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Malignant Hyperthermia Versus Thyroid Storm in a
Patient With Symptomatic Graves Disease: A Case
Sara M. Strowd, MD, MPH, Michael B. Majewski, MD, and Jennifer Asteris, CRNA
Malignant hyperthermia and thyroid storm are intraoperative emergencies with overlapping
symptoms but different treatment protocols. We faced this diagnostic dilemma in a 25-yearold patient with symptomatic hyperthyroidism, elevated free T3 and free T4, and low thyroidstimulating hormone from Graves disease despite treatment with propranolol 80 mg daily and
methimazole 40 mg every 8 hours. During thyroidectomy, he developed hyperthermia and hypercarbia without tachycardia. When the rate of rise of Paco2 and temperature accelerated, we
treated the patient for malignant hyperthermia, a diagnosis subsequently confirmed by genetic
testing. (A&A Case Reports. 2017;XXX:00–00.)
alignant hyperthermia (MH) and thyroid storm
are perioperative emergencies that may present
with similar signs and symptoms. MH is an autosomal dominant pharmacogenetic disorder with an estimated incidence of episodes during anesthesia ranging from
1:10,000 to 1:250,000.1 The generally accepted prevalence
is thought to be 1:50,000.2 The resulting hypermetabolic
sequela requires immediate treatment to halt the reaction,
or organ failure and death will ensue. Unfortunately, the
presenting symptoms share many similarities with thyroid
storm. Because the management of these crises is drastically different, proper rapid identification is essential. We
encountered this dilemma in a patient with poorly controlled hyperthyroidism undergoing a total thyroidectomy.
Hyperthermia, hypertension, metabolic acidosis, and tachycardia can be seen in both, but rapidly rising arterial carbon
dioxide (Paco2) and temperature and muscle rigidity suggest a diagnosis of MH over thyroid storm.
Written consent was obtained from the patient for this
case report.
A 25-year-old, 82-kg man with a history of hyperthyroidism and Graves disease presented for a total thyroidectomy
because of inadequate medical management despite propranolol 80 mg by mouth daily and methimazole 40 mg by
mouth every 8 hours. His symptoms included palpitations,
shaking, heat intolerance, and exophthalmos. The patient
never had anesthesia, but both parents had experienced
general anesthesia several times. There was no family history of anesthetic complications.
On the morning of surgery, he took his methimazole
40 mg and propranolol 80 mg. Preoperative vitals were
heart rate (HR) 85 beats per minute, respiratory rate (RR)
From the Department of Anesthesiology, Loyola University Medical Center,
Maywood, Illinois.
Accepted for publication August 30, 2017.
Funding: None.
The authors declare no conflicts of interest.
Address correspondence to Sara M. Strowd, MD, MPH, Department of
Anesthesiology, Loyola University Medical Center, 2160 S. First Ave,
Maywood, IL 60153. Address e-mail to
Copyright © 2017 International Anesthesia Research Society
DOI: 10.1213/XAA.0000000000000639
18 breaths per minute, noninvasive blood pressure 138/98
mm Hg, peripheral capillary oxygen saturation 100%, and
oral temperature (T) 36.9°C. Preoperative thyroid studies
4 months earlier showed free T3 of 1782 pg/dL and free
T4 of 3.8 ng/dL. Two weeks before surgery, the thyroidstimulating hormone was <0.01 μIU/mL and free T3 of
440 pg/dL.
Midazolam 2 mg was administered intravenously (IV)
for extreme anxiety. Anesthesia was induced IV with fentanyl 100 μg, lidocaine 100 mg, propofol 200 mg, and succinylcholine 100 mg. A depolarizing muscle relaxant was
used to avoid residual neuromuscular blockade and facilitate intraoperative recurrent laryngeal nerve monitoring.
At no point was a nondepolarizing muscle relaxant used.
During direct laryngoscopy, the provider noted that the
patient’s jaw was “a little rigid” but was able to open the
patient’s mouth and intubation was otherwise uneventful.
After intubation, vital signs were HR 71, RR 12, noninvasive
blood pressure 134/73 mm Hg, peripheral capillary oxygen
saturation 95%, axillary T 36.3°C, and Etco2 45 mm Hg.
The ventilator settings on 100% (Fio2: 1.0) were tidal volume (TV) 550 mL, RR 12, and minute volume (MV) 6.6 L/
min. Within 15 minutes of induction, the TV was increased
to 675 mL (MV: 8.1 L/min) and Fio2 was decreased to 0.5.
These settings were maintained for the next 45 minutes.
