Muscular weakness in osteomalacia and hyperparathyroidism

Is it really myositis? Mimics and pitfalls

Idiopathic inflammatory myopathies are a heterogeneous set of systemic inflammatory disorders primarily affecting muscle. Signs and symptoms vary greatly between and within subtypes, requiring supportive laboratory and pathologic evidence to confirm the diagnosis. Several studies are typical assessments for patients with suspected inflammatory myopathy, including muscle enzymes, autoimmune markers, imaging, and muscle biopsy. Misdiagnoses of myositis are not only related to the overlap of clinical phenotype with non-inflammatory myopathies, but also due to the limitations of diagnostic tests employed. Since many of the investigative tests are non-specific, they share features with other disorders, including muscular dystrophies, endocrine, toxic, and metabolic myopathies, and other neuromuscular or rheumatologic conditions. Recognizing the limitations of tests and understanding the shared features between inflammatory and non-inflammatory myopathies can help prevent misdiagnosing myositis with one of its several mimics.

Clinical and laboratory features of patients with osteomalacia initially presenting with neurological manifestations

Patients with osteomalacia often visit the neurology department with conditions mimicking other myopathies. We analyzed clinical features of osteomalacia patients who visited the neurology department. These patients frequently presented with hypocalcemia, hypovitaminosis D, and pain with less severe weakness. Osteomalacia should be considered when patients present with pain and weakness.

INTRODUCTION

Osteomalacia is a disease of bone metabolism; however, some patients with osteomalacia initially visit the neurology department. As these patients often complain of weakness and gait disturbance, osteomalacia can be confused with other myopathies. We analyzed the clinical features of patients with osteomalacia who visited the neurology department.

METHODS

We retrospectively reviewed the medical records. Osteomalacia was diagnosed based on symptoms, laboratory features, and imaging results. We compared the characteristics of patients with osteomalacia who visited the neurology department with (1) those who did not visit the neurology department and (2) patients with idiopathic inflammatory myopathy.

RESULTS

Eighteen patients with osteomalacia visited the neurology department (NR group). The common etiologies in the NR group included tumors or antiepileptic medication, whereas antiviral medication was the most common in patients who did not visit the neurology department (non-NR group). The NR group showed lower serum calcium (p = 0.004) and 25-hydroxyvitamin D (p = 0.006) levels than the non-NR group. When compared with patients with inflammatory myopathy, both groups showed proximal dominant weakness. However, pain was more common in osteomalacia than in myopathy (p = 0.008), and patients with osteomalacia showed brisk deep tendon reflex more often (p = 0.017). Serum calcium (p = 0.003) and phosphate (p < 0.001) levels were lower in osteomalacia than in myopathy.

CONCLUSIONS

It was not uncommon for patients with osteomalacia to visit the neurology department. The clinical presentation of these patients can be more complex owing the superimposed neurological disease and accompanying hypocalcemia. Osteomalacia should be considered when patients present with pain and weakness.

Proximal muscle weakness as a result of osteomalacia associated with celiac disease: a case report

A 24-year-old woman suffering from back and hip pain with difficulty in walking was reported. She had proximal muscle weakness. Laboratory findings led to the diagnosis of osteomalacia. Positivity of antibodies strengthened suspicion of celiac disease. In patients with proximal muscle weakness, osteomalacia should be considered in differential diagnosis even in a young woman.

INTRODUCTION

A 24-year-old woman suffering from back pain, bilateral hip pain, and difficulty in walking was reported. Her symptoms had started in the first trimester of pregnancy.

METHODS

In her physical examination, proximal muscle weakness and waddling gait pattern were determined. Her lumbar spine and hip MRI revealed no obvious pathological findings. Electromyography showed a myophatic pattern.

RESULTS

Physical examination, normal values of creatine kinase, and muscle biopsy were supplied to exclude the diagnosis of primer muscle diseases. Laboratory findings led to the diagnosis of osteomalacia with normal renal function. Gastrointestinal symptoms and positivity of anti-gliadin and anti-endomysium antibodies strengthened the suspicion of celiac disease as a cause of the osteomalacia. The diagnosis of celiac disease was confirmed with duodenal mucosal biopsy.

