Juvenile myasthenia gravis in Norway: A nationwide epidemiological study.
BACKGROUND
The aim of this study was to assess the incidence rate and prevalence of autoimmune myasthenia gravis (MG) among children in Norway.


METHODS
This retrospective population-based study was performed in Norway from January 2012 to December 2013. Cases of juvenile MG (JMG) with onset < 18 years were identified through searches in coding systems of electronic patient records at the 15 main hospitals in Norway from 1989 to 2013. In addition, the acetylcholine receptor antibody database at Haukeland University Hospital and the clinical nationwide MG database at Oslo University Hospital were searched for cases of JMG. Diagnosis and age at onset were verified through medical records. Incidence and prevalence rates were calculated using the Norwegian population as reference.


RESULTS
In total 63 unique JMG cases were identified. This corresponds to an average annual incidence rate of 1.6 per million. Incidence rate was stable over the study period. Prevalence of JMG was 3.6-13.8 per million. Females constituted the majority of JMG cases (55 vs 8 males). The risk of JMG was higher among females both in the postpubertal and prepubertal group (p < 0.001 and p = 0.02, respectively).


CONCLUSIONS
This study confirms the rarity of JMG in Norway, especially among males, and shows a stable incidence rate over the last 25 years.
Department of Neurology, Oslo University Hospital, Oslo, Norway; Institute of Clinical Medicine, University of Oslo, Oslo, Norway. Electronic address: t.h.popperud@medisin.uio.no.
T H
TH
Popperud
Department of Neurology, Oslo University Hospital, Oslo, Norway.
M I
MI
Boldingh
Oslo Centre for Biostatistics and Epidemiology, Research Support Services, Oslo University Hospital, Oslo, Norway.
C
C
Brunborg
Department of Neurology, Akershus University Hospital, Lørenskog, Norway.
K W
KW
Faiz
Department of Clinical Medicine, University of Bergen, Bergen, Norway.
A T
AT
Heldal
Department of Neurology, Oslo University Hospital, Oslo, Norway.
A H
AH
Maniaol
Department of Neurology and National Neuromuscular Centre, University Hospital of North Norway, Tromsø, Norway; Department of Clinical Medicine, UiT - The Artic University of Norway, Tromsø, Norway.
K I
KI
Müller
Department of Clinical Neuroscience for Children, Section for Child Neurology, Oslo University Hospital, Oslo, Norway; Unit for Hereditary and Inborn Neuromuscular Disorders, Department of Neurology, Oslo University Hospital, Oslo, Norway.
M
M
Rasmussen
Department of Clinical Medicine, University of Bergen, Bergen, Norway; Department of Pediatrics, Stavanger University Hospital, Stavanger, Norway.
K
K
Øymar
Department of Neurology, Oslo University Hospital, Oslo, Norway; Institute of Clinical Medicine, University of Oslo, Oslo, Norway.
E
E
Kerty
D000293:Adolescent; D001323:Autoantibodies / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D016208:Databases, Factual; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D009157:Myasthenia Gravis / Q000453:epidemiology*; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D011950:Receptors, Cholinergic / Q000276:immunology; D012189:Retrospective Studies; D012737:Sex Factors
D001323:Autoantibodies; D011950:Receptors, Cholinergic
Frequency; Incidence; Juvenile myasthenia gravis; Prevalence