Myasthenia Gravis – a Critical Assessment of the Contribution of Muscle Biopsy Performed During Thymectomy

Czech version

Authors: J. Zámečník ¹; J. Piťha ²; J. Schützner ³; D. Veselý ^1,4; B. Jakubička ¹
Authors‘ workplace: Ústav patologie a molekulární medicíny, UK 2. LF a FN v Motole, Praha, 2Neurologická klinika, UK 1. LF a VFN, Praha, 3III. chirurgická klinika, UK 1. LF a FN v Motole, Praha, 4I. infekční klinika, UK 2. LF a FN Bulovka, Praha ¹
Published in: Cesk Slov Neurol N 2009; 72/105(2): 147-154
Category: Original Paper

Overview

Objective:
Surprisingly, structural changes o utside the ne uromuscular juncti ons were reported in limited seri es of myastheni a gravis (MG) muscles previ o usly – mainly small collecti on of interstiti al lymphocytes and atrophy of type II muscle fibers. However, the pathophysiological mechanisms remained uncle ar. We performed a systematic study on MG muscle bi opsi es to contribute to understanding of the associ ation to MG and to demonstrate possible prognostic value.

Methods:
Sternothyro id muscle bi opsies from 207 MG patients taken during thymectomy were analyzed histopathologically and by histochemistry and morphometry and correlated to the clinical fe atures and the o utcome of MG pati ents.

Results:
In 143 MG pati ents, no obvi o us pathological changes were observed in muscle bi opsi es. In 20 pati ents we observed an interstiti al infiltrati on by mature naive CD45RA+lymphocytes. The lymphocytic infiltrati on associ ated with the thymus pathology, mainly with thymoma. The morphometry disclosed selective atrophy of type II muscle fibers in 35 cases. The atrophy of type II muscle fibers was related to long‑term corticostero id tre atment and the potenti al prognostic value co uld be demonstrated for its detecti on: the MG pati ents with type II fibers atrophy presented slower tendency to re ach remissi on. Further, in 12 cases we demonstrated mild changes in mitochondri al metabolism, in 34 cases we disclosed angular atrophic fibers; no prognostic value was demonstrated for these changes.

Conclusi ons:
The previ o usly reported histopathological changes in MG muscle are rare and mostly do not represent a fe ature of the MG, rather a consequence of the thymic disorder or of the long‑term stero id therapy. The value of muscle bi opsy performed during thymectomy for the particular MG pati ent remains controversi al.

Key words:
myasthenia gravis – muscle biopsy – thymectomy – prognosis

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