Occult ischaemic necrosis of skeletal muscle associated with renal failure

Muscle fibre atrophy in critically ill patients is associated with the loss of myosin filaments and the presence of lysosomal enzymes and ubiquitin

Muscle wasting and weakness are common features of patients with critical illnesses, and may impair their recovery. This study examines whether cytoskeletal and contractile proteins are damaged, and which proteolytic mechanisms might be involved, in the muscle fibre atrophy or necrosis associated with the acute myopathy of critically ill patients. Ninety-eight muscle biopsies were obtained by the conchotome method from 57 critically ill patients and examined morphometrically and by immunohistochemical labelling. Sequential biopsies showed a mean reduction in fibre cross-sectional areas of 3-4% per day. More intense immunolabelling for desmin was seen in the smaller fibres of 52% of the biopsies, while immunolabelling for dystrophin, actin and myosin heavy chains was maintained. Myosin ATPase activity was weak in the smaller fibres in some biopsies, and electron microscopy showed the loss of myosin filaments in atrophic fibres. These changes suggest that loss of the filamentous structure of myosin, without degradation of the immunolabelled epitopes, leads to the collapse of the intermyofibrillar desmin network. Fibres with abnormal desmin labelling showed increased cathepsin B, lysozyme and ubiquitin immunolabelling. Nine cases showed increased immunolabelling for heat shock protein 72. The changes in desmin immunolabelling were more prevalent in patients with higher APACHE II scores on admission, but were not related to other clinical features. The results indicate that fibre atrophy is associated with myosin filament depolymerization and the presence of several proteolytic enzymes. In our study, these changes occurred in patients who were critically ill but who did not receive large doses of steroids or neuromuscular blocking agents.

Patterns of neurophysiological abnormality in prolonged critical illness

OBJECTIVE

To describe the various patterns of neurophysiological abnormalities which may complicate prolonged critical illness and identify possible aetiological factors.

DESIGN

Prospective case series of neurophysiological studies, severity of illness scores, organ failures, drug therapy and hospital outcome. Some patients also had muscle biopsies.

SETTING

General intensive care unit (ICU) in a University Hospital.

PATIENTS

Forty-four patients requiring intensive care unit stay of more than 7 days. The median age was 60 (range 27-84 years), APACHE II score 19 (range 8-33), organ failures 3 (range 1-6), and mortality was 23%.

RESULTS

Seven patients had normal neurophysiology (group I), 4 had a predominantly sensory axonal neuropathy (group II), 11 had motor syndromes characterised by markedly reduced compound muscle action potentials and sensory action potentials in the normal range (group III) and 19 had combinations of motor and sensory abnormalities (group IV). Three patients had abnormal studies but could not be classified into the above groups (group V). All patients had normal nerve conduction velocities. Electromyography revealed evidence of denervation in five patients in group III and five in group IV. There was no obvious relationship between the pattern of neurophysiological abnormality and the APACHE II score, organ failure score, the presence of sepsis or the administration of muscle relaxants and steroids. A wide range of histological abnormalities was seen in the 24 patients who had a muscle biopsy; there was no clear relationship between these changes and the neurophysiological abnormalities, although histologically normal muscle was only found in patients with normal neurophysiology. Only three of the eight patients from group III in whom muscle biopsy was performed had histological changes compatible with myopathy.

CONCLUSIONS

Neurophysiological abnormalities complicating critical illness can be broadly divided into three types -- sensory abnormalities alone, a pure motor syndrome and a mixed motor and sensory disturbance. The motor syndrome could be explained by an abnormality in the most distal portion of the motor axon, at the neuromuscular junction or the motor end plate and, in some cases, by inexcitable muscle membranes or extreme loss of muscle bulk. The mixed motor and sensory disturbance which is characteristic of 'critical illness polyneuropathy' could be explained by a combination of the pure motor syndrome and the mild sensory neuropathy. More precise identification of the various neurophysiological abnormalities and aetiological factors may lead to further insights into the causes of neuromuscular weakness in the critically ill and ultimately to measures for their prevention and treatment.

