Corticosteroid-induced myopathy and the respiratory muscles. Report of two cases

Clinical and pathological aspects of toxic myopathies

As the most frequent cause of acquired myopathy, toxic myopathies are characterised by clinicopathological features that vary depending on the mode of action of the drugs or toxins involved. Although a large number of substances can induce myotoxicity, the main culprits are statins, alcohol, and corticosteroids. A rigorous, well-organised diagnostic approach is necessary to obtain a rapid diagnosis. For early diagnosis and management, it is important for clinicians to be aware that most toxic myopathies are potentially reversible, and the goal of treatment should be to avoid serious muscle damage.

GLUCOCORTICOID EXCESS IN BONE AND MUSCLE

Glucocorticoids (GC), produced and released by the adrenal glands, regulate numerous physiological processes in a wide range of tissues. Because of their profound immunosuppressive and anti-inflammatory actions, GC are extensively used for the treatment of immune and inflammatory conditions, the management of organ transplantation, and as a component of chemotherapy regimens for cancers. However, both pathologic endogenous elevation and long-term use of exogenous GC are associated with severe adverse effects. In particular, excess GC has devastating effects on the musculoskeletal system. GC increase bone resorption and decrease formation leading to bone loss, microarchitectural deterioration and fracture. GC also induce loss of muscle mass and strength leading to an increased incidence of falls. The combined effects on bone and muscle account for the increased fracture risk with GC. This review summarizes the advance in knowledge in the last two decades about the mechanisms of action of GC in bone and muscle and the attempts to interfere with the damaging actions of GC in these tissues with the goal of developing more effective therapeutic strategies.

Markers of inflammation and disuse in vastus lateralis of chronic obstructive pulmonary disease patients

BACKGROUND

Disuse and/or local inflammation in the muscle cannot be excluded as potential influences for the decreased muscle force in patients hospitalised due to an acute chronic obstructive pulmonary disease (COPD) exacerbation. This study aims to compare expression levels of markers of disuse (insulin-like growth factor-1 (IGF-I), MyoD and myogenin) and inflammation [interleukin-6 (IL-6), IL-8 and tumour necrosis factor-alpha (TNF-alpha)] in the muscle of hospitalised and stable COPD patients and healthy elderly.

MATERIAL AND METHODS

Muscle biopsies (m. vastus lateralis) were taken in 14 hospitalised COPD patients (aged 68 +/- 8), 11 clinically stable COPD patients (aged 68 +/- 9) and seven healthy subjects (aged 70 +/- 7) to analyse local mRNA expression levels of IL-6, IL-8, TNF-alpha, IGF-I and protein expression levels of IGF-I, MyoD and myogenin. Relationships of these expression levels with lung and skeletal muscle function were investigated.

RESULTS

IGF-I mRNA and MyoD protein levels were significantly lower in hospitalised patients compared to healthy subjects. MyoD protein levels were positively related to quadriceps force. Muscle IL-6 and IL-8 expression in hospitalised patients was similar compared to stable patients and healthy subjects and was not related to expression levels of muscle markers of disuse or quadriceps force. Muscle TNF-alpha and myogenin were not detected.

CONCLUSION

Decreased expression levels of muscle IGF-I and MyoD in hospitalised patients suggest a potential influence of disuse in the increased muscle weakness during an acute COPD exacerbation. This study did not find any evidence supporting local inflammation via IL-6, IL-8 and/or TNF-alpha in the vastus lateralis muscle of COPD patients.

Acute rhabdomyolysis complicating status asthmaticus in children: case series and review

OBJECTIVES

To describe a case series of 4 children who developed acute rhabdomyolysis as a complication of acute respiratory failure secondary to status asthmaticus.

METHODS

A retrospective review of all children who were admitted to our pediatric intensive care unit (PICU) with status asthmaticus from November 1998 through July 2004 was performed and all children who developed acute rhabdomyolysis, defined as a 5-fold increase above the upper limit of normal in the serum creatine phosphokinase (CPK) concentration (CPK > or = 1250 IU/L), were identified. Demographic and clinical data were abstracted from the medical record.

