Report of a case of necrotizing autoimmune myopathy with thymoma-associated myasthenia gravis

Abstract

Purpose: Myasthenia gravis (MG) is an autoimmune disease and closely related to thymoma. Inflammatory myopathy may accompany with other autoimmune diseases. However, concurrence of inflammatory myopathy and MG is very rare. Necrotizing autoimmune myopathy (NAM), a rare form of inflammatory myopathy, is characterized by necrosis and regeneration of myocytes in proximal muscles without significant inflammation. The aim of the study was to report a rare case of NAM and concomitant thymoma-associated MG after thymectomy.

Materials and methods/results: A 27-year-old female patient presented with muscle soreness and weakness in four limbs. Eyelid fatigue and neostigmine tests were negative, and no ptosis was found but the electromyographic examination (EMG) showed myogenic damage and a gradual decrease in the amplitude (20%) of EMG activities evoked by repetitive electrical stimulation. Antibodies against AChR and increased titer of creatine kinase were detected and plaque-like signals in both legs were found in magnetic resonance imaging. Myositis-related antibodies were negative but necrotic myocytes without inflammatory cell infiltration, and MHC-1 positive muscle fibers were found in muscle biopsy. Pathological examination confirmed anterior mediastinal B2 type thymoma. Five weeks after thymectomy, she started to show typical MG symptoms. No recurrence of thymoma was found but immunoassay showed a higher titer of AChR-Ab. Myositis-related antibodies negative necrotizing autoimmune myopathy (NAM) was reported to be associated with thymoma-associated MG.

Conclusions: The patient showed symptoms related NAM but developed MG-related symptoms only after thymectomy. The mechanisms for the phenomena may be related to immune dysfunction associated with thymoma.

Keywords:

• Inflammatory myopathy
• necrotizing autoimmune myopathy
• thymoma
• myasthenia gravis

Acknowledgments

The authors thank Ms. Z. Li for her technical support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors’ contributions

XZ collected the clinical data, GH performed the pathological examination, and GH and DY wrote the manuscript.

Consent for publication

The written informed consent was obtained from the patient for the publication of this case report and accompanying images.

Additional information

Funding

This case report was supported by National Natural Scientific Foundation of China Grant 81760202 and Jiangxi Provincial People’s Hospital grant 2019-009.