Excessive intracellular acidosis of skeletal muscle on exercise in a patient with a post-viral exhaustion/fatigue syndrome. A 31P nuclear magnetic resonance study

Postviral fatigue syndrome: time for a new approach

Controversial views on the postviral fatigue syndrome ("myalgic encephalomyelitis") were critically appraised in their historical context and recent advances in research (virology, immunology, neurophysiology, histopathology, and epidemiology) reviewed. Flaws detected in certain aspects of recent research included in particular failure to define fatigue, inadequate assessment of psychological features, and absent or inappropriate control groups. The findings suggest that the fruitless dichotomy of "organic versus functional" should be replaced by a multifactorial approach. Most important, epidemiological studies with explicit operational case definition are essential before progress can be made in the management of this distressing disorder.

Hypotheses of peripheral and central mechanisms underlying occupational muscle pain and injury

In an overview of the problem of occupational muscle pain the evidence indicates that injury is more common the greater the load and the worse the posture in which the work is performed. The commonest are backstrains or ligament or joint damage due to overuse. Fatigue is associated with alterations in energy metabolites in muscle while pain is often due to microscopical damage to the cellular architecture. The progress of pathological changes in muscle following occupational injury may be similar to those seen in primary fibromyalgia (fibrositis) because of a final common pathway involving calcium-induced secondary damage. Occupational muscle pain frequently occurs in the muscles supporting the upper limb girdle and head in workers engaged in repetitively performing skilled manipulations or activities requiring high or sustained mental concentration. It is suggested that both occupational myalgia of this kind may be due to an imbalance in the use of muscles for postural activity (holding or supporting fine movements) compared to phasic use in dynamic work. While there are undoubtedly muscular indications of damage these may be secondary to alterations in (unconscious) central motor control mechanisms.

An unusual metabolic myopathy: a malate-aspartate shuttle defect

Studies on a 27-year-old man with a 3-year history of exercise-induced muscle pain, passage of red urine and elevated serum creatine kinase are described. Histological examination of a biopsy from quadriceps revealed non-specific myopathic changes with occasional clusters of subsarcolemmal mitochondria. The phosphorylase stain was normal. Phosphorous nuclear magnetic resonance (NMR) spectroscopy studies of gastrocnemius and flexor digitorum superficialis muscles showed no abnormalities at rest. During aerobic exercise there was an abnormally rapid decrease in phosphocreatine concentration but the pH remained within the normal range. There was a build-up of phosphomonoester (probably glucose 6-phosphate), usually indicative of a block in glycolysis. However, a primary defect in the glycolytic pathway seemed unlikely because muscle acidified normally during ischaemic exercise. Recovery from exercise was unusual in that phosphocreatine resynthesis and inorganic phosphate disappearance followed similar prolonged time courses (in control subjects the rate of inorganic phosphate disappearance was about twice as fast as the rate of phosphocreatine resynthesis). The transport of inorganic phosphate into the mitochondria appeared to be delayed. These slow recovery data suggested that oxidative metabolism was impaired. However, with all substrates tested, isolated muscle mitochondria had rates of oxygen uptake that were similar to control values, thereby ruling out a primary defect in mitochondrial respiration. A system involving several mitochondrial transport systems, the malate-aspartate shuttle, was measured. The activity in the patient's isolated mitochondria was less than 20% of the activity present in samples from control subjects. This patient is the only one so far reported with a defect involving the malate-aspartate shuttle system.

NMR as a metabolic tool

We have briefly reviewed the broad range of applications of NMR spectroscopy to metabolism in tissues and biological fluids. Most of these studies are in the exploratory stage, though the potential of NMR for non-invasive and non-destructive monitoring of certain important substrates and reaction pathways is considerable. The limitations of the technique lie in its relative insensitivity and the rather restricted range of substances that it can detect, as well as the current expense. So far, the main clinically useful applications have been in the diagnosis and monitoring of treatment of certain inborn errors of metabolism, namely those that result in altered energy of pH states or the abnormal accumulation of significant amounts of metabolites in body fluids. It might be expected that as localization techniques improve, clinically useful information will be obtained in a wide range of ischaemic or hypoxic states, e.g. stroke and myocardial infarction. The possibility of producing a detailed spatial image of metabolite concentrations (e.g. ATP), in the way that NMR imaging techniques currently do using features of the water proton resonance, is attractive and the initial results are very encouraging (Bogusky et al, 1986; Bailes et al, 1987; Blackledge et al, 1987).

