Exertional Rhabdomyolysis and Malignant Hyperthermia in a Patient with Ryanodine Receptor Type 1 Gene, L-type Calcium Channel α-1 Subunit Gene, and Calsequestrin-1 Gene Polymorphisms

Abstract

THE relationship between hypermetabolic exertional stress injuries and malignant hyperthermia (MH) has been a topic of debate for almost 30 yr. Central to this debate is the idea that some MH susceptible (MHS) patients may develop awake nonanesthesia-related manifestations similar to that seen in porcine stress syndrome.1–7Although a link has never been established by controlled clinical studies, individual case reports and a small number of clinical series support an association between unexpected exertional rhabdomyolysis (ER) and MH susceptibility,8two syndromes characterized by abnormal intracellular skeletal muscle calcium regulation.9,10An individual is identified as MHS if he or she has a well-documented clinical episode consistent with MH during exposure to any of the known anesthetic triggering agents, or if he or she has undergone a skeletal muscle biopsy with a positive diagnostic contracture test. However, none of the published reports of patients who presented first with ER and who were subsequently identified as MHS by a positive contracture test ever developed documented clinical MH episodes involving anesthesia.11–16We present a case that is compelling for two reasons. First, it is the only documented case of an individual who presented first with ER, followed by a clinical MH episode during anesthesia, and then by a positive contracture test. Second, genetic analysis revealed the presence of variants in the ryanodine receptor type 1 gene (RYR1 ), the L-type calcium channel α-1 subunit gene (CACNA1S ), and the calsequestrin-1 gene (CASQ1 ). This report provides clinical evidence for an association between ER and MH and discusses the possible role for synergistic action among rare variants in the genes encoding proteins crucial to skeletal muscle calcium regulation.A physically fit, muscular, 30-yr-old, 93-kg African American presented to the emergency department with intense bilateral calf pain after a 2.5-mile walk. He had a history of bilateral patella syndrome and was diagnosed with an acute exacerbation. Rest, diazepam, and oxycodone/acetaminophen were prescribed. His medical history was significant for hypertension and hyperlipidemia treated with hydrochlorothiazide (25 mg daily) and simvastatin (20 mg daily), respectively. Simvastatin was prescribed approximately 1 month before this episode, and he provided no history consistent with statin-induced myopathy or episodes of ER. The calf pain increased in intensity over the ensuing week after which he was re-presented to the emergency department and was diagnosed with ER (creatine kinase [CK] > 10,000 U) and bilateral calf compartment syndrome, requiring surgical fasciotomies. Preoperative toxicology screen test results were negative for methadone, amphetamines, barbiturates, cannabinoids, cocaine, phencyclidine, benzodiazepines, and opiates, despite having been prescribed diazepam and oxy-codone. There were no other medications identified in this patient, which are associated with rhabdomyolysis. Complete blood count, electrolytes, and urine myoglobin were normal. Procedures to rule out lower extremity vascular lesions were not performed. Before surgery, he denied a personal or family history of MH, use of dietary supplements, and heat intolerance. However, he did report occasional muscle cramping.Bilateral four-compartment lower extremity (calves) fasciotomies were performed with general endotracheal anesthesia. General anesthesia was induced with intravenous midazolam (4 mg), fentanyl (200 μg), lidocaine (50 mg), propofol (180 mg), rocuronium (10 mg) and succinycholine (100 mg), followed by the placement of an 8.0 endotracheal tube. Anesthesia was maintained with intravenous fentanyl (350 μg total dose), and inhaled nitrous oxide (50%), oxygen (50%), and sevoflurane (2.4%). At the completion of surgery, no neuromuscular reversal agents were administered, inhalational anesthetics were discontinued, the oropharynx was suctioned, and the patient was extubated and recovered without complication. During the procedure, the heart rate ranged from 98 to 105 beats/min, blood pressure ranged from 110 to 130 mmHg over 60 to 80 mmHg, and end-tidal carbon dioxide ranged from 30 to 40 mmHg with pressure-controlled minute ventilation ranging from 6.0 to 6.8 l/min. The esophageal temperature ranged from 36.5° to 37.1°C. Because the patient had an allergy to penicillin, clindamycin (600 mg, intravenously) administration was begun before incision and completed within 45 min.One day later, he returned to the operating room for a 30-min irrigation and debridement of his fasciotomy wounds. His serum CK had decreased from 10,609 U on the day of admission to 3,842 U. Before the second surgery, he was afebrile (37°C), tachycardic (110 beats/min), hypertensive (187/117 mmHg), and complained of intense calf pain. Although the tachycardia and hypertension might have been signs of other metabolic causes, it was thought to be secondary to pain, as the surgeons requested conservative postoperative pain management out