Muscle biopsy and in vitro contracture test in subjects with idiopathic HyperCKemia.
BACKGROUND
Persistent high creatine kinase (CK) levels may reflect underlying subclinical myopathies. In most cases, pathogenesis is unknown and clinical management is unclear. Though clinically asymptomatic, these subjects are potentially susceptible to malignant hyperthermia.


METHODS
The authors analyzed 37 subjects with persistent elevation of CK without significant weakness or other neurologic symptoms. Neurologic examination was performed according to manual muscle testing. Muscle biopsy and the in vitro contracture test were performed in all subjects.


RESULTS
Twenty-three subjects (51.1%) were completely asymptomatic. The others had minor symptoms such as occasional cramps (11 subjects, 24.4%), fatigue (5 subjects, 11.1%), a combination of cramps and fatigue (5 subjects, 11.1%), and muscle pain (1 case, 2.2%). Muscle biopsy enabled precise diagnosis in 3 cases and was normal in 3 cases. The more frequent changes were variation in fiber size (31.1%), a combination of nuclear internalization and variation in fiber size (26.6%), nuclear internalization (6.6%), minor mitochondrial changes (4.4%), and neurogenic atrophy (4.4%). Immunocytochemical analysis was normal in all patients. In vitro contracture testing detected one malignant hyperthermia-susceptible and one malignant hyperthermia-equivocal subject.


CONCLUSIONS
The evidence of malignant hyperthermia susceptibility by in vitro contracture test seems to be relatively infrequent among subjects with idiopathic hyperCKemia, but the incidence of true malignant hyperthermia in idiopathic hyperCKemia is unknown. Muscle biopsy should be considered a useful, though not very sensitive, diagnostic tool in idiopathic hyperCKemia, because it enables potentially treatable disorders, such as inflammatory myopathies, to be discovered. No uniform morphologic finding typical of idiopathic hyperCKemia or malignant hyperthermia susceptibility was identified by muscle biopsy.
Malandrini
Alessandro
A
Department of Neurological and Behavioural Sciences, University of Siena, Viale Bracci 2, 53100 Siena, Italy. malandrini@unisi.it
Orrico
Alfredo
A
Gaudiano
Carmen
C
Gambelli
Simona
S
Galli
Lucia
L
Berti
Gianna
G
Tegazzin
Vincenzo
V
Dotti
Maria Teresa
MT
Federico
Antonio
A
Sorrentino
Vincenzo
V
D000293:Adolescent; D000328:Adult; D000368:Aged; D001706:Biopsy; D002648:Child; D003402:Creatine Kinase / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008305:Malignant Hyperthermia / Q000209:etiology; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000473:pathology*; D012189:Retrospective Studies; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics
D019837:Ryanodine Receptor Calcium Release Channel; D003402:Creatine Kinase