CONCLUSION

In patients with proximal muscle weakness and waddling gait pattern, osteomalacia should be considered in differential diagnosis even in a young woman and underlying disease should be investigated.

Vitamin D and its role in skeletal muscle

This review discusses the clinical and laboratory studies that have examined a role of vitamin D in skeletal muscle. Many observational studies, mainly in older populations, indicate that vitamin D status is positively associated with muscle strength and physical performance and inversely associated with risk of falling. Clinical trials of vitamin D supplementation in older adults with low vitamin D status mostly report improvements in muscle performance and reductions in falls. The underlying mechanisms are probably both indirect via calcium and phosphate and direct via activation of the vitamin D receptor (VDR) on muscle cells by 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. VDR activation at the genomic level regulates transcription of genes involved in calcium handling and muscle cell differentiation and proliferation. A putative membrane-associated VDR activates intracellular signaling pathways also involved in calcium handling and signaling and myogenesis. Additional evidence comes from VDR knockout mouse models with abnormal muscle morphology and physical function, and VDR polymorphisms which are associated with differences in muscle strength. Recent identification of CYP27B1 bioactivity in skeletal muscle cells and in regenerating adult mouse muscle lends support to the direct action of both 25-hydroxyvitamin D and 1,25(OH)(2)D in muscle. Despite these research advances, many questions remain. Further research is needed to fully characterize molecular mechanisms of vitamin D action on muscle cells downstream of the VDR, describe the effects on muscle morphology and contractility, and determine whether these molecular and cellular effects translate into clinical improvements in physical function.

Vitamin D: an overview of its role in skeletal muscle physiology in children and adolescents

Many children may have insufficient serum concentrations of vitamin D, which could prevent optimal muscle development and function. Vitamin D deficiency in animal models results in negative effects on muscle fiber structure and calcium/phosphorus handling, suggesting an integral role of vitamin D in skeletal muscle function. While there is a dearth of data in humans, the available evidence demonstrates a positive association between vitamin D status and muscle function. This review focuses on the important role of vitamin D in muscle function in children and adolescents who live in North American regions where exposure to ultraviolet B radiation is limited and who are thus at increased risk for vitamin D insufficiency. The effects of vitamin D on muscle cell proliferation and differentiation, muscle fiber structure, and calcium and phosphorus handling are discussed. Moreover, the roles of vitamin D and the vitamin D receptor and their genomic and nongenomic actions in muscle function are explored in depth. Future research should aim to establish a vitamin D status consistent with optimal musculoskeletal development and function in young children.

PKC and PTPα participate in Src activation by 1α,25OH2 vitamin D3 in C2C12 skeletal muscle cells

We previously demonstrated that 1α,25(OH)(2)-vitamin D(3) [1α,25(OH)(2)D(3)] induces Src activation, which mediates the hormone-dependent ERK1/2 and p38 MAPK phosphorylation in skeletal muscle cells. In the present study, we have investigated upstream steps whereby 1α,25(OH)(2)D(3) may act to transmit its signal to Src. Preincubation with the PKC inhibitor Ro318220 demonstrated the participation of PKC in 1α,25(OH)(2)D(3)-dependent Src activation. Of interest, the hormone promoted the activation of δ the isoform of PKC. We also explored the role of PTPα in PKC-mediated Src stimulation. Silencing of PTPα with a specific siRNA suppressed Src activation induced by 1α,25(OH)(2)D(3). Hormone treatment increased PTPα (Tyr789) phosphorylation and PKC-dependent phosphatase activity. Accordingly, 1α,25(OH)(2)D(3) promoted serine phosphorylation of PTPα in a PKC-dependent manner. Confocal immunocytochemistry and co-immunoprecipitation assays revealed that the hormone induces the co-localization of Src and PTPα with PKC participation. Computational analysis revealed that the electrostatic interaction between Src and PTPα is favored when PTPα is phosphorylated in Tyr789. These data suggest that 1α,25(OH)(2)D(3) acts in skeletal muscle upstream on MAPK cascades sequentially activating PKC, PTPα and Src.