of fear that high opioid or epidural analgesia might mask a worsening compartment syndrome. Midazolam (2 mg, intravenously) and fentanyl (100 μg, intravenously) helped to reduce the pain, but had no immediate effect on the tachycardia and hypertension. In the operating room, he was preoxygenated, and general anesthesia was induced with intravenous propofol (200 mg). Isoflurane (1%) was administered after placement of a #4 Laryngeal Mask Airway ™ (The Laryngeal Mask Company Limited, Le Rocher, Victoria, Mahe, Seychelles). Spontaneous ventilation was confirmed via breath sounds and capnography, and he was transferred from his hospital bed to the operating table while anesthesia was maintained with isoflurane and 100% oxygen. No depolarizing or nondepolarizing neuromuscular blocking agents were administered.Total body rigidity developed of sufficient severity that the patient's arms could not be abducted and placed on arm boards. The surgeon likewise remarked at how stiff the patient's legs had become. The capnography reading was then lost as the patient developed severe trismus, occluding the Laryngeal Mask Airway ™. Heart rate increased to 128 beats/min. Inadequate anesthesia was suspected, so the isoflurane was increased to 2% and another 150 μg of intravenous fentanyl was administered. Forceful manual ventilation was begun via the partially occluded Laryngeal Mask Airway ™ and end-tidal carbon dioxide reappeared on the capnograph. The nasal temperature probe registered 38.5°C. There were no signs of an infectious etiology, and the patient was not being externally warmed. Spontaneous ventilation resumed at 20–22 breaths/min, despite total doses of 2 mg midazolam, 250 μg fentanyl, 200 mg propofol, and 2% isoflurane. End-tidal carbon dioxide increased as high as 70 mmHg, but it was unclear whether this was due to hypoventilation through a partially occluded Laryngeal Mask Airway ™ or the result of a hypermetabolic phenomenon.Isoflurane was discontinued, 100% oxygen was delivered at a rate of 10 l/min, and total intravenous anesthesia was started with 150 μg · kg−1· min−1propofol. The rigidity resolved and end-tidal carbon dioxide decreased to 55 mmHg with a spontaneous respiratory rate of 12–15 breaths/min. Nasal temperature decreased from 38.5° to 38.1°C. Tachycardia and hypertension resolved with intravenous metoprolol (5 mg). Although a diagnosis of MH was considered, the presentation was unclear, especially because the signs of MH appeared to resolve with the administration of a propofol infusion and metoprolol. Thus, arterial blood gases were not obtained, nor was dantrolene administered at this point. However, the plan was to closely observe the patient for any suspicious signs of MH. The case was concluded within 20 min without further complication, and the patient was extubated and transferred to the postanesthesia care unit for close observation.Initial oral temperature in the postanesthesia care unit was 37.7°C. Although pain was well controlled, tachycardia (110) and hypertension (170/100) returned and did not respond to labetalol (30 mg intravenously over 30 min). Within 45 min of entering the postanesthesia care unit, oral temperature had risen to 39.4°C. A radial arterial catheter was placed, and arterial blood gases and CK were ordered. The arterial blood gases were 7.404/44.3/118/3/27.7/99% and CK was 4,197 U. Serum potassium had increased to 4.8 mm, compared with 4.0 mm on the morning before surgery. The patient was transferred to the surgical intensive care unit and given an intravenous bolus of dantrolene (240 mg) approximately 1.5 h after signs of MH first appeared during anesthesia induction. Two hours after the dantrolene loading dose, rectal core temperature was still 39.7°C, and the serum potassium was 5.4 mm. Consistent with the recommended management of MH, a second dose of intravenous dantrolene (1 mg/kg) was given because the fever had not resolved. During the next several hours, serial CKs showed a decline, and by the next morning, rectal core temperature was 37.1°C. Urine myoglobin was negative. Thyroid panel and metanephrines were normal, and no further workup was ordered for thyroid disease and pheochromocytoma. Retrospectively, the MH clinical grading scale was used, and a score of 53 was calculated for a rank of 6 and qualitative likelihood of “almost certain.”17Six months later, the patient underwent a left vastus lateralis muscle biopsy for MH testing with a caffeine halothane contracture test (CHCT). The CHCT result was positive for 3% halothane (0.7, 0.9, and 0.6 g of tension in three separate muscle strips), but negative for caffeine.18Although these results are considered MHS by North American MH standards, the negative response to caffeine constitutes an MH equivocal diagnosis by European standards.19Despite the discontinuation of statin therapy and reporting no sequelae, the patient's baseline CK at the day of the biopsy was 417 U (normal, 50–200 U). Standard muscle histology testing showed mild denervation atrophy. As a part of an ER evaluation, an Exercise Intolerance Mutation Panel test (Robert Guthrie Biochemical and Molecular Genetics Laboratory, Buffalo, NY) was performed. This DNA blood test screens for