Muscle biopsy

The authors suggested that this patient had a defect in lipid metabolism, based on the muscle biopsy. Muscle mitochondria are a principle site for beta-oxidation of fatty acids. Microvesicular steatosis can progress to liver failure with severe and prolonged impairment of beta-oxidation. This metabolic defect may have exacerbated the direct toxic effects of cocaine. 

An interesting hypermetabolic myopathy was discovered and biochemically explored by Luft et al. (L7). There was no evidence of hyperthyroidism, and mitochondria from biopsied muscle had a high rate of respiration and a loosely coupled state of oxidative phosphorylation. A few other cases of unusual myopathies with loosely coupled mitochondria have since been described (e.g., S12), although it does not seem that this is a single disease entity. 

Sugita, H., Okimoto, K., and Ebashi, S., Some observations on the microsome fraction of biopsied muscle from patients with progressive muscular dystrophy. Proc. Jap. Acad. 42, 295-298 (1966). 

The low-affinity fast channel syndrome is a rare, recessive condition where patients generally present with moderately severe myasthenic symptoms from birth (Uchitel et al 1993, Ohno et al 1996). Electrophysiologic studies revealed decremental CMAP and very small MEPPs. Single channel recordings from biopsied muscle endplate showed infrequent, abnormally brief openings in response to ACh. Morphologic studies demonstrated normal end plate structure, with normal number of AChR and no evidence of myopathy. 

Caffeine is a strong activator of CICR it sensitizes RyR to activating Ca2+ and increases the maximum attainable level. Because high concentrations (>mM) of caffeine effectively discharge Ca2+ from the Ca2+ store, it is frequently used for experimental evaluation of functional occurrence of RyRs. Caffeine is used for diagnosis of MH muscles biopsied from MH patients contract by a lower dose of caffeine than normal human, due to an enhanced CICR activity (see Disease)./Para>... 

Figure 9. One-legged exercise studies showing the muscle glycogen content of the exercised (—) and rested legs (—) in two subjects. A. Muscle biopsy samples were obtained immediately after exercise (a) and during three days when fed a carbohydrate-rich diet (a). B and C. The diet was total starvation (z) for two days following exercise (B) or carbohydrate-poor (o) for three days following exercise (C). This was followed by a second one-leg exercise bout (T) and a carbohydrate-rich diet ). Redrawn from Bergstrom and Hultman (1966) in panel A, and from Hultman and Bergstrom (1967) in panels B and C.

Figure 1. Immunofluorescent labeling of dystrophin in the Xp21 muscular dystrophies. In normal muscle, clear uniform labeling is present at the membrane of each muscle fiber. In Becker muscular dystrophy (BMD), there is inter- and intrafiber variation in labeling intensity. In Duchenne muscular dystrophy (DMD), most fibers are devoid of labeling (note, however, that in most biopsies occasional fibers exhibit weak labeling). In the biopsy from a manifesting carrier, some fibers show normal labeling and others are negative. In the former, the normal X-chromosome is active while in the latter the abnormal X-chromosome is active.

Figure 2. Erb s illustration of the pathology of muscle from patients with Duchenne muscular dystrophy. Note the variation in muscle fiber diameter, fiber-splitting, deposition of fat and infiltration of connective tissue. Drawing from several biopsies produced during final decade of 19th century. 

Although clinical examination provides important clues to diagnosis of congenital myopathies, ultrastructural and histochemical examination of muscle biopsies provides the key to definitive identification. Most of the congenital myopathies... 

From the practical viewpoint it is important to be able to distinguish infants and children with this condition from less benign disorders such as the spinal muscular atrophies. Careful histochemical assessment of muscle biopsies with histographic analysis is recommended. Most biopsies from CFTD patients show type 1 fibers which are small in relation to type 2 fibers. A revised definition of CFTD states that... 

