Subgroup Classification of Myasthenia Gravis.

Sir,

I read the article by Samal and colleagues in the Annals of Indian Academy of Neurology, Jan-Feb issue 2020, Vol. 23, Issue 1, entitled “MuSK (Muscle Specific Kinase) Positive Myasthenia: Grave Prognosis or undue Prejudice”[1] wherein the authors have compared the demographic and clinical characteristics, treatment response, and outcome of myasthenia gravis (MG) with MuSK antibodies with anti-acetylcholine receptor (AChR) antibodies and seronegative MG (SNMG).

The authors found no differences in the three subtypes in all parameters. Besides, I am sorry to say that to draw such a conclusion from this study, which is a retrospective study, a small sample size in which different treatment modalities are used, would not be appropriate. Autoantibodies against acetylcholine receptors (AChR), MuSK, and lipoprotein-related protein 4 (LRP4) are well-established as sensitive and specific diagnostic markers and pathogenic factors, and these autoantibodies are instrumental for subgrouping patients with MG. A prerequisite for optimum diagnosis and treatment, therefore, is access to antibodies testing.

The thymus is thought to play an important pathogenetic role in AChR antibody-positive (AChr +) in younger patients, whose myasthenia often improves with early thymectomy.[2] In these cases, muscle like myeloid cells in the thymic medulla are implicated in the perivascular infiltration by lymph node T-cell areas and germinal centers, however, in SNMG the thymic histology is frequently reported within “involuted” or “atrophic.”[3]

MuSK antibodies are mainly IgG4 unlike the IgG1 and IgG3 AChR antibodies and are not complement activating. The observations of the present study are not in line with the previously published studies.[245] Clifford and his colleagues in their study have provided enough evidence that thymectomy may not be associated with an increased likelihood of a favorable outcome in MuSK positive MG.[6] Given the low likelihood that a future randomized, controlled trial will be performed in MuSK-MG, the data from this study may help to inform treatment decisions. A study by Samal and colleagues,[1] has not even reviewed the literature extensively and skipped certain major studies that have contributed to the understanding of the abovementioned research.

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