title: Myasthenia gravis with muscle specific kinase antibodies mimicking amyotrophic lateral sclerosis.
abstract: Muscle-specific kinase (MuSK) myasthenia gravis (MG) is hallmarked by the predominant involvement of bulbar muscles and muscle atrophy. This might mimic amyotrophic lateral sclerosis (ALS) presenting with bulbar weakness. We encountered four cases of MuSK MG patients with an initial misdiagnosis of ALS. We analyzed the clinical data of the four misdiagnosed MuSK MG patients, and investigated the presence of MuSK autoantibodies in a group of 256 Dutch bulbar-onset ALS patients using a recombinant MuSK ELISA and a standard MuSK radioimmunorecipitation assay. Clues for changing the diagnosis were slow progression, clinical improvement, development of diplopia and absence of signs of upper motor neuron involvement. No cases of MuSK MG were identified among a group of 256 bulbar ALS patients diagnosed according to the revised El Escorial criteria. A misdiagnosis of ALS in patients with MuSK MG is rare. We recommend to carefully consider the diagnosis of MuSK MG in patients presenting with bulbar weakness without clear signs of upper motor neuron dysfunction.
authors.affiliation: Department of Neurology, Leiden University Medical Center, Leiden, Netherlands; Department of Human Genetics, Leiden University Medical Center, Leiden, Netherlands. Electronic address: m.g.m.huijbers@lumc.nl.
authors.forename: Maartje G
authors.initials: MG
authors.lastname: Huijbers
authors.affiliation: Department of Neurology, Leiden University Medical Center, Leiden, Netherlands.
authors.forename: Erik H
authors.initials: EH
authors.lastname: Niks
authors.affiliation: Department of Human Genetics, Leiden University Medical Center, Leiden, Netherlands.
authors.forename: Rinse
authors.initials: R
authors.lastname: Klooster
authors.affiliation: Department of Neurology, Amsterdam Medical Center, Amsterdam, Netherlands.
authors.forename: Marianne
authors.initials: M
authors.lastname: de Visser
authors.affiliation: Department of Neurology, University Medical Center Groningen, Groningen, Netherlands.
authors.forename: Jan B
authors.initials: JB
authors.lastname: Kuks
authors.affiliation: Department of Neurology and Neurosurgery, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, Netherlands.
authors.forename: Jan H
authors.initials: JH
authors.lastname: Veldink
authors.affiliation: Department of Neurology, Zuyderland Medical Center, Heerlen, Netherlands.
authors.forename: Pim
authors.initials: P
authors.lastname: Klarenbeek
authors.affiliation: Department of Neurosciences, VIB - Vesalius Research Center, Experimental Neurology - Laboratory of Neurobiology, KU Leuven - University of Leuven, Leuven, Belgium; Department of Neurology, University Hospitals Leuven, Leuven, Belgium.
authors.forename: Philip
authors.initials: P
authors.lastname: Van Damme
authors.affiliation: Department of Neurosciences, Maastricht University, Maastricht, Netherlands.
authors.forename: Marc H
authors.initials: MH
authors.lastname: de Baets
authors.affiliation: Department of Human Genetics, Leiden University Medical Center, Leiden, Netherlands.
authors.forename: Silvère M
authors.initials: SM
authors.lastname: van der Maarel
authors.affiliation: Department of Neurology and Neurosurgery, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, Netherlands.
authors.forename: Leonard H
authors.initials: LH
authors.lastname: van den Berg
authors.affiliation: Department of Neurology, Leiden University Medical Center, Leiden, Netherlands.
authors.forename: Jan J
authors.initials: JJ
authors.lastname: Verschuuren
mesh_terms: D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000175:diagnosis; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D003951:Diagnostic Errors; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000175:diagnosis* / Q000188:drug therapy / Q000201:enzymology / Q000276:immunology*; D020794:Receptor Protein-Tyrosine Kinases / Q000276:immunology*; D011950:Receptors, Cholinergic / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D011950:Receptors, Cholinergic; C095714:MUSK protein, human; D020794:Receptor Protein-Tyrosine Kinases
keywords: Amyotrophic lateral sclerosis; IgG4; MuSK; Myasthenia gravis; Neuromuscular junction