Quantitative histopathology of the inflammatory myopathies.

This study quantitatively assessed skeletal muscle histopathology in 57 patients with inflammatory myopathy, including 20 patients with polymyositis (PM), 19 patients with dermatomyositis (DM), and 18 patients with evidence of an additional connective-tissue disease. No histologic criteria for invariably distinguishing patients with inflammatory myopathy were established because of overlap in individual measurements, but general histopathologic distinctions were confirmed. In PM, endomysial mononuclear cell infiltration (fibers bordering on inflammation) was usual, whereas in DM inflammation of large vessels, fibers with circumscribed areas of myofibrillar loss, and perifascicular atrophy were seen. Patients with evidence of an additional connective-tissue disease were most similar to the DM patients, with a greater prevalence of perivascular inflammation than in the PM patients. Because of varying histopathology (and presumed varying pathogenesis), future therapeutic trials would be more informative if they were designed using patients with homogeneous histologic features.

Spectrum of inclusion body myositis.

The clinical, laboratory, and biopsy features are described for a large group of patients with inclusion body myositis (IBM) (15 men and four women; mean age, 63 years). A quantitative histopathologic analysis of muscle biopsy specimens revealed less fiber necrosis and endomysial and perivascular inflammation in IBM than in polymyositis (PM) and dermatomyositis, but a more frequent occurrence of dark-angular and hypertrophied fibers. Rimmed vacuoles were present in 3.4% of all fibers and 15- to 18-nm filaments were identified in the biopsy specimens of nine of 11 patients. A panel of monoclonal antibodies immunoreactive with lymphocytes and cells of monocyte/macrophage lineage suggested that the inflammatory reaction in IBM was similar to that in PM (but not dermatomyositis) and mediated by cellular immune responses. These studies confirm the clinical and histopathologic distinctions between IBM and chronic PM, and that differentiation between these disorders is often difficult.

Muscle denervation in peripheral arterial disease.

Muscle function is often severely impaired in peripheral arterial disease (PAD), but the effects of repeated ischemic events upon nerve and muscle are incompletely characterized. We performed comprehensive electrophysiologic studies and skeletal muscle histologic analysis in six patients with unilateral PAD and five control subjects matched for age and activity level. In the PAD patients, all ischemic legs showed both electrophysiologic and histologic evidence of chronic partial denervation-reinnervation restricted to distal muscles. Two of the PAD patients had evidence of milder distal denervation in the nonischemic legs. Two of the controls had denervation in at least one leg, but in each case electrophysiologic findings were pathognomonic of L-5 and S-1 radiculopathies. All other control legs and nonischemic legs were normal. These results suggest that recurrent ischemia associated with PAD may cause muscle denervation, which may be one of the mechanisms responsible for decreased exercise performance in these patients.

Diabetic muscle infarction: a new perspective on pathogenesis and management.

Two patients with insulin dependent diabetes mellitus developed recurrent episodes of focal muscle pain and swelling. Clinical evaluation, magnetic resonance imaging (MRI) and muscle biopsy confirmed the diagnosis of recurrent hemorrhagic muscle infarctions. Our studies suggest that muscle infarction occurred because of hypercoagulability and associated vascular endothelial damage. Based on these findings we recommend long-term anticoagulation to prevent recurrent infarction.

Effect of exercise training on skeletal muscle histology and metabolism in peripheral arterial disease.

