["Seronegative" myasthenia gravis and antiMuSK positive antibodies: description of Spanish series].
OBJECTIVE
Recently, the presence of antibodies to a muscle-specific tyrosine kinase (MuSK) has been reported in some patients with seronegative generalized myasthenia gravis. Our objective was to describe a group of patients who were positive for anti-MuSK antibodies.


METHODS
Detection of antibodies using a radioimmunoassay was performed in the serum of 26 patients with generalized myasthenia gravis. We identified 9 patients with anti-MuSK antibodies (MuSK+). Clinical and therapeutic data from these patients were reviewed.


RESULTS
Eight of nine patients were women aged between 20 and 40 years. Clinically, all of them showed prevalent bulbar signs, initially or during the progression of the disease. 77% of patients showed ocular involvement and 44% had symptoms of fatigability involving limbs. None of them improved upon thymectomy. Response to acetylcholinesterase inhibitors was variable. All of them responded to immunotherapy, although 30% required polytherapy.


CONCLUSIONS
The study of anti-MuSK antibodies defines a subgroup of patients, 34,61% in our series, with seronegative generalized myasthenia. This group is characterized by an homogenous clinical presentation with prevalent bulbar symptoms. The knowledge of the immunopathogenic mechanisms of anti-MuSK antibodies will allow a better understanding of both the variable response to acetylcholinesterase inhibitors and the absence of response to thymectomy in these patients.
Unidad de Enfermedades Musculares, Servicio de Neurología, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain. illa@hsp.santpau.es
Isabel
I
Illa
Jordi A
JA
Díaz-Manera
Cándido
C
Juárez
Ricard
R
Rojas-García
Laura
L
Molina-Porcel
Aitziber
A
Aleu
Jesús
J
Pradas
Eduard
E
Gallardo
D000293:Adolescent; D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000276:immunology*; D002800:Cholinesterase Inhibitors / Q000627:therapeutic use; D003131:Combined Modality Therapy; D004172:Diplopia / Q000453:epidemiology; D005121:Extremities / Q000503:physiopathology; D005221:Fatigue / Q000453:epidemiology / Q000503:physiopathology; D005260:Female; D006801:Humans; D007167:Immunotherapy; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000453:epidemiology / Q000276:immunology* / Q000628:therapy; D020794:Receptor Protein-Tyrosine Kinases / Q000276:immunology*; D011950:Receptors, Cholinergic / Q000276:immunology*; D012720:Severity of Illness Index; D013030:Spain / Q000453:epidemiology; D013934:Thymectomy; D016896:Treatment Outcome
D001323:Autoantibodies; D002800:Cholinesterase Inhibitors; D011950:Receptors, Cholinergic; C095714:MUSK protein, human; D020794:Receptor Protein-Tyrosine Kinases