Virus infection and knee injury

Serological evidence of virus infection was sought in 31 consecutive patients presenting with knee swelling and compared with age/sex-matched controls. In a normal age/sex-matched control group, 42% of patients had evidence of recent or past infection with Coxsackie B virus, emphasising the care required in the evaluation of the significance of Coxsackie B neutralization titres in individual patients. Of 12 patients presenting with knee swelling and a history of a twisting injury, eight had serological evidence of recent or past infection with Coxsackie B virus, and one had evidence of a current adenovirus infection.

Chronic fatigue and myalgia syndrome: mitochondrial and glycolytic studies in skeletal muscle

Clinical and biochemical findings in skeletal muscle in 11 patients with chronic fatigue myalgia syndromes of unknown aetiology are reported. All patients had severe asthenia for from one to 10 years with greatly limited exercise capacity and protracted exhaustion after minor exercise. Diffuse myalgia was prominent and was exacerbated for hours to days after exercise. Assay of skeletal muscle carnitine, phosphorylase, all glycolytic enzymes and the mitochondrial marker enzymes monoamine oxidase, isocitrate dehydrogenase and cytochrome oxidase were normal. These findings lend no support to the presence of a major defect in muscle intermediary energy pathways in this syndrome.

An evaluation of the effect of fasting on the exercise-induced changes in pH and Pi/PCr from skeletal muscle

The changes in the response of skeletal muscle to maximal dynamic exercise were investigated in going from a fasted state to a refed state by means of 31P NMR spectroscopy. It was found that in the fasted state, exercise-induced changes in Pi/PCr and in pH were both inhibited, in comparison with those in the refed state.

Current issues concerning management of the fibrositis/fibromyalgia syndrome

The fibrositis/fibromyalgia syndrome is one of the commonest forms of musculoskeletal pain seen in clinical practice. It is diagnosed on the basis of widespread pain accompanied by the physical finding of multiple tender points in remarkably reproducible locations. Accompanying the pain are two symptoms commonly associated with the "systemic" rheumatic disorders, namely morning stiffness and easy fatigability. Unlike the classical rheumatic diseases, however, fibrositis is not responsive to anti-inflammatory medications, including corticosteroids. Current therapeutic strategies, which are only partly successful, are aimed at modifying those factors that seemingly influence the severity and course of the condition; such afferent features include sleep disturbance, overuse syndromes, mechanical stress, psychic stress, and other causes of chronic pain. Major unresolved issues center around the assessment of functional disability in fibrositis and the apparent relationship to trauma in some patients. Until more is known about the underlying pathogenesis of this common condition, significant progress will be thwarted.

Potential of NMR and PET for determining tumor metabolism

The basic principles underlying nuclear magnetic resonance spectroscopy (MRS) and positron emission tomography (PET) are explained. Examples of work relating to tumor metabolism are given and some of the important findings of clinical interest are presented. The future prospects of both systems are explored.

Viral illnesses and sports performance

Viruses are ubiquitous and cause numerous infections in humans. These may vary from asymptomatic infection to severe debilitating illness. Viruses enter the host cells to replicate, using host synthetic mechanisms, and, thus, are resistant to conventional antibiotics. The human body responds to viral infection by synthesising specific antibody which can be used to aid diagnosis. Infectious mononucleosis (glandular fever) commonly affects the 15 to 30 years age group. It may produce severe debility which may last a month or more. Coxsackie virus infection can produce symptoms of the common cold but may also invade heart muscle and produce myocarditis, a potentially serious disease. Other viruses also produce a wide spectrum of disease. Recent evidence has shown that people undergoing severe mental or physical stress may have reduced immunity to viral infections. There are risks associated with strenuous physical activity during the acute phase of viral infection, and there are reports of sudden death and serious complications occurring in previously fit young adults who undertake vigorous exercise when in the acute phase of a viral illness. Abnormalities of skeletal muscle have been demonstrated in patients with viral infection and this may explain the loss of performance experienced by athletes after upper respiratory tract infection. As a general rule, for all but mild common colds, it is advised that the athlete avoids hard training for the first month after infection.