Patients with symptomatic peripheral arterial occlusive disease have a claudication-limited peak exercise performance that is improved with exercise training. The effects of training on skeletal muscle metabolism were evaluated in 26 patients with claudication, randomized into a 12-wk program of treadmill training (enhances muscle metabolic activity in normal subjects), strength training (stimulates muscle hypertrophy in normal subjects), or a nonexercising control group. Gastrocnemius muscle biopsies were performed at rest and before and after training. After 12 wk, only treadmill training improved peak exercise performance and peak oxygen consumption. Treadmill training did not alter type I or type II fiber area and did not increase citrate synthase activity but was associated with an increase in the percentage of denervated fibers (from 7.6 +/- 5.4 to 15.6 +/- 7.5%, P < 0.05). Improvement in exercise performance with treadmill training was associated with a correlative decrease in the plasma (r = -0.67) and muscle (r = -0.59) short-chain acylcarnitine concentrations (intermediates of oxidative metabolism). Patients in the strength and control groups had no changes in muscle histology or carnitine metabolism, but strength-trained subjects had a decrease in citrate synthase activity. Thus treadmill training increased peak exercise performance, but this benefit was associated with skeletal muscle denervation and the absence of a "classic" mitochondrial training response (increase in citrate synthase activity). The present study confirms the relationship between skeletal muscle acylcarnitine content and function in peripheral arterial occlusive disease, demonstrating that the response to treadmill training was associated with parallel improvements in intermediary metabolism.

Histochemistry of mouse extraocular muscle.

The organization, histochemical and endplate characteristics, and percentage fiber composition are described for mouse extraocular muscle (EOM). Both recti and obliques, but not the retractor bulbi, have two concentric layers, an inner global and superficial orbital. Three histochemical fiber types, coarse, fine and granular, are present in the EOM. The intermediate diameter coarse fibers are focally innervated and occur in both layers in all muscles. The large diameter granular fibers are focally innervated and occur in all EOM in the global layer. The small diameter fine fibers have multiterminal endplates and occur in both layers of the recti. Fine fibers are not seen in the obliques or retractor bulbi. Focal endplates are confined to a broad diagonal band across the middle one third of the muscle, whereas multiterminal endplates are scattered throughout the length of the muscle.

Structure and histochemistry of human extraocular muscle.

Human extraocular muscles are arranged in overlapping, concentric zones of fascicles separated by a relatively thick layer of perimysial connective tissue. Three morphologically distinct fiber types are evident: coarse and granular fibers are similar to the type I and II fibers found in limb skeletal muscle, but fine fibers are unique to EOM. The histochemical staining pattern of the three fiber types is reflected in the fine structural features of the fibers, particularly for the size and distribution of mitochondria. EOM fibers have a rich endowment of mitochondria compared with limb skeletal fibers. Limb muscle biopsy combined with histochemistry has proven to be a useful tool in differentiating neurogenic and myopathic disorders and in diagnosing most neuromuscular disorders. In contrast, EOM biopsy and histochemistry have not yet proven to be useful in distinguishing myopathic from neurogenic disorders. Extraocular muscles normally have many of the features associated with myopathies of limb muscle including an increase in endomysial connective tissue, variation in fiber size, and the presence of both central nuclei and ragged-red fibers. Biopsies from patients with chronic progressive external ophthalmoplegia display an increased occurrence of these same features, but never the type grouping or group atrophy associated with neurogenic disorders of limb muscle. A further understanding of the pathogenesis of disorders of ocular motility may have to await the application of specific antibodies which readily identify proteins associated with specific myopathies or denervated fibers.

Mitochondrial morphometrics of histochemically identified human extraocular muscle fibers.

Three fiber types--coarse, granular, and fine--were readily identified in histochemical cryostat sections of human extraocular muscle (EOM). The cryostat retrieval method was utilized to identify these three fiber types in serial electron microscopic thin sections. Using morphometric techniques, five mitochondrial variables (mitochondrial volume fraction, mitochondrial profile size, mitochondrial profile density, and clusters of two or of three or more mitochondrial profiles) were determined for a total of 162 histochemically identified fibers from two regions (orbital and global zones) from six EOMs. Coarse fibers had numerous large-sized mitochondrial profiles, often occurring in clusters. Granular fibers had fewer and smaller-sized profiles scattered across the fiber. Fine fibers had the most numerous, but smallest-sized mitochondrial profiles. Despite significant differences in group (fiber types) means for the mitochondrial variables, no single variable was sufficient for separating fiber types into distinct populations. Although a scattergram plot of two variables was sufficient to separate orbital zone fibers, a computer-generated, multivariate discriminant analysis was needed to separate the global zone fibers into distinct populations. These results will aid future studies on normal and pathological human EOM by providing a morphometric basis for identifying fiber types in the orbital and global zones.