General anesthesia was provided with desflurane in an air/
oxygen mixture and a remifentanil infusion. No warming
blanket or fluid warmer was used.
Approximately 1 hour into the case, T had risen to 37.4°C.
The RR was increased to 14 (MV: 9.4 L/min) to keep the
Etco2 in the low-to-mid 40s mm Hg. Thirty minutes later,
TV was increased to 700 and RR to 16 (MV: 11.2 L/min)
to keep Etco2 45 mm Hg. T at this time was 37.9°C. Blood
pressure and HR remained unchanged. At this point, there
was concern for a hypermetabolic reaction and help was
called into the room. Over the next 20 minutes, both the
temperature and Etco2 rose more rapidly, and the patient
was presumed to have MH. Volatile anesthetics were discontinued; a radial arterial line and two 16G peripheral IVs
were inserted; 100% Fio2 was administered; and dantrolene
2.5 mg/kg IV was given (Revonto; US WorldMeds, LLC,
Louisville, KY). A new ventilator with a clean circuit was
brought into the room and connected to the patient. The
axillary T peaked at 39.2°C and Etco2 peaked at 95 mm Hg
XXX 2017 • Volume XXX • Number
Copyright © 2017 International Anesthesia Research Society. Unauthorized reproduction of this article is prohibited.
despite MV 18 L/min. The initial arterial blood gas (ABG)
showed pH 7.13, Paco2 92 mm Hg, Pao2 410 mm Hg, K+ 4.9
mEq/L, and bicarbonate 30 mEq/L. At this time, the patient
developed tachycardia up to 110s and became hypotensive
with a blood pressure nadir of 59/30. The patient received
phenylephrine 600 μg IV in divided doses and tromethamine (THAM) solution 500 mL IV. There was rapid resolution of the hypotension and tachycardia. The patient’s groin
and axilla were packed with ice, and a Foley catheter was
placed. The color of the urine was not noted by the staff.
Within 10 minutes, the ABG improved to a pH 7.32, Paco2
50 mm Hg, Pao2 488 mm Hg, K+ 5.0 mEq/L, and bicarbonate 25 mEq/L. After 30 minutes, the patient’s blood gas
values were normal. During the resuscitation, furosemide
40 mg, calcium chloride 2 g, and mannitol 12.5 g were also
administered IV. The surgery was aborted after completion
of a right hemithyroidectomy including the isthmus.
The patient was transferred to the intensive care unit
intubated and sedated. He was continued on a dantrolene
protocol for 24 hours. He was extubated the following
morning, and the remainder of his postoperative course
was uncomplicated. Serum myoglobin and creatine kinase
peaked at >10,000 ng/mL and 17,995 U/L on postoperative
day #0, respectively. On discharge, the patient displayed
no ill effects; his creatine kinase was downtrending; he was
neurologically intact; and he presented no evidence of renal
failure, hyperkalemia, or rhabdomyolysis. Subsequent gene
sequencing revealed a mutation (6757 C>T) causing an
amino acid substitution (His2253Tyr) in the RYR1 receptor
that has been confirmed in the literature to be present in
1 other patient with MH.3 Subsequent completion thyroidectomy was accomplished without incident under total IV
anesthesia without triggering agents.
MH, a well-known but rare reaction to volatile anesthetics and succinylcholine, requires immediate diagnosis and
treatment to prevent severe morbidity and mortality. Many
of the clinical symptoms of MH are also manifestations of
thyroid storm, another medical emergency requiring a different unique management. Early identification of MH is
crucial to patient survival, because early removal of triggering agents and administration of dantrolene will interrupt the hypermetabolic reaction and cause resolution of
symptoms. The classic symptoms of MH (hyperthermia,
hypercapnia, tachycardia, and muscle rigidity) have significant similarities with that of thyroid storm (hypertension,
hyperthermia, and tachycardia), which can lead to delayed
diagnosis and treatment, or incorrect diagnosis altogether.
Our patient had a preoperative history of Graves disease,
including palpitations, heat intolerance, and hypertension,
that was poorly controlled despite propranolol (80 mg by
mouth daily) and very high doses of methimazole (40 mg
by mouth 3 times daily). The patient’s calculated Burch and
Wartofsky4 score was 40, which is suggestive of impending
thyroid storm. Because of this overlap of symptoms and
the severity of his Graves disease, additional laboratory
information was originally sought, but the accelerating rise
in Etco2 and temperature caused us to initiate therapy for
probable MH before the ABG results.
