain the rhabdomyolysis event, and positive family history. For the treatment or prevention of RYR1-related rhabdomyolysis, the RYR1 antagonist dantrolene can be administered, both in the acute phase or prophylactically in patients with a history of muscle cramps and/or recurrent rhabdomyolysis events. Aside from dantrolene, several other drugs are being investigated for their potential therapeutic use in RYR1-related disorders. These findings offer further therapeutic perspectives for humans, suggesting an important area for future research.

Background and purpose: Rhabdomyolysis is a medical emergency characterized by acute skeletal muscle breakdown with a sudden rise and subsequent fall of serum creatine kinase (CK) levels. Rhabdomyolysis events are provoked by exposure to external triggers, possibly in combination with an increased genetic susceptibility. We aimed to describe comprehensively the external triggers and potentially pathogenic genetic variants possibly implicated in increased rhabdomyolysis susceptibility.Methods: We performed a retrospective single‐center study, including a total of 1302 patients with an acute CK level exceeding 2000 IU/l.Results: Anoxia was the most frequently reported trigger (40%). A subset of 193 patients were clinically suspected of an underlying genetic disorder (recurrent episodes, a positive family history, very high or persistently increased CK levels). In 72 of these patients, an unequivocal genetic defect was identified. A total of 22 genes with pathogenic variants were identified, including 52 different variants. Of those, 11 genes have been previously associated with rhabdomyolysis (ACADVL, ANO5, CPT2, DMD, DYSF, FKRP, HADHA, PGM1, LPIN1, PYGM, RYR1). Eleven genes are probably implicated in increased susceptibility (including AGL, CAPN3, CNBP, DMPK, MAGT1, ACADM, SCN4A, SGCA, SGCG, SMPD1, TANGO2).Conclusion: These findings suggest that the spectrum of genetic susceptibility for rhabdomyolysis has not yet been completely clarified. With the increasing availability of next‐generation sequencing in a diagnostic setting, we expect that in more cases a genetic defect will be identified.