Open AccessAtrophy of type II fibres in myasthenia gravis muscle in thymectomized patients: steroid‐induced change with prognostic impact
Author(s) -
Zamecnik Josef,
Vesely Dan,
Jakubicka Branislav,
Cibula Adrian,
Pitha Jiri,
Schutzner Jan,
Mazanec Radim
Publication year - 2009
Publication title -
journal of cellular and molecular medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.44
H-Index - 130
eISSN - 1582-4934
pISSN - 1582-1838
DOI - 10.1111/j.1582-4934.2008.00431.x
Subject(s) - myasthenia gravis , atrophy , muscle atrophy , thymectomy , steroid , medicine , hormone
Selective atrophy of type II muscle fibres has been long recognized as an enigmatic but consistent feature of myasthenia gravis (MG) muscle; however, the pathophysiology and the mechanism of that change have remained obscure. In the present study, the results of histomorphometric analysis performed on muscle biopsies from 207 thymectomized seropositive MG patients were correlated with clinical features of MG to demonstrate possible pathophysiological associations and potential prognostic impact. The atrophy of type II fibres was verified in 35 cases (16.9%), being more pronounced in fibres of IIB subtype. It was neither significantly associated with the duration and severity of MG nor with the age of the patients. On the other hand, we demonstrated that the atrophy associated with long‐term treatment with corticosteroids, and correlated with increasing doses. Thus, we suppose that the atrophy of type II muscle fibres in seropositive MG is steroid induced rather than MG‐associated event. Although the MG patients with atrophy of type II fibres did not differ from the remaining MG cases in terms of improvement in the disease during the follow‐up period, our analysis provides clear evidence that they presented a significantly slower tendency to reach an asymptomatic state after thymectomy. Therefore, the steroid‐induced atrophy of type II fibres in MG muscle might be considered to be an unfavourable prognostic factor.