Virus-like structures in muscle in chronic polymyositis

Inclusion body myositis in French patients. A clinicopathological evaluation

In order to establish the frequency of inclusion body myositis (IBM) in a European neuropathological unit and to evaluate the specificity of IBM pathology, we reviewed the 850 muscle biopsies performed in our laboratory over the past 7 years. Clinical histopathological and ultrastructural evaluation of all cases showing rimmed vacuoles, a constant histopathological feature of IBM, was done and the diagnosis of IBM was assessed using the clinico-pathological criteria of Calabrese, Mitsumoto & Chou (1987). Among the nine cases showing rimmed vacuoles, five were classified as IBM (group 1), either definite (3/5) or probable (2/5), and four suffered from a chronic denervating process of muscle (group 2). The overall frequency of IBM (0.6% of all muscle biopsies) was similar to that reported by North American authors. IBM represented 16% of adult idiopathic inflammatory myopathies investigated in our laboratory. Clinical and histopathological findings in group 1 were homogeneous and distinctive. Muscle biopsy was consistent with an inflammatory myopathy in all patients in group 1 and with a non-inflammatory denervating process in 3/4 patients in group 2. Typical intrasarcoplasmic inclusions were detected by electron microscopy in 3/5 cases in group 1 and 1/4 in group 2, which raises questions about the specificity of the 16-18 nm tubulofilaments. Failure to demonstrate inclusions in two patients with otherwise typical IBM, was probably related to the paucity of rimmed vacuoles observed in these cases.

Recent advances in the morphology of myositis

Myositis in man may be divided into infectious and non-infectious forms. The myopathologist more often deals with the latter forms which comprise dermatomyositis/polymyositis, inclusion body myositis, mixed connective tissue disease/collagenoses, and granulomatous myopathies. Modern morphological techniques as enzyme-histochemistry, electron microscopy, immunohistology, and morphometry are of different value in various forms of myositis, but are often indispensable techniques in up-to-date diagnostic work up of a myositis.

Comparative study of alterations of skeletal muscle in Duchenne muscular dystrophy and polymyositis

Histological and ultrastructural alterations of skeletal muscles in Duchenne muscular dystrophy (DMD) (32 cases) and polymyositis (PM) (33 cases) were compared qualitatively and quantitatively. Regeneration is more numerous in PM than DMD throughout all stages. Stromal fibrosis and hyaline fiber with delta lesion are characteristic for DMD. In the electron microscope, we observed the usual preservation of basement membrane in degenerating muscle fibers and uncomplicated muscle regeneration in PM. On the other hand, there were partial disruption of the plasma membrane lining the delta lesion and degeneration of basement membrane and probable invasion of collagen fiber into sarcoplasm in some hypercontracted fibers in DMD. Besides, there appeared atypical form of regeneration in DMD, namely myocytes arrested at the stage of mononuclear myoblast or primitive myotube with degeneration of myofibrils and cytoplasmic organelles. At the advanced stage of DMD, there was scarce activity of regeneration. Stromal fibrosis, abnormality of membrane systems, and failure of regeneration were the characteristics of DMD.

Inflammatory myopathy: a review of etiologic and pathogenetic factors

Human idiopathic inflammatory myopathy is an acquired disorder with an annual incidence of two to five cases per million. A genetic influence on host susceptibility may also play a role. With the marked heterogeneity of the disease one of the major challenges is to identify subsets that might share a more uniform pathogenesis and manifest a less diverse profile of clinical findings, histopathological abnormalities, and natural history. Dermatomyositis can be distinguished by clinical appearance and pathological changes, but the recognition of additional disease subsets remains very inexact. Current evidence suggests that dermatomyositis occurs as a result of a vasculopathy, but immune mechanisms involved in other categories of idiopathic inflammatory myopathy may also involve cell-mediated immunity and possibly multiple mechanisms. Even though viral-induced muscle inflammation occurs in humans, there is no convincing evidence for a viral cause of idiopathic inflammatory myopathy. Experimental allergic myositis may be produced by the injection of animals with skeletal muscle homogenates and complete Freund's adjuvant, but the myositogenic factor is unknown and the parallels between experimental allergic myositis and human idiopathic inflammatory myopathy are limited.

Chloroquine-induced cytosomes with curvilinear profiles in muscle

A patient with systemic lupus erythematosus (SLE) was treated with chloroquine therapy for four years after the onset of her illness. Nine years after cessation of chloroquine, muscle weakness developed as part of the SLE. Four muscle biopsies performed for diagnostic purposes revealed varying degrees of inflammatory change as well as distinctive cytosomes with curvilinear profiles (CCPs). These CCPs were identical to those reported in Batten disease, a degenerative disorder of children which has a clinical course different from SLE. The CCPs seen in this case of SLE are thought to result from the effect of chloroquine on membrane systems within muscle cells. This report calls attention to the fact that CCPs are not unique to Batten disease bu may also occur in muscle of SLE patients treated with chloroquine.

Acute viral polymyositis with predominant diaphragm involvement

A 20-month-old mentally retarded girl developed an acute upper respiratory infection, followed by breathing difficulties, leading to death. Picorna virus-like particles were demonstrated in a mildly affected quadriceps femoris muscle biopsy, while the necropsy findings demonstrated an acute polymyositis with predominant diaphragm involvement. The mental retardation was due to micropolygyria of the brain. Initial respiratory difficulties are an unknown feature of polymyositis. In this case the upper respiratory infection, possibly caused by a Coxsackie B2, is evoked as responsible for this unusual distribution of the acute viral polymyositis.

Antibody levels to parainfluenza, rubella, measles, and influenza A virus in children with polymyositis

The CF and HI antibody titers to rubella and measles viruses, the CF titers to influenxa A, and the HI titers to parainfluenza 1, 2, and 3 were carried out on the sera of 20 patients with childhood polymyositis and their matched controls. The titers for measles, parainfluenxa 1, and influenza A were slightly higher for patients than for controls. The control group had antibody titers to rubella and parainfluenza 2 and 3 higher than or similar to those of patients. Strong patterns or significant differences for a given virus or virus group were not encountered.