Cardiorespiratory fitness is independently associated with 25-hydroxyvitamin D in chronic kidney disease

BACKGROUND AND OBJECTIVES

Vitamin D is an established important contributor to muscle function and aerobic metabolism. Hypovitaminosis D is highly prevalent in CKD patients and is associated with increased cardiovascular (CV) mortality via unknown mechanisms. Because aerobic-exercise capacity strongly predicts future CV events, we hypothesized that vitamin D status could be linked to CV outcomes via an effect on maximum aerobic-exercise capacity in patients with CKD and that this effect may be mediated in part via its actions on muscle strength and functional ability.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline demographic, anthropometric, and biochemical data were collected in a cross-sectional study of patients with moderate CKD. Peak aerobic capacity was determined during treadmill stress testing using metabolic equivalence of tasks. Physical activity was assessed using the Active Australia questionnaire, grip strength by dynamometer, and functional capacity by "Up & Go" testing.

RESULTS

The study included 85 participants (age 59.5 ± 9.7 years, 60% male, 44% diabetic, 92% Caucasian; mean serum 25-hydroxyvitamin D [25-OHD] 78.4 ± 29.4 nmol/L). We demonstrated that 25-OHD status was independently associated with aerobic-exercise capacity (β = 0.2; P = 0.008). Aerobic-exercise capacity was also predicted by younger age, white race, smaller waist circumference, absence of a previous angina history, and increasing weekly physical activity. However, neither muscle strength nor functional ability were significantly associated with 25-OHD.

CONCLUSIONS

Vitamin D is independently associated with aerobic capacity in CKD patients, and this finding is not explained by changes in muscle strength or functional ability.

Vitamin D deficiency associated with self-neglect in the elderly

BACKGROUND

Vitamin D deficiency is common in elders. However, little is known about the implications of vitamin D deficiency in elder self-neglect.

SPECIFIC AIMS

To characterize a group of self-neglecting elders with vitamin D deficiency based on clinical, cognitive, and functional status. Participants. Forty-four self-neglecting elders referred by the Adult Protective Services.

METHODS

Vitamin D status of the self-neglecting elders was based upon serum levels of 25-hydroxyvitamin D (25-OHD). Demographics, cognitive, and functional characteristics of vitamin D deficient self-neglecting elders were described and compared to those without vitamin D deficiency.

RESULTS

Vitamin D deficiency (25-OHD < 25 nmol/L) was detected in 16 out of 44 self-neglecting elders (36%). Self-neglecting elders with vitamin D deficiency had lower scores in the Physical Performance Test and higher scores in the Kohlman Evaluation of Living Skills, compared with those who were not vitamin D deficient (p = 0.014 and p = 0.018 respectively).

CONCLUSIONS

Vitamin D deficiency is common in elder self-neglect. Self-neglecting elders with vitamin D deficiency have impaired physical performance and inadequate living skills, which can be potentially improved by treating vitamin D deficiency.

MAP kinases p38 and JNK are activated by the steroid hormone 1alpha,25(OH)2-vitamin D3 in the C2C12 muscle cell line

In chick skeletal muscle cell primary cultures, we previously demonstrated that 1alpha,25(OH)2-vitamin D3 [1alpha,25(OH)2D3], the hormonally active form of vitamin D, increases the phosphorylation and activity of the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2, their subsequent translocation to the nucleus and involvement in DNA synthesis stimulation. In this study, we show that other members of the MAP kinase superfamily are also activated by the hormone. Using the muscle cell line C2C12 we found that 1alpha,25(OH)2D3 within 1 min phosphorylates and increases the activity of p38 MAPK. The immediately upstream mitogen-activated protein kinase kinases 3/6 (MKK3/MKK6) were also phosphorylated by the hormone suggesting their participation in p38 activation. 1Alpha,25(OH)2D3 was able to dephosphorylate/activate the ubiquitous cytosolic tyrosine kinase c-Src in C2C12 cells and studies with specific inhibitors imply that Src participates in hormone induced-p38 activation. Of relevance, 1alpha,25(OH)2D3 induced in the C2C12 line the stimulation of mitogen-activated protein kinase activating protein kinase 2 (MAPKAP-kinase 2) and subsequent phosphorylation of heat shock protein 27 (HSP27) in a p38 kinase activation-dependent manner. Treatment with the p38 inhibitor, SB203580, blocked p38 phosphorylation caused by the hormone and inhibited the phosphorylation of its downstrean substrates. 1Alpha,25(OH)2D3 also promotes the phosphorylation of c-jun N-terminal protein kinases (JNK 1/2), the response is fast (0.5-1 min) and maximal phosphorylation of the enzyme is observed at physiological doses of 1alpha,25(OH)2D3 (1 nM). The relative contribution of ERK-1/2, p38, and JNK-1/2 and their interrelationships in hormonal regulation of muscle cell proliferation and differentiation remain to be established.

