PT  - JOURNAL ARTICLE
AU  - Michael Skolka
AU  - Christopher J. Lamb
AU  - Devon I. Rubin
AU  - Christopher J. Klein
AU  - Ruple S. Laughlin
TI  - Electrodiagnostic Characteristics Suggestive of Muscle-Specific Kinase Myasthenia Gravis
AID  - 10.1212/CPJ.0000000000001166
DP  - 2022 Jun 01
TA  - Neurology: Clinical Practice
PG  - 211--217
VI  - 12
IP  - 3
4099  - http://cp.neurology.org/content/12/3/211.short
4100  - http://cp.neurology.org/content/12/3/211.full
AB  - Background and Objectives Muscle-specific kinase (MuSK) antibody–positive myasthenia gravis (MuSK + MG) is a form of MG with bulbar-predominant symptoms often resistant to conventional treatments. Patients with MuSK + MG may have an electrodiagnostic (EDX) profile distinct from other MG. This study compares EDX features of MuSK + MG with acetylcholine receptor (AChR) antibody–positive MG (AChR + MG) to discern whether any unique EDX pattern exists that can aid in clinical diagnosis.Methods From January 1, 2010, through December 31, 2020, all patients with MuSK + MG at our institution were identified and randomly matched to an AChR + MG cohort in a 1:2 ratio based on sex, age at onset, and subsequently Myasthenia Gravis Foundation of America (MGFA) clinical severity for a case-control study. Each patient's clinical profile, treatment, and EDX testing were summarized and analyzed.Results Twenty-two patients with MuSK + MG (18 female) and 44 patients with AChR + MG were studied. The average symptom duration at presentation was shorter in the MuSK + MG group (4.7 years) compared with AChR + MG (10.9 years). Myotonic discharges were rare in both groups but more frequently observed in patients with MuSK + MG (10%) identified in 5 muscles in 2 patients compared with AChR + MG (2%) noted in only 1 muscle in 1 patient. Patients with MuSK + MG more often had myopathic appearing motor unit potentials (MUPs) (41% vs 30%) compared with AChR + MG. Myopathic appearing MUPs were found in milder cases of MuSK + MG (MGFA class I–IIB) compared with AChR + MG (MGFA Class IIB–V).Discussion Patients with MuSK + MG may have a recognizable EDX profile from AchR + MG that includes (1) myotonic discharges, (2) greater occurrence of myopathic appearing MUPs in clinically mild disease, and (3) symptoms leading to earlier testing.