RESULTS

During the study period, 108 children with status asthmaticus were admitted to our PICU (3.6% of all admissions). Four children (age 12-19 years) developed acute respiratory failure requiring mechanical ventilation, and all 4 of these children (3.7% of all children with status asthmaticus admitted to the PICU) developed acute rhabdomyolysis. The 4 children who developed acute rhabdomyolysis were older than the children with status asthmaticus, without rhabdomyolysis (median age 15 years vs. 5 years).

CONCLUSIONS

Acute rhabdomyolysis complicating status asthmaticus may be more common than previously ascertained. We therefore suggest that CPK levels should be followed closely in all children with status asthmaticus and acute respiratory failure. The early presentation of rhabdomyolysis in the current series suggests that factors other than corticosteroids and neuromuscular blockers are potentially involved. Mechanical ventilation and older age seem to be significant risk factors for rhabdomyolysis, perhaps implicating a mechanism similar to the pathogenesis of severe exercise-related rhabdomyolysis. Further clinical study of the incidence and causative factors of rhabdomyolysis in this population is warranted.

Quadriceps weakness is related to exercise capacity in idiopathic pulmonary fibrosis

STUDY OBJECTIVE

In COPD, it has been shown that peripheral muscle dysfunction is a factor determining exercise intolerance. We examined the hypothesis that exercise capacity of patients with idiopathic pulmonary fibrosis (IPF) is, at least in part, determined by peripheral muscle dysfunction.

METHODS

Maximum oxygen uptake (V(O2)max) was evaluated in 41 consecutive patients with IPF, along with potential determinants of exercise capacity, both in the lungs and in the peripheral muscles.

RESULTS

Patients had reduced V(O2)max (893 +/- 314 mL, 46.0% predicted) and reduced quadriceps force (QF) [65% predicted]. Significant correlates of V(O2)max reduction were vital capacity (VC) [r = 0.79], total lung capacity (r = 0.64), diffusion capacity (r = 0.64), QF (r = 0.62), maximum expiratory pressure (r = 0.48), and Pa(O2) at rest (r = 0.33). In stepwise multiple regression analysis, VC and QF were independent predictors of V(O2)max. Furthermore, in subgroup analysis, QF was a significant contributing factor for V(O2)max in patients who discontinued exercise because of dyspnea and/or leg fatigue.

CONCLUSIONS

We conclude that QF is a predictor of exercise capacity in IPF. Measures that improve muscle function might improve exercise tolerance.

Clenbuterol antagonizes glucocorticoid-induced atrophy and fibre type transformation in mice

Beta-agonists and glucocorticoids are frequently coprescribed for chronic asthma treatment. In this study the effects of 4 week treatment with beta-agonist clenbuterol (CL) and glucocorticoid dexamethasone (DEX) on respiratory (diaphragm and parasternal) and limb (soleus and tibialis) muscles of the mouse were studied. Myosin heavy chain (MHC) distribution, fibres cross sectional area (CSA), glycolytic (phosphofructokinase, PFK; lactate dehydrogenase, LDH) and oxidative enzyme (citrate synthase, CS; cytochrome oxidase, COX) activities were determined. Muscle samples were obtained from four groups of adult C57/B16 mice: (1) Control (2) Mice receiving CL (CL, 1.5 mg kg(-1) day(-1) in drinking water) (3) Mice receiving DEX (DEX, 5.7 mg kg(-1) day(-1) s.c.) (4) Mice receiving both treatments (DEX + CL). As a general rule, CL and DEX showed opposite effects on CSA, MHC distribution, glycolytic and mitochondrial enzyme activities: CL alone stimulated a slow-to-fast transition of MHCs, an increase of PFK and LDH and an increase of muscle weight and fibre CSA; DEX produced an opposite (fast-to-slow transition) change of MHC distribution, a decrease of muscle weight and fibre CSA and in some case an increase of CS. The response varied from muscle to muscle with mixed muscles, as soleus and diaphragm, being more responsive than fast muscles, as tibialis and parasternal. In combined treatments (DEX + CL), the changes induced by DEX or CL alone were generally minimized: in soleus, however, the effects of CL predominated over those of DEX, whereas in diaphragm DEX prevailed over CL. Taken together the results suggest that CL might counteract the unwanted effects on skeletal muscles of chronic treatment with glucocorticoids.