the most common mutations in the CPT2 (S113 l, Q413fs, P50H, G549D), PYGM (R50X, G205S) and AMPD1 (Q12X, P48 l) genes, which code for enzyme deficiencies in carnitine palmitoyltransferase II, myophosphorylase, and myoadenylate deaminase, respectively.20In addition, a Myoglobinuria Evaluation test (Athena Diagnostics, Inc., Worcester, MA) was performed on frozen muscle obtained at the time of the biopsy. Specifically, this evaluation tests for enzymatic deficiencies in phosphorylase A, phosphorylase b kinase, myoadenylate deaminase, phosphoglycerate kinase, phosphoglycerate mutase, lactate dehydrogenase, carnitine palmitoyltransferase II, and glycogen.20Both the Exercise Intolerance Mutation Panel and Myoglobinuria Evaluation test results were negative.With approval of the Institutional Review Board of the Uniformed Services University of the Health Sciences (Bethesda, Maryland), written informed consent was obtained from the patient to sequence the entire coding regions for the RYR1 , CACNA1S , and CASQ1 genes. Sequencing was performed using complementary DNA transcribed from messenger RNA extracted from muscle to capture intronic mutations that have splicing effects. Complete sequencing of RYR1 and CASQ1 was performed as described by Sambuughin et al. 21In brief, the complementary DNA was synthesized using messenger RNA extracted from muscle and amplified in 2 and 25 overlapping fragments for CASQ1 and RYR1 , respectively. Primers used for this purpose were designed using Primer 3 software.∥The sequence variants were determined by direct sequencing of polymerase chain reaction fragments using an ABI 3100 DNA analyzer (Applied Biosystems, Foster City, CA). Direct sequencing of the polymerase chain reaction product was performed in one or both directions depending on sequencing results.Gene sequencing revealed RYR1 variant Ser1342Gly in exon 28, CACNA1S variant Leu1800Ser in exon 44, and CASQ1 variant His66Arg in exon 1. All polymorphisms were heterozygous. No splice variants were found. Genetic testing was not performed in the patient's parents or close relations. Both RYR1 and CACNA1S variants found in this patient are reported in the public database (Single Nucleotide Polymorphism, National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD). The Leu1800Ser CACNA1S variant is most common in African Americans (frequency range, 0.46–0.60), followed by Asians (0.15) and Caucasian (0.08). The Ser1342Gly RYR1 variant, however, is rare and identified only in the African American population with a frequency of 0.04. The frequency of the CASQ1 His66Arg variant identified in this study was estimated in healthy controls representing three ethnic groups: African Americans (N = 70), Caucasian Americans (N = 80, including 50 MH negative by CHCT), and Asians (Chinese and Mongolians, collected from mainland Asians with no intervening generation of ancestors resident in North America, N = 50). Ethnicity for controls was determined by self-report (mixed heritage unknown). There was no bias in identifying the population of the samples tested. All controls had been collected for previous similar studies21,22and were made available for this study without personal identification. With approval of the Institutional Review Board of the Uniformed Services University of the Health Sciences, written informed consent was obtained from controls to use their tissue for any scientific purpose involving any approved future project. Caucasian Americans and Asian controls tested negative for the CASQ1 His66Arg variant. Three African American controls contained the variant, providing an estimate for allele frequency at 0.02 among this population.Rhabdomyolysis is a potentially fatal clinical syndrome caused by the dissolution and disintegration of striated muscle. The diagnosis is based on a complaint of muscle pain or weakness in the presence of elevated serum CK. Severe or untreated cases may result in life-threatening hyperkalemia, myoglobinuria, renal failure, and multiorgan system failure.9The etiology of rhabdomyolysis is diverse, and its actual incidence is unknown.23Rhabdomyolysis is under-reported at approximately 26,000 cases in the United States each year, accounting for 5–7% of all cases of acute renal failure.9The true incidence is likely much higher.ER is a frequent complication of exertional heat illness, but can occur in the absence of high environmental or core body temperatures. ER occurs in response to strenuous eccentric exercise when mechanical or metabolic stress damages skeletal muscle.23Although the diagnostic criteria for ER are somewhat controversial, clinical practice guidelines typically define rhabdomyolysis as a serum CK greater than or equal to five times the upper limit of normal.23Under extreme physical and environmental conditions anyone may develop ER.9However, some individuals to be than a metabolic myopathy or genetic diagnosis for ER is and the of this a on the the is to any of the MH is a myopathy characterized by a hypermetabolic syndrome during and after anesthesia that is as a RYR1 and CACNA1S , the only genes identified to be associated with proteins to the calcium in the of skeletal muscle. MH are to skeletal muscle calcium by inhalational