This complex consists of at least 25 separate polypeptides, seven of which are encoded by mtDNA. Its catalytic action is to transfer electrons from NADH to ubiquinone, thus replenishing NAD concentrations. Complex I deficiency has been described in myopathic syndromes, characterized by exercise intolerance and lactic acidemia. In at least some patients it has been demonstrated that the defect is tissue specific and a defect in nuclear DNA is assumed. Muscle biopsy findings in these patients are typical of those in many respiratory chain abnormalities. Instead of the even distribution of mitochondria seen in normal muscle fibers, mitochondria are seen in dense clusters, especially at the fiber periphery, giving rise to the ragged-red fiber (Figure 10). This appearance is a hallmark of many mitochondrial myopathies. 

This complex contains 11 polypeptide subunits of which only one is encoded by mtDNA. Defects of complex III are relatively uncommon and clinical presentations vary. Fatal infantile encephalomyopathies have been described in which severe neonatal lactic acidosis and hypotonia are present along with generalized amino aciduria, a Fanconi syndrome of renal insufficiency and eventual coma and death. Muscle biopsy findings may be uninformative since abnormal mitochondrial distribution is not seen, i.e., there are no ragged-red fibers. Other patients present with pure myopathy in later life and the existence of tissue-specific subunits in complex III has been suggested since one of these patients was shown to have normal complex 111 activity in lymphocytes and fibroblasts. 

Figure 17. Inflammatory cell infiltrate in a muscle biopsy from a patient with dermatomyositis note compact nature of infiltrate and perivascular location.

Muscle biopsy is usually undertaken to confirm the provisional clinical diagnosis. Because the skin lesions normally precede those in muscle, biopsies of muscle taken early may show little abnormality. Inflammatory foci may be scanty or absent and muscle fiber diameters may be normal. However typical biopsies show discrete foci of inflammatory cells, with a predominance of B-lymphocytes (see Figure 18). These cells are situated in perimysial connective tissue rather than in the en-domysium and are often also perivascular in location. Muscle fiber necrosis occurs in JDM but muscle fibers do not appear to be the primary target of the disordered immune process. Rather, it is the micro vasculature of the muscle which appears to degenerate first and muscle necrosis is preceded by capillary necrosis, detectable at the ultrastructural level. 

Muscle biopsy shows some features in common with JDM for example, perifascicular atrophy resulting from preferential involvement of peripheral muscle fibers is seen in some cases of ADM whereas it is never seen in adult PM. Since... 

ADM may evolve over several years, the extent of fiber atrophy provides an important indication of the chronicity of muscle degeneration. Acute muscle necrosis and phagocytosis give some indication as to how active the disease is at the time of biopsy. In most biopsies from ADM patients, the inflammatory cell foci are perivascular and perimysial rather than endomysial and are dominated by B-lymphocytes. The ratio of T4 lymphocytes (helper cells) to T8 lymphocytes (cytotoxic) generally indicates a predominance of the former. As in JDM, this is consistent with humoral mechanisms of cell damage, and vascular involvement is also apparent in the form of capillary endothelial cell abnormalities (tubular arrays) and duplication of basal lamina. Loss of myofibrillar ATPase from the central portions of fibers is a common prelude to muscle necrosis. 

The histopathological features of PM may be radically different from those of JDM and ADM. There is little, if any, evidence of involvement of the micro vasculature and the muscle necrosis which occurs appears to be the direct result of targeting of individual muscle fibers. In the dermatomyositis syndromes, antibody-dependent humoral mechanisms are predominant and B-lymphocytes are seen to be the most abundant cell type in almost all JDM cases and a substantial proportion of ADM cases. In contrast, most muscle biopsies from PM patients show evidence of inflammation in which TS (cytotoxic) lymphocytes predominate (Figure 20). Moreover, the distribution of inflammatory cell infiltrates tends to be different. Instead of the mainly perifascicular location of lymphocytes in JDM/ADM, there... 

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