Vitamin D deficiency and secondary hyperparathyroidism are common complications in patients with peripheral arterial disease

OBJECTIVE

To investigate via the vitamin D status whether patients with peripheral arterial disease (PAD) tend to develop vitamin D deficiency that in turn influences their clinical symptoms.

DESIGN

Cross-sectional.

SETTING

University hospital.

PATIENTS AND PARTICIPANTS

Three hundred twenty-seven patients were evaluated; subjects with secondary causes of bone disease or bone active medication were excluded. One hundred sixty-one patients with either PAD stage II (n = 84) or stage IV (n = 77) were enrolled and compared to 45 age- and sex-matched healthy controls.

MEASUREMENTS AND MAIN RESULTS

All patients underwent determinations of serum chemistry, 25-hydroxyvitamin D (vitamin D3) intact parathyroid hormone (iPTH), alkaline phosphatase (ALP), and osteocalcin and were further stratified according to an individual restriction score into 3 groups: mildly, moderately, or severely restricted in daily life due to the underlying disease. Patients with PAD IV showed significantly lower vitamin D3 (P =.0001), and calcium (P =.0001) values and significantly higher iPTH (P =.0001), osteocalcin (P =.0001) and ALP (P =.02) levels as compared to patients with PAD II. Patients considering themselves as severely restricted due to the underlying disease showed lower vitamin D3 and higher iPTH levels than those who described only a moderate (vitamin D3: P <.001; iPTH: P <.01) or mild (vitamin D3: P <.001; iPTH: P <.001) restriction in daily life.

CONCLUSION

Patients with PAD IV, especially those who feel severely restricted due to the disease, are at high risk of developing vitamin D deficiency, secondary hyperparathyroidism, and ultimately osteomalacia due to immobilization and subsequent lack of exposure to sunlight, all of which in turn lead to further deterioration. Monitoring of vitamin D metabolism and vitamin D replacement therapy could be a simple, inexpensive approach to mitigating clinical symptoms and improving quality of life in patients with advanced PAD.

Vitamin D deficiency, muscle function, and falls in elderly people

An inadequate serum vitamin D status is commonly seen in elderly people as the result of various risk factors interacting in this population. Apart from the well-known effects on bone metabolism, this condition is also associated with muscle weakness, predominantly of the proximal muscle groups. Muscle weakness below a certain threshold affects functional ability and mobility, which puts an elderly person at increased risk of falling and fractures. Therefore, we wanted to determine the rationale behind vitamin D supplementation in elderly people to preserve and possibly improve muscle strength and subsequently functional ability. From experimental studies it was found that vitamin D metabolites directly influence muscle cell maturation and functioning through a vitamin D receptor. Vitamin D supplementation in vitamin D-deficient, elderly people improved muscle strength, walking distance, and functional ability and resulted in a reduction in falls and non-vertebral fractures. In healthy elderly people, muscle strength declined with age and was not prevented by vitamin D supplementation. In contrast,severe comorbidity might affect muscle strength in such a way that restoration of a good vitamin D status has a limited effect on functional ability. Additional research is needed to further clarify to what extent vitamin D supplementation can preserve muscle strength and prevent falls and fractures in elderly people.