In retrospect, the masseter muscle rigidity present on
induction, although with a low positive predictive value
for MH, was the earliest suggestion of MH. The presence of masseter muscle rigidity does correlate with an
incidence of MH of approximately 15%1 according to
blood gas analysis and as high as 59% in children based
on muscle biopsy,5 although only 5 of the 41 biopsy-confirmed MH-susceptible patients went on to develop MH
symptoms after induction with volatile agents and/or
succinylcholine. Despite the majority of studies surrounding masseter muscle rigidity being performed in children,
masseter spasm in the setting of hyperthermia or hypercapnia, escalating minute ventilation, or any other symptom of MH should lead to immediate further investigation,
if not treatment, for MH.
Our patient did not develop tachycardia until late in the
presentation at which time he also developed severe hypotension. The absence of tachycardia, especially in the setting
of perioperative β-blockade and/or remifentanil infusion,
did not suggest either diagnosis. Higher HRs, according
to the point system developed by Burch and Wartofsky,4
make thyroid storm more likely, especially in patients with
a history of prior hyperthyroid symptoms. However, these
symptoms can also be present in MH and therefore do not
assist in discerning the 2 diagnoses.
The presentation of thyroid storm is not determined by
thyroid function laboratory results; results in patients with
thyroid storm may be similar to patients with compensated thyrotoxicosis.6 Likewise, massively elevated creatine
kinase and myoglobin strongly suggest muscle injury like
that seen in MH, but these laboratory results require more
time to obtain than allowed in a crisis. The ABGs showed
severe acidemia and severe hypercapnia, both of which
strongly suggest MH over thyroid storm. The hypermetabolic state from thyroid storm, although capable of causing
acidemia, is predominantly metabolic in origin as opposed
to the simultaneous metabolic and respiratory acidosis that
develop in MH.
The use of THAM for the correction of metabolic acidosis is debatable. However, the use of sodium bicarbonate
rather than THAM could have worsened the hypercapnia
and acidosis. THAM is also a diuretic that should improve
the excretion of potassium and myoglobin. It is also able to
buffer the excess carbon dioxide and theoretically improve
the acidemia.7
Other symptoms which our patient did not develop that
would suggest thyroid storm over MH include unexplained
jaundice, heart failure, and severe central nervous system
effects such as seizures and coma.5 The short episode of
hypotension was attributed to severe acidemia rather than
heart failure, as suggested by its rapid resolution with
dantrolene, THAM, and phenylephrine. In addition, it is
worth mentioning that a diagnosis of pheochromocytoma
also shares many symptoms with both MH and thyroid
storm. Our patient did not demonstrate the HR lability
or hypertension after anxiolysis or induction of anesthesia that is typically seen in a patient with undiagnosed
In conclusion, we examined the key points that help
resolve diagnosing intraoperative MH from thyroid storm.
The insidious rise of the temperature could have been
Copyright © 2017 International Anesthesia Research Society. Unauthorized reproduction of this article is prohibited.
from either syndrome, but the muscle rigidity on induction and the sudden acceleration of the hyperthermia as
well as the severe respiratory acidosis suggested the presence of MH. In contrast, the patient displayed no signs of
heart failure and his acidosis was more severe than that
seen in thyroid storm. Rapid differentiation between MH
and thyroid storm is critical because the management of
each is unique. E
Name: Sara M. Strowd, MD, MPH.
Contribution: This author helped write, edit, and format the
Name: Michael B. Majewski, MD.
Contribution: This author helped write and edit the manuscript.
Name: Jennifer Asteris, CRNA.
Contribution: This author helped write and edit the manuscript.
This manuscript was handled by: Raymond C. Roy, MD.
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ryanodine 1 gene for malignant hyperthermia causative mutations by high resolution melt curve analysis. Anesth Analg.
4. Burch HB, Wartofsky L. Life-threatening thyrotoxicosis. Thyroid
storm. Endocrinol Metab Clin North Am. 1993;22:263–277.
5.O’Flynn RP, Shutack JG, Rosenberg H, Fletcher JE. Masseter
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pediatric patients. An update on management and diagnosis.
Anesthesiology. 1994;80:1228–1233.
6.De Leo S, Lee SY, Braverman LE. Hyperthyroidism. Lancet.
7. Nahas GG, Sutin KM, Fermon C, et al. Guidelines for the treatment of acidaemia with THAM. Drugs. 1998;55:191–224.
XXX 2017 • Volume XXX • Number
Copyright © 2017 International Anesthesia Research Society. Unauthorized reproduction of this article is prohibited.
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