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[Inclusion body myositis and neuromuscular diseases with rimmed vacuoles]
D Figarella-Branger1, J F Pellissier, J Pouget
1Service d'Anatomie Pathologique et de Neuropathologie, Hôpital de la Timone, Marseille.
Abstract:
A retrospective study of 40 patients with various neuromuscular disorders and more than 3 muscle fibers with rimmed vacuoles has been performed. Two subgroups of patients were distinguished according to the presence or absence of inflammatory exudates. In the first group (14 patients), inflammatory exudates were observed and numerous fibers showed partial invasion. Abnormal filamentous inclusions (16-18 nm in diameter) were found by electron microscopy in muscle fibers cytoplasm and/or nuclei. The diagnosis of inclusion body myositis (IBM) was made in these cases. They presented with insidious proximal muscle weakness and were not improved by immunosuppressive therapy. Immunohistological studies demonstrated T lymphocytes predominance, only few natural killer and B lymphocytes. The number of T8 lymphocytes was high in endomysial sites while T4 were more numerous in perivascular exudates. Abnormal membranous expression of class I MHC antigens was observed on muscle fibers lying near the inflammatory exudates. In the second group of cases (26 patients), no inflammatory exudate was observed. This group of neuromuscular diseases with rimmed vacuoles was heterogeneous. In 10 cases, abnormal filamentous inclusions (16-18 nm in diameter) were observed in rimmed vacuoles. However, this ultrastructural feature did not help in distinguishing subgroups. Various neuromuscular disorders were observed in this group: oculopharyngeal muscular dystrophy (12 cases with IBM like filaments in 4 cases), chronic spinal atrophy (5 cases with IBM like filaments in 3 cases), post poliomyelitis syndrome (2 cases with IBM-like filaments in one), muscle glycogenosis with IBM like filaments (2 cases), hereditary limb girdle myopathy or distal myopathy (3 cases) and 1 patient clinically presenting with polymyositis and another with cramps and myalgias. No abnormal sarcolemmal expression of class I MHC was found in this group. The pathogenesis of IBM is discussed. Besides T cell mediated cytotoxicity, denervation may be involved. The nature of the abnormal 16-18 nm filamentous inclusions remains unknown. These filaments are not IBM specific.
Insights
This study on neuromuscular disorders found that inclusion body myositis (IBM) involves inflammatory exudates and abnormal filamentous inclusions. Other conditions with rimmed vacuoles showed heterogeneity and lacked specific diagnostic markers.
Area of Science:
- Neuromuscular Pathology
- Electron Microscopy
- Immunohistology
Context:
- Retrospective analysis of 40 patients with neuromuscular disorders and rimmed vacuoles.
- Distinguished subgroups based on presence or absence of inflammatory exudates.
Purpose:
- To investigate the characteristics and potential diagnostic markers of neuromuscular disorders with rimmed vacuoles.
- To differentiate inclusion body myositis (IBM) from other conditions presenting with rimmed vacuoles.
Summary:
- Inclusion body myositis (IBM) cases (14/40) exhibited inflammatory exudates, T-cell infiltration, and abnormal filamentous inclusions (16-18 nm).
- Non-IBM cases (26/40) with rimmed vacuoles were heterogeneous, lacking inflammatory exudates and specific diagnostic ultrastructural features.
- Abnormal filamentous inclusions were found in both IBM and some non-IBM cases, indicating they are not specific to IBM.
Impact:
- Highlights the heterogeneity of neuromuscular diseases with rimmed vacuoles.
- Suggests T-cell mediated cytotoxicity and potentially denervation in IBM pathogenesis.
- The nature and specificity of the observed filamentous inclusions remain undetermined.