Iatrogenic-induced dysfunction of the neuromuscular respiratory system

In the presence of respiratory symptoms that are associated with alveolar hypoventilation or a restrictive ventilatory defect and in the absence of parenchymal or pleural abnormalities on the chest radiograph, iatrogenic causes must be evoked, exactly as they are in the presence of interstitial lung disease. In most cases, the anamnestic and clinical contexts provide a strong diagnostic presumption. It is important to establish carefully the mechanism of the observed disorders, using the currently available arsenal of diagnostic tools for clinical and prognostic reasons and from a medicolegal standpoint. It is necessary to evaluate precisely the clinical repercussions of the respiratory neuromuscular abnormality to serve as a basis for follow-up and to discuss therapeutic options in certain cases (eg, nocturnal ventilation to correct nocturnal hypoventilation due to diaphragmatic dysfunction, diaphragm plication to alleviate dyspnea after complete phrenic nerve destruction, phrenic nerve pacing), again in the perspective of medicolegal actions.

Glucocorticoid-induced alterations in the rate of diaphragmatic fatigue

These experiments tested the hypothesis that in vitro diaphragmatic fatigue resistance is enhanced in animals treated with glucocorticoids. Female Sprague-Dawley rats (4 months old) were randomly assigned to a control (N =12) or glucocorticoid treatment group (N =12). Treatment animals were injected daily for 8 days with prednisolone (5 mg kg(-1)); control animals were injected with the same volume of the vehicle. Twenty-four hours after the last injection, the following in vitro diaphragmatic contractile properties were examined in costal diaphragm strips: maximal twitch (P(t)) half time to peak tension (1/2 TPT), half relaxation time (1/2 RT), force-frequency relationship, and the rate of fatigue development. Diaphragmatic fatigue was assessed by monitoring the decrease in force production (measured as percent of initial force) over a 60-min contractile period. The in vitro fatigue protocol incorporated a supramaximal stimulus delivered at 30 Hz every 2 s with a train duration of 250 ms (duty cycle 12.5%). Citrate synthase (CS), superoxide dismutase (SOD), and water content of the costal diaphragm were also determined. Glucocorticoid administration induced an 18.9% (P<0.05) decrease in animal body weight when compared to the control. Similar weight losses also occurred in the diaphragm with a decrease (P<0.05) in mass of 16.5% compared to the control. Furthermore, prednisolone treatment resulted in a significant reduction in the cross-sectional area (CSA) of type IIb fibres with no change in the CSA area of type I and IIa fibres. 1/2 TPT and 1/2 RT were significantly prolonged (P<0.05) in the glucocorticoid treated rats whereas the force-frequency curve was unaltered (P>0.05). Fatigue resistance was greater in the glucocorticoid group (P<0.05); the relative force production differed between groups at the end of 1 min of contractions and remained different throughout the 60-min fatigue protocol. Citrate synthase, SOD, and water content were not different between groups. These experiments support the hypothesis that costal diaphragm strips of glucocorticoid-treated rats possess a greater resistance to fatigue. We postulate that this fatigue resistance is due to glucocorticoid-induced changes muscle fibre type composition.

