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LETTER TO EDITOR
Year : 2021  |  Volume : 69  |  Issue : 2  |  Page : 528-529

Myasthenia Gravis with Thymoma and a Rare Serological Profile—Report of a Case and Review of Literature


1 Department of Pathology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Thiruvananthapuram, Kerala, India
2 Department of Neurology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Thiruvananthapuram, Kerala, India
3 Department of Imaging Sciences and Interventional Radiology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Thiruvananthapuram, Kerala, India
4 Department of Pathology, Regional Cancer Centre, Thiruvananthapuram, Kerala, India

Date of Submission14-Apr-2019
Date of Decision02-Jun-2019
Date of Acceptance12-Feb-2021
Date of Web Publication24-Apr-2021

Correspondence Address:
Rajalakshmi Poyuran
Department of Pathology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum Thiruvananthapuram, Kerala - 695 011
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.314552

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How to cite this article:
Narasimhaiah D, Sreedharan SE, Anoop A, Radhakrishnan NR, Poyuran R. Myasthenia Gravis with Thymoma and a Rare Serological Profile—Report of a Case and Review of Literature. Neurol India 2021;69:528-9

How to cite this URL:
Narasimhaiah D, Sreedharan SE, Anoop A, Radhakrishnan NR, Poyuran R. Myasthenia Gravis with Thymoma and a Rare Serological Profile—Report of a Case and Review of Literature. Neurol India [serial online] 2021 [cited 2021 May 16];69:528-9. Available from: https://www.neurologyindia.com/text.asp?2021/69/2/528/314552




Sir,

Myasthenia gravis (MG) is a neuromuscular disease of autoimmune origin characterized by autoantibodies to various components of the neuromuscular junction. In this report, a case of MG with co-occurring antibodies to muscle-specific kinase (MuSK), titin, and thymoma is presented.

A 55-year-old woman presented with binocular diplopia and fatigable ptosis of 3 months duration and reduced pitch of the voice since 2 weeks. There was no bulbar/respiratory, neck or limb weakness, or fatigability. Examination showed bilateral ptosis with external ophthalmoparesis sparing the pupils, mild neck flexion weakness, and no significant bulbar/respiratory involvement. The rest of the central nervous system and systemic examination was normal.

The routine hematological and biochemical parameters and CSF examination were within normal limits. Spontaneous/voluntary single-fiber electromyography from left frontalis muscle revealed a mean consecutive difference of 65 μs which was diagnostic of neuromuscular transmission defect. Neostigmine test was negative. Nerve conduction study, including repetitive nerve stimulation, was normal.

Patient serum was tested for antibodies against acetylcholine receptor (AChR), MuSK, and titin by ELISA. The values were: MuSK 3.6 (≥2.1 positive), titin 0.91 (>0.3 positive), and AChR 0.2 nmol/L (>0.45 nmol/L positive). Anti-thyroid peroxidase and anti-thyroglobulin antibodies were also positive. The computerized tomography of the thorax revealed a well-defined anterior mediastinal mass suggestive of thymoma [Figure 1]a. MRI of the brain was normal. The biopsy from the anterior mediastinal mass revealed a thymoma [Figure 1]b, [Figure 1]c, [Figure 1]d.
Figure 1: Imaging and histopathology of thymoma. (a) Axial contrast CT chest shows a well-defined anterior mediastinal mass (*) with heterogeneous enhancement, hypodense areas, and calcification (linear arrow) (Ao = aorta, SVC = superior vena cava, PA = pulmonary artery). (b-d) Thymoma with epithelial cells intermixed with lymphocytes (b). The epithelial cells express pan cytokeratin (c) and lymphocytes are highlighted by terminal deoxynucleotidyl transferase (d). (Hematoxylin and eosin (b), immunoperoxidase (c and d) original magnification 200×. Scale Bars for all: 50 μm)

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The patient was diagnosed to have MG with thymoma, started on cholinesterase inhibitors and prednisolone. Thymectomy revealed type AB thymoma. At the last follow-up, the patient showed improvement of ptosis and diplopia.

Thymic changes such as hyperplasia and thymoma are infrequent in MuSK-positive myasthenia gravis (MuSK-MG), unlike in AChR-positive myasthenia. There are only five previous reports of MuSK-positive, AChR-negative myasthenia associated with thymoma,[1],[2],[3],[4] making this the sixth case in the literature [Table 1]. However, in contrast to the present case, in two of the previously reported cases, the thymoma was small and detected only on histopathological examination.[1],[3]
Table 1: MuSK antibody-positive myasthenia cases with associated thymoma reported in the literature

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Moreover, our patient also had anti-titin antibodies. Co-occurrence of anti-MuSK and anti-titin antibodies is very rare and none of the previously reported MuSK-titin double-positive cases were associated with thymoma.[4] However, three of the previously reported cases of MuSK-positive MG with thymoma were not tested for anti-titin antibodies.[1],[2],[3] And in one, the status of anti-titin antibodies in two cases of MuSK-MG with thymoma was not specifically mentioned.[4]

The caveats in this report are: the use of ELISA as the assay method than the more sensitive radioimmunoprecipitation assay and the assays were not repeated multiple times.

In conclusion, a case of myasthenia with a rare serological combination of anti-MuSK and anti-titin antibodies and a thymoma is reported. It is not clear if the co-existence of MuSK and titin antibodies leads to development of a thymic neoplasm by as yet unknown pathogenetic mechanism or if this a mere coincidence. Routinely testing for titin in AChR-negative myasthenia patients may improve our understanding of the interaction between titin and non-AChR antibodies.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Saka E, Topcuoglu MA, Akkaya B, Galati A, Onal MZ, Vincent A. Thymus changes in anti-MuSK-positive and -negative myasthenia gravis. Neurology 2005;65:782-3.  Back to cited text no. 1
    
2.
Ito A, Sasaki R, Ii Y, Nakayama S, Motomura M, Tomimoto H. [A case of thymoma-associated myasthenia gravis with anti-MuSK antibodies]. Rinsho Shinkeigaku 2013;53:372-5.  Back to cited text no. 2
    
3.
Evoli A, Bianchi MR, Riso R, Minicuci GM, Batocchi AP, Servidei S, et al. Response to therapy in myasthenia gravis with anti-MuSK antibodies. Ann N Y Acad Sci 2008;1132:76-83.  Back to cited text no. 3
    
4.
Li M, Han J, Zhang Y, Lv J, Zhang J, Zhao X, et al. Clinical analysis of Chinese anti-low-density-lipoprotein-receptor-associated protein 4 antibodies in patients with myasthenia gravis. Eur J Neurol 2019;26:1296-e84.  Back to cited text no. 4
    


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