Malignant hyperthermia (MH) can be a life-threatening condition and diagnosing it can be a challenge. A chart review by an international research team led by Columbia University Medical Center, New York City, and sponsored by the Malignant Hyperthermia Association of the United States (MHAUS) has concluded that approximately 70% of International Classification of Diseases (ICD)-9– and ICD-10–coded MH diagnoses in hospital discharge records refer to incident MH episodes or MH susceptibility.
As Teeda Pinyavat, MD, explained, ICD-9 codes for MH were introduced in 1997. Previous research at Columbia sought to determine the incidence and prevalence of MH. “This was a follow-up study to see if these ICD-9 codes were accurate,” said Dr. Pinyavat, who is an assistant professor of anesthesiology at Columbia.
To that end, the researchers assembled an expert panel of anesthesiologists—all of whom are MHAUS hotline consultants—which reviewed medical records for 47 patients with a discharge diagnosis of MH based on ICD-9 and ICD-10 codes. The records were from six tertiary care centers in North America and the patients had been discharged between Jan. 1, 2006 and Dec. 31, 2008. “We looked through every single note for the entire admission with a team of experts,” she explained. “There were five of us in total, but at least three of us would travel to each center and do the record review.” All cases were categorized as possible MH, probable MH, fulminant MH, history of MH (family or personal) or “other.”
As Dr. Pinyavat reported at the 2014 annual meeting of the International Anesthesia Research Society (abstract S-223), the patients’ mean age was 40 years; 51% were women. A surgical procedure and general anesthesia were documented in 68% of cases. Only 11 of the 47 (23.4%) cases were deemed to be an incident case of possible, probable or fulminant MH by the expert panel. “We thought this number would be higher, but was actually less than 25% of the events,” she said.
Family and personal history of MH accounted for 46.8% of cases, whereas high fever without evidence of MH during admission comprised another 23.4%. “And in three records we really couldn’t figure out any reason at all for the coding,” Dr. Pinyavat said. It was also found that dantrolene was given in 81% of MH cases. All patients judged to have an incident MH event survived to discharge.
“We also found that the patients who were falsely labeled as having MH were, on the whole, sicker than the others,” she added. “And most of them did not have a surgical procedure. By comparison, the actual incident MH cases were largely ASA [American Society of Anesthesiologists physical status] 1 and 2, and all of them had a surgical procedure and surgical anesthesia trigger.”
Given these results, the researchers have begun to consider alternative ways of identifying true incidents of MH. “If we only look at the patients who had surgery, we improve a little bit on the incidence of incident MH, to 35%,” Dr. Pinyavat explained. “And if you could somehow link to a pharmacy database and find out who got dantrolene, those two things together—surgery and dantrolene administration—would be very powerful in finding actual MH cases in administrative databases.
“But if you’re going to use ICD-9 and ICD-10 information, like any disease you really need to know what you’re looking for, because there are a lot of coding errors.”
Session moderator George Hall, MB, BS, PhD, professor of anesthesia at St. George’s, University of London, United Kingdom, urged caution when using dantrolene as a marker for MH. “Dantrolene will lower core temperature in any situation in which thermogenesis is occurring in skeletal muscle,” he said. “We’ve used it occasionally in things like neuroleptic malignant sy ndrome and in patients on antipsychotic medications.
“Some anesthesiologists might believe, ‘Well, we’ve got a response to dantrolene, therefore the patient has MH.’ Not necessarily. If you’ve got a response to dantrolene, it just means heat was being produced in muscle,” Dr. Hall said.