Effects of steroid on diaphragmatic functions in rabbits

The effects of steroid on diaphragmatic contractility and endurance were examined in 24 New Zealand rabbits. Diaphragmatic contractility was determined by measuring gastric pressure (Pga) with the lower thorax and the abdomen of the animal being fixed with a rigid cast. Endurance procedure was done by continuous 15 Hz stimulation of the bilateral phrenic nerves, and diaphragmatic endurance was expressed as the time from the initiation of the endurance procedure to the moment when transdiaphragmatic pressure 15 Hz (Pdi-15 Hz) decreased to 25% of Pdimax-15 Hz. Our data suggested that intravenous administration of dexamethasone 2.5 mg daily for 7 days did not affect the diaphragmatic contractility significantly, but could cause a significant decrease in diaphragmatic endurance. When delivered intravenously at the dose of 2.0 mg daily for 14 days, dexamethasone induced a significant decrease both in diaphragmatic contractility and endurance. The recovery of the diaphragmatic strength from fatigue, however, was not influenced by dexamethasone in either circumstance. The influence of dexamethasone on diaphragmatic contractility and endurance may have important clinical implications.

Cortisone-induced changes in myosin heavy chain distribution in respiratory and hindlimb muscles

In this study the effects of administration of cortisone acetate (100 mg kg-1 body weight subcutaneously for 11 days) on distribution and cross-sectional area of different fibre types of rat skeletal muscles were investigated. Diaphragm, parasternal intercostal (PI), extensor digitorum longus (EDL) and soleus muscles were examined in cortisone treated animals (CA) in comparison with ad libitum controls (CTRL) and pair-fed (PF) controls. Four fibre types (I or slow and IIA, IIX, IIB or fast) were identified on the basis of their myosin heavy chain composition using a set of monoclonal antibodies. In CA rats the reduction of cross-sectional area was above 30% in IIX fibres of diaphragm, IIB fibres of PI and in all fast fibres of EDL. In all muscles slow fibres were spared from atrophy. Significant variations in fibre type distribution were found in the muscles of CA rats when compared to CTRL. The percentage of IIB fibres decreased in EDL, PI and diaphragm. This decrease was accompanied by an increase in the percentage of IIA fibres in the same muscles. No changes in the percentage of slow fibres and of fast IIX fibres were observed in EDL, PI and diaphragm of CA rats in comparison with CTRL. In soleus of CA rats the proportion of IIA fibres was lower than in CTRL. In EDL of PF rats atrophy of IIA fibres and changes in fibre type distribution were similar to those observed in CA rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Proximal muscle weakness in a patient with hepatocellular carcinoma

Asthenia and generalized weakness are common in cancer patients. There are multiple causes for these symptoms. We describe a case of rapid onset of proximal muscle weakness in a patient with hepatocellular carcinoma. The differential diagnosis of muscle weakness in the palliative care patient is reviewed. The discussion centers on steroid myopathy and its treatment.

The effect of corticosteroids on inspiratory muscle performance in humans

Functional alterations in the inspiratory muscles were evaluated in patients receiving corticosteroids for diseases other than respiratory. Inspiratory muscle strength, as expressed by the maximal inspiratory mouth pressure (PImax), and inspiratory muscle endurance (PmPeak/PImax), using a pressure threshold breathing device, were evaluated in eight patients with normal pulmonary and inspiratory muscle functions (two patients with rapidly progressive glomerulonephritis, two with glomerulonephritis with minimal changes, two with idiopathic thrombocytopenic purpura, and two with subacute thyroiditis). There was a gradual decrease in both inspiratory muscle strength and endurance following corticosteroid administration. After 8 weeks of treatment PmPeak/PImax decreased from 84.4 +/- 2.4 to 67.9 +/- 3.1 percent (p < 0.001), while inspiratory muscle strength dropped from 126.9 +/- 9.6 to 86.5 +/- 7.4 cm H2O (p < 0.005). Gradual steroid dosage tapering resulted in marked improvement in both strength and endurance; the inspiratory muscle strength rose significantly to 112.2 +/- 8.1 cm H2O (p < 0.0005) when steroid treatment was stopped, and even more significantly 6 months later (to 123.1 +/- 8.1 cm H2O [p < 0.0001]), and the PmPeak/PImax rose to 60.6 +/- 3.4 percent (p < 0.001) and to 74.7 +/- 3.2 percent (p < 0.0001), respectively. We conclude that corticosteroids have a significant deteriorating effect on respiratory muscle function in humans. This weakness is reversible while tapering steroid dosage. Steroid therapy should be reconsidered in patients with underlying lung disease.