Phosphocreatine content and intracellular pH of calf muscle measured by phosphorus NMR spectroscopy in occlusive arterial disease of the legs

Energy metabolism of calf muscle was assessed non-invasively by phosphorus (31P) NMR spectroscopy in eleven patients with symptomatic arterial occlusion and in seven matched controls. Phosphocreatine (PCr) content and pH values decreased during non-ischaemic foot exercise to lower values in severely afflicted patients but in all patients, as a group, they were not significantly decreased compared to controls. In contrast, recovery from ischaemic exercise (arterial occlusion by a tourniquet) demonstrated significant differences between patients and controls. Intracellular pH and PCr recovered more slowly in patients than in controls; PCr recovery proceeded exponentially with a recovery half-time of 203 +/- 74 s in patients compared to 36.7 +/- 5.5 s in controls (P less than 0.02). Phosphocreatine (PCr) recovery after ischaemic exercise correlated significantly with the degree of arterial stenoses as assessed by Doppler ultrasound (r = 0.739, P = 0.019) and by angiography (r = 0.885, P = 0.005), suggesting that the degree of large vessel stenoses limits the postischaemic increase in mitochondrial oxidative phosphorylation. Reactive blood flow after ischaemia failed to correlate with PCr recovery or with the degree of arterial stenoses. Phosphorus (31P) NMR spectroscopy provides, therefore, quantitative parameters of muscle energy metabolism in patients with peripheral arterial occlusions.

Electrophysiological studies in the post-viral fatigue syndrome

Single fibre electromyography (SFEMG) was studied in 40 patients with the post-viral fatigue syndrome. These patients were also assessed clinically, serologically, virologically and immunologically. About 75% of the patients had definitely abnormal SFEMG results. This was regarded as evidence of abnormality in the peripheral part of the motor unit. The muscle fibre was the likely site of involvement.

The postviral fatigue syndrome--an analysis of the findings in 50 cases

The clinical, pathological, electrophysiological, immunological and virological abnormalities in 50 patients with the postviral fatigue syndrome are recorded. These findings confirm the organic nature of the disease. A metabolic disorder, caused by persistent virus infection and associated with defective immunoregulation, is suggested as the pathogenetic mechanism.

Inflammatory myopathies: Part 1

The inflammatory myopathies have diverse clinical and pathological features and multiple etiologies. Some are confined to a single muscle or group of muscles (e.g., orbital myositis and localized nodular myositis) while others are diffuse. Infective forms may be due to viral, bacterial, fungal, protozoal, or parasitic organisms. Viruses may cause acute self-limited forms of myositis and have been isolated from muscle in some cases of acute rhabdomyolysis and inclusion body myositis. They have also been implicated in some cases of congenital myopathy and in polymyositis and dermatomyositis, but there is no evidence of viral invasion of muscle in these conditions. In polymyositis and dermatomyositis there are derangements in humoral and cellular immune function, and recent evidence suggests an underlying disturbance of immunoregulation. The roles of genetic factors, drugs, and Toxoplasma infection have been under scrutiny. There is increasing recognition of immunological and pathological differences in polymyositis and juvenile and adult dermatomyositis, and in cases with associated connective tissue diseases, suggesting different underlying pathogenetic mechanisms. Inclusion body myositis, eosinophilic myositis, and granulomatous myositis can be separated from the other idiopathic inflammatory myopathies because of distinctive clinical and pathological features and this may also reflect different mechanisms of muscle injury. Recent developments in the treatment of the idiopathic inflammatory myopathies include the use of plasmapheresis and total-body irradiation in cases that are resistant to corticosteroids and immunosuppressive drugs.

The role of magnetic resonance spectroscopy in clinical medicine

This article presents a view which emphasises the particular perspective of a clinician who has close involvement in magnetic resonance spectroscopy (MRS) and is directed towards readers who wish to understand the likely role of MRS in clinical medicine. Many more complete reviews already exist, including two review articles from our group. Another review would hardly be justifiable and those readers seeking such an article should consult Refs. 1-5. This will be more in the nature of a personal overview of the topic and one which will touch upon some of the problems which accrue from the interactions of scientists with little appreciation of clinical medicine with clinicians who have little understanding of the complexities of the NMR experiment. Moreover, the discussion will be confined to situations where MRS is likely to impinge directly on problems of day-to-day clinical management, as opposed to situations where the results of MRS research lead to an improved understanding of particular disease states, but where there is no need for each and every patient who is a potential benificiary of the technique to undergo an MRS examination.