163-1 Myasthenia/Thymoma

Figure 1. Ptosis OS Pre-tensilon

Figure 2. Positive tensilon test

Figure 3. Ptosis OS Post-tensilon

Figure 4 CT mid-thorax thymic mass (arrows)

Figure 5 CT Mid-thorax thymic mass (arrows)

Thymic hyperplasia in AChR antibody positive MG Mantle of B cells surrounding follicular dendritic cells, immune complexes and plasma cells Thymic myoid cells express fetal type AChRs Fluorescein-labelled troponin antibody Rhodamine labelled AChR antibody Schluep et al., Ann Neurol 1987

acetylcholine receptor antibodies are present in 85% Neuromuscular junction in Myasthenia Gravis acetylcholine receptor antibodies are present in 85% of MG patients and cause AChR loss Mechanisms Adult AChR a b d ACh C’-mediated lysis cross-linking blocking e e nerve terminal C’ acetylcholine receptors muscle fibre

Neuromuscular Junction in Myasthenia Gravis antibodies to MuSK in ~ 7% of patients blood-brain barrier voltage-gated potassium channels (VGKC) voltage-gated sodium channels MuSK – an endplate transmembrane protein nerve terminal voltage-gated calcium channels (VGCC) acetylcholine receptors (AChR) muscle-specific kinase (MuSK) rapsyn

MuSK antibody positive Myasthenia Gravis aged 16 years Electromyography: R frontalis and orbicularis oculi no spontaneous activity no motor units under voluntary control no activity on nerve stimulation R orbicularis oris few very small units (max ampl 50uV) normal profile (duration 5msec; not polyphasic)

MuSK antibody positive Myasthenia Gravis aged 20 years

in > 90% of LEMS patients and cause VGCC loss Neuromuscular junction in Lambert-Eaton Myasthenic Syndrome Antibodies to voltage-gated Ca++ channels (VGCCs) present in > 90% of LEMS patients and cause VGCC loss α 2 g out a 1 in d nerve terminal nerve terminal b P/Q-type voltage-gated calcium channels (VGCCs) Mechanism Cross-linking of VGCCs by antibody acetylcholine receptors muscle fibre

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