Triamcinolone and prednisolone affect contractile properties and histopathology of rat diaphragm differently

Diaphragm atrophy and weakness occur after administration of massive doses of corticosteroids for short periods. In the present study the effects of prolonged administration of moderate doses of fluorinated and nonfluorinated steroids were investigated on contractile properties and histopathology of rat diaphragm. 60 rats received saline, 1.0 mg/kg triamcinolone, or 1.25 or 5 mg/kg i.m. prednisolone daily for 4 wk. Respiratory and peripheral muscle mass increased similarly in control and both prednisolone groups, whereas triamcinolone caused severe muscle wasting. Maximal tetanic tension averaged 2.23 +/- 0.54 kg/cm2 (SD) in the control group. An increased number of diaphragmatic bundles in the 5-mg/kg prednisolone group generated maximal tetanic tensions < 2.0 kg/cm2 (P < 0.05). In addition, fatigability during the force-frequency protocol was most pronounced in this group (P < 0.05). In contrast, triamcinolone caused a prolonged half-relaxation time and a leftward shift of the force-frequency curve (P < 0.05). Histological examination of the diaphragm showed a normal pattern in the control and 1.25-mg/kg prednisolone group. Myogenic changes, however, were found in the 5-mg/kg prednisolone group and, more pronounced, in the triamcinolone group. Selective type IIb fiber atrophy was found in the latter group, but not in the prednisolone groups. In conclusion, triamcinolone induced type IIb fiber atrophy, resulting in reduced respiratory muscle strength and a leftward shift of the force-frequency curve. In contrast, 5 mg/kg prednisolone caused alterations in diaphragmatic contractile properties and histological changes without fiber atrophy.

Respiratory muscles in endocrinopathies

The aim of this review was to demonstrate that RM function is altered in various endocrinopathies and that RM weakness is a common finding. RM function has been well-studied in diseases such as thyroid dysfunction, and steroid induced RM myopathies. Less well documented reports on RM function were found in parathyroid dysfunctions, disorders of mineralocorticoids and pituitary disturbances. Controversial reports were found in diabetes mellitus. No report was found connecting RM function with androgens, pheochromocytoma or adrenaline deficiency in humans. These diseases could potentially cause RM impairment leading to severe respiratory failure (pump failure) putting life in great danger. Therefore, it is obvious that further studies are needed to investigate the performance of RMs in endocrinopathies. Such studies are extremely urgent in Cushing's and Addison's disease, acromegaly, disorders of the adrenal medulla, and in diabetes insipidus.

Corticosteroid-induced myopathy involving respiratory muscles in patients with chronic obstructive pulmonary disease or asthma

We made observations on two patients with asthma and one with COPD who developed steroid-induced myopathy during prolonged treatment with high doses of corticosteroids. On admission, quadriceps force was on the average reduced to 31% of predicted (range 16 to 46% of predicted, nondominant leg), and urinary excretion of creatine in 24 h averaged 687 mg (range 275 to 1,045 mg/24 hr). Respiratory muscle involvement was evidenced by reductions in PImax and PEmax, being 38% (range 36 to 39) and 48% of predicted (range 36 to 68), respectively. Tapering of treatment with corticosteroids resulted in important recovery of quadriceps force and respiratory muscle force. In all three patients, a correlation between muscle forces and steroid dose was present during reduction of the dose. After 6 months quadriceps force averaged 62% of predicted (range 31 to 85), and PImax and PEmax reached 74% (range 52 to 92) and 92% of predicted (range 80 to 106), respectively, after 3 months. Consequently, respiratory muscle force appeared to recover faster than quadriceps force. The implications of these observations for patients treated with the usual doses of corticosteroids for shorter periods require further investigation.

