Chronic progressive external ophthalmoplegia and myalgia associated with tubular aggregates

Horse lumbrical muscle: possible structural and functional reorganization in regressive muscle

An anatomical study of horse lumbrical muscle (Lm) was carried out by light and electron microscopy in combination with immunochemical and cytochemical methods. Paraffin sections were subjected to haematoxylin and eosin (H & E) and Masson's trichrome staining for morphometric analysis. Paraffin sections were also used for immunostaining by anti-PGP 9.5 for reaction with nerve-protein associated-structures, anti-heat-shock protein 70 (hsp 70) for detection of gene expression changes, anti-fast myosin for the determination of muscle fibre types, and for detection of apoptotic gene expression of muscle fibres by the TUNEL method. The distribution of muscle fibre types on frozen sections was also examined by assaying ATPase (pH 4.2). We found that the proximal end of the tendon of the unipennate-shaped Lm binds to the deep digital flexor tendon, and the distal end of the Lm tendon connects to the medial surface of the palmar annular ligament. The Lm was not always present, but when found it varied in length greatly, up to 8 cm (muscle part alone), and weighed less than 1 g. The Lm was white, pale, or reddish in colour depending on the ratio of muscle fibre and connective tissue contents. The semi-tendinized regressive Lm was composed of rich vasculature, peripheral nerves, and nerve-like organs similar to the neuromuscular spindle (NMS). The extrafusal muscle fibres (e-lm) that surround the NMS were replaced with a thick outer capsule of connective tissues (CT) in the Lm nerve-like organ, which we named the neurotendinous capsule (NTC) organ. NTC organs exist alone or as multiple structures (up to eight) surrounded by a common outer capsule at the outermost CT ring. The NTC possesses several intrafusal muscle fibres (ifm) just as the NMS does. That the ifm was associated with nerve endings was confirmed by anti-PGP 9.5 and electron microscopic observation. Some muscle fibres in ifm and e-lm reacted with anti-fast twitch myosin and with anti-hsp 70. The e-lm exhibited at least two fibre types, determined by ATPase (pH 4.2) assay. The ifm exhibited mainly type I (slow twitch) fibres. No apoptotic gene expression was detected in either ifm or e-lm, suggesting the Lm is a vital organ. The degenerating fibres observed in ifm and e-lm indicate that the turnover rate of cytoplasmic components is accelerated. We attribute this phenomenon to the necessity for adaptation to new environmental demands. The surprising finding of tubular aggregates (TAs) in ifm of the NTC organ suggests that the Lm is continuously adapting. Some results related to variation in diameter of the collagen fibrils, isolation of the NTC organ and the myofibrillar protein constituents are also discussed. In conclusion, the so-called regressive Lm has rich vasculature, many peripheral nerves, and newly described NTC organs. The induction of heat-shock protein, lack of apoptotic gene expression in ifm and e-lm fibres, and TA formation in ifm suggest that horse Lm responds to environmental stress through reorganization and/or remodelling of cell constituents. We hypothesize that the horse Lm has lost its original role as a contractile element and changed to another function, likely as a vital nerve organ.

On a dominantly inherited myopathy with tubular aggregates

A 19-year-old patient presented with exercise-related myalgia, fatigue and elevated creatine kinase levels. Histology of a muscle biopsy was characterized by the presence of very large amounts of tubular aggregates. Both his father and paternal grandfather had elevated creatine kinase and large amounts of tubular aggregates in their muscle biopsies. The aggregates consisted of closely packed vesicles and tubules filled with electron-dense material or with one to several smaller tubules. Disorders with tubular aggregates in the muscle fibres such as hyperornithinaemia with gyrate atrophy of the retina, hypokalaemic periodic paralysis, hyperkalaemic periodic paralysis, myotonia congenita, alcoholism, osteomalacic myopathy etc. have been excluded. Tubular aggregates can be found in muscle disorders characterized by exercise-induced cramps, pain and stiffness. They also represent the predominant histological feature of some familial myopathies due to a yet unidentified genetic defect. In our family, there was male-to-male transmission, confirming dominant inheritance.

Oculopharyngeal muscular dystrophy, other ocular myopathies, and progressive external ophthalmoplegia

Progressive external ophthalmoplegia comprises many different disorders. Those of childhood onset can be separated from juvenile or adult onset. Among those of later onset the most common causes are oculopharyngeal muscular dystrophy, oculopharyngodistal muscular dystrophy and the several mitochondrial disorders, especially those with large deletions of mitochondrial DNA (mtDNA) (sporadic), those with maternal inheritance (point mutations), or the autosomal dominant forms with multiple deletions of mtDNA. Ophthalmoplegia of presumably neurogenic origin is seen in some of the familial spinocerebellar ataxias. Advances in molecular genetics should provide information about affected gene products and, therefore, pathogenesis.

Palpebral ptosis and muscle fatiguability associated with perineurial cell ensheathment of muscle fibers: a new disease of the neuromuscular junction?

Perineurial cell ensheathment of muscle fibers has been reported only in one patient. Here we describe a new case with identical morphologic features and a similar, but milder clinical course characterized by progressive muscle weakness and bilateral palpebral ptosis. EMG examination (including repetitive stimulation) and antibodies against acetylcholine receptors were normal. Muscle biopsy revealed several muscle fibers encircled by stratified rings of homogeneous material in which elongated nuclei were visible; this material was positively stained by antibodies directed at epithelial membrane antigen. On ultrastructural examination these encircling-fiber spirals had the characteristics of perineurial cells. It is not clear yet whether perineurial cell ensheathment of muscle fibers is an occasional feature, or whether it has a pathogenetic role in the clinical picture of both cases. The perineurial sheaths might alter the correct neuromuscular transmission mimicking a myasthenia-like disease, either by interfering with the neuromuscular junction, or by changing the microenvironment, and, thus, altering the general excitability of the muscle fibers.

Early-onset myopathy with tubular aggregates

We report a 14-year-old girl with early onset of slowly progressive muscular weakness and atrophy. There was no family history of neuromuscular disease. A persistent increase of serum creatine kinase was found. Muscle biopsy specimens showed type 1 fiber predominance and tubular aggregates in almost every fiber. The clinical findings and pathology suggest that the disease represents one variant in a group of rare myopathies with different patterns of inheritance, characterized by slowly progressive muscle weakness and tubular aggregates.