Thymic Lesions in Myasthenia Gravis: A Clinicopathological Study from India

Article type: Research Article

Authors: Nishadham, Vikas^a | Bardhan, Mainak^{a; b} | Polavarapu, Kiran^{a; c} | Vengalil, Seena^a | Nashi, Saraswati^a | Menon, Deepak^a | Ganaraja, Valakunja Harikrishna^a | Preethish-Kumar, Veeramani^a | Valasani, Ravi Kiran^a | Huddar, Akshata^a | Unnikrishnan, Gopi Krishnan^a | Thomas, Abel^a | Saravanan, Akshaya^d | Kulanthaivelu, Karthik^d | Nalini, Atchayaram^{a; *} | Nandeesh, Bevinahalli Nanjegowda ^{e; *}

Affiliations: [a] Department of Neurology, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, Karnataka, India | [b] ICMR-National Institute of Cholera and Enteric Diseases (NICED), Kolkata, West Bengal, India | [c] Children’s Hospital of Eastern Ontario Research Institute, Department of Medicine, Division of Neurology, The Ottawa Hospital, Brain and Mind Research Institute, University of Ottawa, Ottawa, ON, Canada | [d] Neurointerventional and Imaging, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, Karnataka, India | [e] Neuropathology, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, Karnataka, India

Correspondence: [*] Correspondence to: Dr. Bevinahalli N Nandeesh, Associate Professor, Department of Neuropathology, National Institute of Mental Health and Neurosciences, Bengaluru –560029, India. E-mail: nandeeshbn@gmail.com and Dr. Atchayaram Nalini, Professor of Neurology, Neuromuscular specialist, Department of Neurology, Neuroscience Faculty Center, National Institute of Mental Health and Neurosciences, Bengaluru –560029, India. Tel.: +91 80 26995139; Fax: +91 80 26568430; E-mail: atchayaramnalini@yahoo.co.in.

Abstract: Background and Objectives:Thymic pathology is common in Myasthenia Gravis(MG) and plays a crucial role in its pathogenesis and clinical outcome. This study aims to discuss the clinicohistopathological spectrum of thymic lesions in MG. Methods:In this retrospective study, MG patients who underwent thymectomy from 2011 to 2020 were included. Clinical, radiological, serological, and histopathological details are described. Results:Of 83 patients(F = 45; M = 38), 7(8%) had ocular myasthenia, and the remaining 76(92%) had the generalized form. At onset, the median age was 36 years(M = 44; F = 31). AChR antibody was positive in 71/79 patients. RNST showed decrement response in 68/78 patients. The histopathological study demonstrated thymoma in 44(53%), thymic hyperplasias [32(38%)], involuted thymus [5(6%)], thymic cyst (1) and thymic lipoma (1). WHO grading of thymoma: B2- 48%, AB-18%, B-18%, B3-14%, A-2.3%. In these, capsular infiltration was noted in 11/44, 9 had focal and 2 had diffuse infiltration. Active germinal centers were present in 20/32 patients with thymic hyperplasia and 4/44 with thymoma. Thymomas were predominant in males and thymic hyperplasia in females. The age of onset and antibody positivity rate was higher in thymoma patients. Conclusion:In our cohort, there is a female preponderance. Thymoma was the commonest pathology followed by hyperplasia. We observed earlier onset of myasthenia in females. AChR antibody positivity rate was more frequent in thymomas. This study indicates that clinico-radiological evaluation adequately supported by serology and histopathology can effectively recognize the type of thymic pathology that can guide these patients’ treatment planning, management, prognosis and follow-up.

Keywords: Myasthenia gravis, thymoma, thymic hyperplasia, thymectomy, histopathology

DOI: 10.3233/JND-210785

Journal: Journal of Neuromuscular Diseases, vol. 9, no. 3, pp. 411-422, 2022