Myasthenia gravis and steroid-induced myopathy of the respiratory muscles

OBJECTIVE

We report a case of corticosteroid-induced myopathy with involvement of respiratory muscles observed in a myasthenic patient.

PATIENT

A 37-years-old woman, under corticosteroid treatment for two years for typical myasthenia gravis was admitted to ICU for acute myasthenic respiratory failure. Weaning from mechanical ventilation remained impossible despite 4 plasma exchanges and azathioprine. The patient exhibited a progressive 12 kg weight loss with muscular weakness and atrophy.

MEASUREMENTS AND RESULTS

Peripheral and diaphragmatic electromyography as well as histological study were consistent with a steroid-induced myopathy. Discontinuation of corticosteroid treatment was followed by a rapid weight gain with general improvement and allowed weaning from mechanical ventilation with a complete recovery.

CONCLUSION

This case provides evidence that corticosteroid-induced myopathy may be observed in myasthenia gravis and may involve the respiratory muscles as well as the peripheral musculature.

Corticosteroid therapy and respiratory muscle function in humans

We examined the effects of prednisone administration on respiratory muscle function in humans using a double-blind study with a placebo control group. A total of 16 normal subjects were randomized to receive 20 mg prednisone daily (n = 8) or placebo daily (n = 8) for 2 wk. Inspiratory muscle strength (Pimax), expiratory muscle strength (PEmax), diaphragmatic strength (Pdimax), and inspiratory muscle endurance were measured at the beginning and end of the study. There was no significant change with treatment for Pimax (-145 +/- 7 to -138 +/- 6 cm H2O), PEmax (171 +/- 17 to 169 +/- 14 cm H2O), Pdimax (194 +/- 11 to 196 +/- 12 cm H2O), or endurance (76 +/- 3 to 77 +/- 4%) for the prednisone group and no significant difference between the two groups. We conclude that prednisone in moderate dosage has no significant effect on respiratory muscle function in humans, at least in the short term.

Drug-induced myopathies

Myopathies are not an unusual complication of drug therapy. The major symptoms in drug-induced myopathies are proximal muscle weakness, increased muscle enzyme levels, electromyographic changes and histological lesions. Some drug-induced myopathies are associated with neuropathy. Drug-induced myopathies can be classified according to the presence or absence of muscular pain and associated neuropathy. Among painless myopathies, we can distinguish myopathies without neuropathy (corticosteroids), myopathies with neuropathy (colchicine, chloroquine and hydroxychloroquine) and myasthenic syndromes (D-penicillamine, antibiotics, beta-blockers). Among painful myopathies, the classification is similar: painful myopathies may or may not be associated with neuropathies. Painful myopathies include polymyositis (D-penicillamine, cimetidine, zidovudine) and other myopathies without polymyositis (clofibrate, statines, cyclosporin). Among the painful neuromyopathies, eosinophilia-myalgia syndrome is a recently described disorder associated with the use of L-tryptophan. Combinations of drugs (for example, a fibrate and a statine or cyclosporin and colchicine) can induce severe myopathies. If such drugs are used together a vigorous surveillance to detect any sign of myopathy is warranted. Instead of classifying drug-induced myopathies according to clinical features, a histological classification can be proposed. Many drugs can induce vacuolar myopathy (colchicine, chloroquine, amiodarone, cyclosporin, drugs causing hypokalaemia and lipid-lowering agents), some others cause a mitochondrial myopathy (zidovudine) or a necrotizing myopathy as seen with vincristine. Overall, several criteria for reporting drug-induced myopathy can be recommended: lack of pre-existent muscular symptoms, a free period between the beginning of the treatment and the appearance of symptoms, lack of another cause accounting for the myopathy, and complete or incomplete resolution after withdrawal of the treatment. Rechallenge of the treatment is not advisable because of the risk of a serious relapse. The exact mechanisms by which drugs cause myopathies are unknown. Some cases may be due to metabolic changes, whereas others may be immune mediated. Nevertheless, the aspect these conditions have in common is the regression of the myopathy with the discontinuation of the drug.