Table 1. Classification of MG subgroups and common associated autoimmune disorders.

MG subgroup		Age of onset (years)	Muscle auto-antibodies	Thymus involvement	Affected muscles	Associated autoimmune disorder
I	Ocular	All	AChR (50%)	Rarely	Ocular	ATD
II	Early onset	<50	AChR (100%)	Hyperplasia	Generalized	ATD, SLE, type 1 DM, AAT, GCM, NMO, myositis, PRCA, autoimmune hepatitis, Sjögren’s syndrome, Addison’s disease, dermatomyositis/polymyositis, GBS
III	Late onset	>50	AChR (100%), titin (60%), RyR (14%)	Atrophy	Generalized	Hashimoto’s disease, SLE, MS
IV	Thymoma	All	AChR (100%), titin (90%), RyR (75%)	Lympho-epithelioma	Ocular, bulbar, neck, generalized	SLE, neuromyotonia, Sjögren’s syndrome, autoimmune haemolytic anemia, POEMS syndrome
V	MuSK	All	MuSK (100%)	No	Ocular, bulbar, facial, generalized	SLE, pemphigus foliaceus, pemphigus vulgaris, MS
VI	LRP4	All	LRP4 (100%)	No	Bulbar	LEMS, NMO
VII	Antibody negative	All	Low affinity ab, low ab concentration, other junction protein-ab, non-ab, heterogenous	Variable	Ocular, generalized

MG, myasthenia gravis; AchR, acetylcholine receptor; RyR, ryanodine receptor; MuSK, muscle specific tyrosine kinase; LRP4, low density lipoprotein receptor-related protein 4; ab, antibody; ATD, autoimmune thyroid disease; SLE, systemic lupus erythematosus, NMO, neuromyelitisoptica; DM, diabetes mellitus; AAT, alopecia areata totalis; GCM, giant cell myocarditis; PRCA, pure red cell aplasia; GBS, Guillain–Barre syndrome, MS, multiple sclerosis; POEMS, polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma-proliferative disorder, skin changes; LEMS, Lambert Eaton myasthenic syndrome.