Distribution of capillaries in normal and diseased human skeletal muscle.

The distribution of capillaries was studied in muscle biopsies in a large number of normal subjects and in patients with disuse atrophy, inflammatory myopathies, and other chronic myopathic and neurogenic disorders. The cryostat retrieval technique was used, along with capillary and muscle fiber morphometry, to quantitate capillary distribution around specific fiber types. In all diseased and normal muscle, the number of capillaries per fiber (C/F) and the number of capillaries surrounding a fiber (CAF) increased with fiber diameter. More capillaries typically surrounded type 1 than type 2 fibers within a given group. When all inflammatory myopathy patients (polymyositis, dermatomyositis, and polymyositis plus second connective tissue disease) were compared with normal adults, their muscle biopsies had fewer capillaries per fiber over the same diameter range. The numerous variables influencing capillary number in normal and diseased muscle are discussed.

Morphogenesis of motor endplates along the proximodistal axis of the mouse hindlimb.

The morphogenesis of motor endplates along the proximodistal hindlimb axis is described for the mouse using nonspecific cholinesterase histochemistry and electron microscopy. There is a two day lag in relative stages of development between a proximal muscle (rectus femoris, RF) and a distal muscle (flexor hallucis brevis, FHB). Cholinesterase activity first appears in the RF on embryonic day 15 and the FHB on embryonic day 17. In the following days, faint wisps of reaction product thicken, form small ovals on myotubes, and finally enlarge with internal ramifications as the muscle fibers increase in diameter. Axons first enter the RF between embryonic days 12 and 13, and contact both embryonic cells (most likely myoblasts) and cells assumed to be Schwann cells. Myotubes are present in the RF the following day. The first signs of synapse formation-appearance of symmetrical electron opaque membrane patches, and dense cored and synaptic vesicles--occur between axons and myotubes in the RF on embryonic day 15. During the following days basal lamina material accumulates in the synaptic cleft, coated vesicles and postjunctional folds appear in the myotubes, and synaptic vesicles accumulate in the axon terminals. By postnatal day 42 the axon terminals lay in primary gutters opposite deep secondary postjunctional folds, and are separated and capped by Schwann cell processes.

Structure, innervation, and age-associated changes of mouse forearm muscles.

In spite of a decline in muscle strength with age, the cause of the overall decrease in motor performance in aged mammals, including rodents, is incompletely understood. To add clarity, the gross organization, innervation, histochemical fiber types, and age-associated changes are described for mouse forearm muscles used in a variety of motor functions. The anterior (flexor) and posterior (extensor) forearm compartments have the same arrangement of muscles and gross pattern of innervation as the rat. Two primary histochemical fiber types, fast/oxidative/glycolytic (FOG) and fast/glycolytic (FG), with characteristic histochemical staining patterns were observed in all forearm muscles. Additionally, there was a small population of slow/oxidative (SO) fibers confined to the deep region of a single muscle, the flexor carpi ulnaris (FCU). Between 18 and 26 months the FCU muscle displayed fibers with morphological features distinct from earlier ages. Fibers displayed a greater variation in size, a loss of their uniform polygonal shape, and a dramatic increase in clumps of subsarcolemmal mitochondria, lysosomes, and lipofuscin granules. Many of the fibers had a distinctly atrophic, angular shape consistent with recent denervation. Morphometric analyses of the FCU's source of innervation, the ulnar nerve and one of its ventral roots (C8), were consistent with the denervation-like changes in the muscle fibers. Although, there was no net loss of myelinated axons between 4 and 26 months of age, there was a significant increase in the density of degenerating cells in both the ulnar nerve and ventral root C8.

Effects of selective and nonselective beta-adrenergic blockade on mechanisms of exercise conditioning.

