Atrophy of type II fibres in myasthenia gravis muscle in thymectomized patients: steroid-induced change with prognostic impact.
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.
Zamecnik
Josef
J
Department of Pathology and Molecular Medicine, Charles University, 2nd Medical Faculty and University Hospital Motol, Prague, Czech Republic.
Vesely
Dan
D
Department of Pathology and Molecular Medicine, Charles University, 2nd Medical Faculty and University Hospital Motol, Prague, Czech Republic.|1st Department of Infectious Diseases, Charles University, 2nd Medical Faculty and University Hospital Bulovka, Czech Republic.
Jakubicka
Branislav
B
Department of Pathology and Molecular Medicine, Charles University, 2nd Medical Faculty and University Hospital Motol, Prague, Czech Republic.
Cibula
Adrian
A
Department of Pathology and Molecular Medicine, Charles University, 2nd Medical Faculty and University Hospital Motol, Prague, Czech Republic.
Pitha
Jiri
J
Department of Neurology, Charles University, 1st Medical Faculty, Prague, Czech Republic.|Department of Neurology, Charles University, 3rd Medical Faculty, Prague, Czech Republic.
Schutzner
Jan
J
3rd Department of Surgery, Charles University, 1st Medical Faculty and University Hospital Motol Prague, Czech Republic.
Mazanec
Radim
R
Department of Neurology, Charles University, 2nd Medical Faculty and University Hospital Motol, Prague, Czech Republic.
D000305:Adrenal Cortex Hormones / Q000494:pharmacology*; D000328:Adult; D001706:Biopsy; D006801:Humans; D008875:Middle Aged; D009133:Muscular Atrophy; D009157:Myasthenia Gravis / Q000473:pathology*; D011379:Prognosis; D013934:Thymectomy
D000305:Adrenal Cortex Hormones