Malignant Hyperthermia (MH) is an uncommon inherited skeletal muscle disorder in which skeletal muscle hypermetabolism may be triggered by commonly used anesthetic agents. The diagnosis of an acute reaction can be difficult because of nonspecific and variable manifestations in clinical findings and laboratory test changes.
Difficulties in the diagnosis of malignant hyperthermia:
(1)There is a lack of precise defining characteristics with no gold standard to aid in diagnosis.
(2) The caffeine halothane contracture test requires an open muscle biopsy and is difficult to interpret due to the absence of recognized gold standard for diagnosis.
(3) Molecular diagnostic tests are still under development.
(4) An MH susceptible person may not consistently develop an MH event after an exposure to MH-triggering anesthetics.
(5) The inheritance appears to be autosomal dominant, but penetrance is variable.
|
Process |
Indicator |
Points |
|
rigidity |
generalized muscular rigidity (in absence of shivering due to hypothermia, or during or immediately following emergence from inhalational general anesthesia. |
15 |
|
|
masseter spasm shortly following succinylcholine administration |
15 |
|
muscle breakdown |
elevated creatine kinase > 20,000 IU/L after anesthetic that included succinylcholine |
15 |
|
|
elevated creatine kinase > 10,000 IU/L after anesthetic without succinylcholine |
15 |
|
|
cola colored urine in perioperative period |
10 |
|
|
myoglobin in urine > 60 µg/L |
5 |
|
|
myoglobin in serum > 170 µg/L |
5 |
|
|
blood, plasma or serum potassium > 6 mEq/L in the absence of renal failure |
3 |
|
respiratory acidosis |
PETCO2 > 55 mm Hg with appropriately controlled ventilation |
15 |
|
|
arterial PaCO2 > 60 mm Hg with appropriately controlled ventilation |
15 |
|
|
PETCO2 > 60 mm Hg with spontaneous ventilation |
15 |
|
|
arterial PaCO2 > 65 mm Hg with spontaneous ventilation |
15 |
|
|
inappropriate hypercarbia (in anesthesiologist's judgment) |
15 |
|
|
inappropriate tachypnea |
10 |
|
temperature increase |
inappropriately rapid increase in temperature (in anesthesiologist's judgment) |
15 |
|
|
inappropriately increased temperature > 38.8 °C (101.8 °F) in the perioperative period (in the anesthesiologist's judgment) |
10 |
|
cardiac involvement |
inappropriate sinus tachycardia |
3 |
|
|
ventricular tachycardia or ventricular fibrillation |
3 |
|
other conditions |
arterial base excess more negative than -8 mEq/L |
10 |
|
|
arterial pH < 7.25 |
10 |
|
|
rapid reversal of MH signs of metabolic and/or respiratory acidosis with IV dantrolene |
5 |
|
family history |
positive MH family history in relative of first degree |
15 |
|
|
positive MH family history in relative not of first degree |
5 |
|
other conditions used for susceptibility only |
positive MH family history together with another indicator from the patient's own anesthetic experience other than elevated resting serum creatine kinase |
10 |
|
|
resting elevated serum creatine kinase (in patient with a family history of MH) |
10 |
Scoring rules:
(1) if no indicator is present for a process, then 0 is assigned
(2) if more than indicator is present for a process (except the "other conditions"), the maximum score is used
(3) family history is used to determine malignant hyperthermia susceptibility only and is not included in the event raw score
(4) "other conditions used for susceptibility only" is not included in the event raw score
(5) "other conditions" are added without regard to double-counting
(6) the susceptibility score consists of the (score for highest ranking MH event) + score for family history + score for "other conditions used for susceptibility only"; I interpret this as the maximum event for raw score (up to 15) rather than the raw score itself; the maximum sum of maximum family history score (maximum 15) and all of possible other scores (maximum 20) is 35
raw score for event =
= (maximum score for rigidity) + (maximum score for muscle breakdown) + (maximum score for respiratory acidosis) + (maximum score for temperature increase) + (maximum score for cardiac involvement) + (sum of all "other conditions" scores)
score for susceptibility =
= (score for highest ranking MH event) + (maximum score for family history) + (sum of all "other conditions used for susceptibility only" scores)
Interpretation:
• minimum raw score: 0
• maximum raw score: 15 + 15 + 15 + 15 + 3 + 25 = 88
• maximum susceptibility score: 15 + 35 = 50
• The assigned rank represents a lower bound on the likelihood of malignant hyperthermia; it is a qualitative indicator only.
• The scoring system is intended to aid in research rather than for use by the clinician.
|
Raw Score Range |
MH Rank |
Description of Likelihood |
|
0 |
1 |
almost never |
|
3 - 9 |
2 |
unlikely |
|
10 - 19 |
3 |
somewhat less than likely |
|
20 - 34 |
4 |
somewhat greater than likely |
|
35 - 49 |
5 |
very likely |
|
>= 50 |
6 |
almost certain |
Purpose: To suspect malignant hyperthermia from clinical and laboratory findings.
Specialty: Anesthesiology
Objective: clinical diagnosis, including family history for genetics, severity, prognosis, stage
ICD-10: T88.3,