Exercise conditioning involves adaptations in the heart, peripheral circulation, and trained skeletal muscle that result in improved exercise capacity. Since the specific influence of beta-adrenergic stimulation on these various adaptations has not been clear, we studied the effect of beta 1-selective and nonselective beta-adrenergic blockade on the exercise conditioning response of 24 healthy, sedentary men after an intensive 6 week aerobic training program. Subjects randomly assigned to receive placebo, 50 mg bid atenolol, or 40 mg bid nadolol were tested before and after training both on and off drugs. Comparable reductions in maximal exercise heart rate occurred with atenolol and nadolol, indicating equivalent beta 1-adrenergic blockade. Vascular beta 2-adrenergic selectivity was maintained with atenolol as determined by calf plethysmography during intravenous infusion of epinephrine. All subjects trained at greater than 85% of maximal heart rate and 80% of VO2 max determined on drug. VO2 max increased after training 16 +/- 2% (p less than .05) in the placebo group and 6 +/- 2% (p less than .05) in the atenolol group, while there was no change in the nadolol group. At maximal exercise, subjects receiving placebo increased their exercise duration and oxygen pulse significantly greater than those receiving atenolol or nadolol. During submaximal exercise there were reductions in heart rate and heart rate-blood pressure product in all three groups, but these reductions were greater with placebo than with either drug. Leg blood flow during submaximal exercise decreased 24 +/- 2% (p less than .01) in the placebo group but was unchanged in the atenolol and nadolol groups. Lactates in arterialized blood during submaximal exercise were reduced equivalently in all three groups after training. Capillary/fiber ratio in vastus lateralis muscle biopsy specimens increased 31 +/- 6% in the placebo group and 21 +/- 6% in the atenolol group (both p less than .05) and tended to increase in the nadolol group. Succinic dehydrogenase and cytochrome oxidase activities in muscle biopsy specimens increased equivalently in all three groups, especially during submaximal exercise, these changes were less marked than that with placebo. While beta-adrenergic blockade attenuated the exercise conditioning response, skeletal muscle adaptations including increases in oxidative enzymes, capillary supply, and decreases in exercise blood lactates were unaffected. Cardiac and peripheral vascular adaptations do appear to be affected by beta-adrenergic blockade during training. Cardioselectivity does not seem to be important in modifying these effects.

Chronic changes in skeletal muscle histology and function in peripheral arterial disease.

BACKGROUND: Peripheral arterial disease (PAD) is associated with an impairment in exercise performance and muscle function that is not fully explained by the reduced leg blood flow during exercise. This study characterized the effects of PAD on muscle function, histology, and metabolism. METHODS AND RESULTS: Twenty-six patients with PAD and six age-matched control subjects were studied. Ten of the PAD patients had unilateral disease, which permitted paired comparisons between their diseased and nonsymptomatic legs. All PAD patients had a lower peak treadmill walking time and peak oxygen consumption than controls. Vascular disease (diseased leg in unilateral patients and the most severely diseased leg in bilateral patients) was associated with decreased calf muscle strength compared with control values. In patients with unilateral disease, the diseased legs had a greater percentage of angular fibers (indicating chronic denervation) and a decreased type II fiber cross-sectional area (expressed as percent of total fiber area) compared with the nonsymptomatic, or control, legs. In diseased legs, gastrocnemius muscle strength was correlated with the total calf cross-sectional area (r = 0.78, p < 0.05) and type II fiber cross-sectional area (r = 0.63, p < 0.05). Activities of citrate synthase, phosphofructokinase, and lactate dehydrogenase in all 26 PAD patients (most diseased leg) did not differ from control values. Despite a wide range in citrate synthase activity in PAD patients, activity of this enzyme was not correlated with muscle strength or treadmill exercise performance. CONCLUSIONS: In patients with PAD, gastrocnemius muscle weakness is associated with muscle fiber denervation and a decreased type II fiber cross-sectional area. In contrast, the PAD patients displayed substantial heterogeneity in muscle enzyme activities that was not associated with exercise performance. Denervation and type II fiber atrophy may contribute to the muscle dysfunction in patients with PAD and further confirm that the pathophysiology of chronic PAD extends beyond arterial obstruction.