anesthetics or of an MH can skeletal muscle hyperkalemia, elevated multiorgan system failure, and MH is a syndrome characterized by and individuals not develop clinical MH episodes with exposure to anesthetic triggering agents, nor is the and clinical of the syndrome Because previous anesthesia with MH triggering agents not future any signs of trismus, and when agents are anesthesia to tests of ER and MH are hypermetabolic that a high for and mechanical stress of and an in intracellular the and severe muscle and occurs in have the that ER and MH are syndromes by et al. showed that calcium was increased in muscle from patients with ER. a known of calcium from the and the only for MH, decreased calcium in ER patients and clinical testing for MH the in contracture test test used in and CHCT test used in North has been used to the MHS of ER Although the idea that or awake episodes of MH similar to that seen in porcine stress syndrome was 30 first series of patient that described an association between ER and positive was reported in have been cases reported of individuals with ER who have positive CHCT or some of have RYR1 most on this topic is by et al. which 10 of ER patients without personal or family of MH were and 3 of the 10 positive patients were found to have known RYR1 However, no episodes of MH ever followed the and of ER. Although these reported ER cases the criteria for MH none the clinical this are several in using or CHCT in the evaluation of ER. the of the CHCT is a rate of the CHCT some patients as MHS and some CHCT and the were for clinical MH during anesthesia and not for clinical ER. Thus, to an ER patient without a clinical history of MH as MHS because the criteria or is ER patients may be as MHS by contracture but this not that a relationship is European and North American CHCT in that a positive muscle contracture response to halothane or caffeine is considered MHS in North America, but MH equivocal in support for an association between exertional heat and MH is by in with a MH gene developed muscle and in response to elevated environmental these did not develop rhabdomyolysis when muscle was to of eccentric when core temperature was maintained at lower during these a of only one RYR1 of over RYR1 variants that have been the in genetic only of MHS patients an RYR1 than for CACNA1S it is that are gene mutations that MH CASQ1 has been identified as another possible gene a in the of skeletal muscle. as both a and a of ryanodine receptor calcium developed and in response to 2% halothane or heat stress these developed elevated core and severe which was by previous dantrolene is unclear the genetic in the RYR1 CACNA1S and CASQ1 in this because occur at of and in African American The RYR1 and CASQ1 variants are rare polymorphisms identified only in African American CASQ1 His66Arg is a variant and His at of the is of skeletal and muscle is to that the Ser1342Gly RYR1 variant was reported in association with MHS in a Caucasian in another MHS patient of University of written personal to patient, both these patients other gene have found the Ser1342Gly variant in with other variants in other African American ER patients who are CHCT presence of rare RYR1 variants or of RYR1 and CACNA1S variants is reported in a number of MHS with no further of the the case of the presence of two polymorphisms was associated with is possible that the presence of rare gene variants encoding in proteins for calcium to ER and MH in of these genetic is to whether are is that the genetic used not or any one of which or in may to topic of is the role that statin therapy may have in ER or MH. can be to in intracellular and are among the most for for the statin agents to an estimated in the United States by the of may for as as cases of rhabdomyolysis in the United States as CK than 10 times the upper limit of with muscle pain, or has an incidence of it has been that exercise in with greater CK than by exercise that can skeletal muscle of statin therapy can be of statin therapy not At of patients with severe statin myopathy have for greater than 6 and some patients have for greater than muscle from individuals that of the system and but Thus, CK not from these the of is but may be to of small proteins in that may to the of to be to or muscle of muscle that to the of as well as ER, of exercise of calcium and negative Exercise Intolerance Mutation Panel and Myoglobinuria Evaluation tests some of the common possible muscle MH the of of calcium case report and one case series patients with for MH using the the case of patients had abnormal calcium and the that MH was by statin No genetic testing was nor did any of the report clinical episodes of MH during the of the history of ER, MH, positive CHCT and polymorphisms in three genes associated with skeletal muscle calcium this patient not agents in the Although intravenous propofol are as part of metabolic and renal infusion can be of propofol especially in intensive care unit propofol may be in other neuromuscular is no evidence to that propofol is in MHS case how MH is likely to have environmental and identified as MHS have been known to unexpected or heat and exercise as well as may be diagnostic of MH in that for MH