Microvascular endothelial activation in the skeletal muscles of patients with multiple organ failure

The relationship between microvascular damage and the presence of muscle fibre atrophy and necrosis has been investigated in skeletal muscle biopsies taken from 57 patients with multiple organ failure. Immunohistochemical studies showed no loss of capillaries and no luminal thrombosis, while neutrophil leucocytes were more prevalent in the patients' biopsies than in controls. Deposition of the complement membrane attack complex (C5-9MAC) in capillaries was observed in 41% of cases. Endothelial activation was suggested by an increased intensity of expression of ICAM-1, and by an increased proportion of capillaries expressing P selectin and E selectin, although this was not directly associated with neutrophil accumulation. Endothelial swelling was present in many biopsies with 38% of the biopsies having larger capillary profiles on immunohistochemical labelling for von Willebrand factor (vWF), thrombomodulin and CD34, and on Ulex europaeus agglutinin 1 binding. Endothelial swelling was confirmed by image analysis and morphometric evaluation of capillary ultrastructure, however, the capillary luminal area was not reduced as the capillaries were dilated. Increased vWF labelling was associated with C5-9MAC deposition and with fibre necrosis, but the vascular changes were not related to fibre atrophy nor to clinical indices of the severity of the patients' illness. The results suggest that microvascular damage and ischaemia may not be major factors in the pathogenesis of muscle fibre damage in multiple organ failure, but that endothelial activation is a common occurrence. The variability in the patterns of markers of endothelial activation, and the small proportion of capillaries affected, may reflect the complexity of the endothelial response to circulating or locally produced cytokines.

The clinical and biochemical features of acute renal failure due to rhabdomyolysis

Rhabdomyolysis caused 28 out of 903 (3.1%) of cases of severe acute renal failure (ARF) treated at Leeds General Infirmary over a 14-year period (1980-1993). The commonest cause of rhabdomyolysis was muscle compression, usually due to drug- or alcohol-induced coma. Other causes included fits, infection, acute limb ischemia, trauma, and heat stroke. Prognosis was relatively good, with a 78.6% survival rate and recovery of renal function to normal in all survivors who were followed up. The creatinine/urea ratio was higher in ARF due to rhabdomyolysis than in an unselected group of patients with other causes of ARF but not when the comparison was with sex- and age-matched controls with ARF. This suggests that this previously described feature of rhabdomyolysis simply reflects the increased muscle mass of a younger group of patients, rather than a specific effect of muscle damage. Clinical features of muscle damage were often absent and so the possibility of rhabdomyolysis should be considered in appropriate settings if the diagnosis is to be made early enough to administer treatment that may prevent ARF and the consequences of the compartment syndrome.

Necrotizing myopathy in critically-ill patients

Skeletal muscle wasting is commonly observed in critically-ill patients and has been attributed to catabolic fibre atrophy and to neuropathy. This study describes the occurrence of a necrotizing myopathy in 15 out of 31 critically-ill patients who had percutaneous biopsies taken from the tibialis anterior muscles. While most cases showed necrosis of isolated fibres, 5 of the 12 patients who had serial biopsies showed progressive necrosis of up to 95 per cent of the fibres. One other case showed infarction and one case had staphylococcal vasculitis. Atrophy of type 1 and/or type 2 fibres was documented by morphometry in 12 cases. Myoglobin-containing casts were demonstrated immunohistochemically in renal tubules on either biopsy or necropsy material in 5 out of 7 cases. The presence of muscle necrosis was a clinically unexpected finding which may contribute to weakness, complicate the interpretation of tissue biochemistry and energy balance studies, and potentiate renal failure. The necrosis is probably multifactorial in origin, with ischaemia and sepsis contributing factors.