Involvement of tyrosine kinase activity in 1alpha,25(OH)2-vitamin D3 signal transduction in skeletal muscle cells

In cultured chick skeletal muscle cells loaded with Fura-2, the tyrosine kinase inhibitors herbimycin A and genistein abolished both the fast inositol 1,4,5-trisphosphatedependent Ca(2+) release from internal stores and extracellular Ca(2+) influx induced by 1alpha, 25(OH)(2)-vitamin D(3) (1alpha,25(OH)(2)D(3)). Daidzein, an inactive analog of genistein, was without effects. Tyrosine phosphatase inhibition by orthovanadate increased cytosolic Ca(2+). Anti-phosphotyrosine immunoblot analysis revealed that 1alpha, 25(OH)(2)D(3) rapidly (0.5-10 min) stimulates in a concentrationdependent fashion (0.1-10 nm) tyrosine phosphorylation of several myoblast proteins, among which the major targets of the hormone could be immunochemically identified as phospholipase Cgamma (127 kDa), which mediates intracellular store Ca(2+) mobilization and external Ca(2+) influx, and the growth-related proteins mitogen-activated protein (MAP) kinase (42/44 kDa) and c-myc (65 kDa). Genistein suppressed the increase in phosphorylation and concomitant elevation of MAPK activity elicited by the sterol. Both genistein and the MAPK kinase (MEK) inhibitor PD98059 abolished stimulation of DNA synthesis by 1alpha,25(OH)(2)D(3). The sterol-induced increase in tyrosine phosphorylation of c-myc, a finding not reported before for cell growth regulators, was totally suppressed by the specific Src inhibitor PP1. These results demonstrate that tyrosine phosphorylation is a previously unrecognized mechanism involved in 1alpha,25(OH)(2)D(3) regulation of Ca(2+) homeostasis in hormone target cells. In addition, the data involve tyrosine kinase cascades in the mitogenic effects of 1alpha, 25(OH)(2)D(3) on skeletal muscle cells.

Osteomalacic myopathy

A 45-year-old woman reported the development of thigh pain followed within a year by proximal muscle weakness. Clinical findings included short stature, prominent kyphoscoliosis, proximal weakness, and brisk reflexes. Recognition of an increased level of serum alkaline phosphatase and hypophosphatemia led to the diagnosis of osteomalacia. Identification of iron deficiency anemia and hypocholesterolemia implicated previously unrecognized gluten-sensitive enteropathy with associated vitamin D malabsorption as the cause of the osteomalacia. Adherence to a gluten-free diet and treatment with vitamin D2 resulted in weight gain, resolution of pain, and improvement in strength within 3 months. Painful proximal weakness and hyperreflexia may be the initial and primary manifestations of osteomalacia, a readily treatable cause of muscle and bone disease.

Neuromuscular involvement in mild, asymptomatic primary hyperparathyroidism

PURPOSE

The classic neuromuscular abnormalities of primary hyperparathyroidism are based on observations from an earlier time when the disease presented commonly with signs and symptoms. The purpose of the present study was to test for neuromuscular abnormalities among patients currently seen with primary hyperparathyroidism, in whom the vast majority are asymptomatic.

PATIENTS, METHODS, AND RESULTS

Forty-two patients (30 women, 12 men) were studied. Serum calcium level was 11.1 +/- 0.1 mg/dL (normal, 8.7 to 10.7 mg/dL); phosphorus level was 2.8 +/- 0.1 mg/dL (normal, 2.5 to 4.5 mg/dL). Parathyroid hormone levels by radioimmunoassay for N-terminal and for mid-molecule regions were 32.6 +/- 2.4 pg/mL (normal, 8 to 24 pg/mL) and 831 +/- 127 pg/mL (normal, 50 to 330 pg/mL), respectively. Although generalized weakness and easy fatigability were common complaints, they were not seen on neurologic examination. No patient showed typical neuromuscular findings such as muscle weakness or atrophy, hyperreflexia, abnormal gait, tongue fasciculations, or objective changes in mental status. On the other hand, paresthesias and muscle cramps were reported by 22 patients (52%). Neurologic examination in 12 patients (29%) demonstrated findings consisting of either stocking-glove loss of pain sensation or loss of vibratory sensation with diminished reflexes. Creatine phosphokinase levels were normal in all patients. Electromyography and nerve conduction studies were performed in nine patients. None showed myopathy or signs of motor unit denervation. Isolated nerve abnormalities (n = 6) and nonspecific sensory neuropathy (n = 2) were observed.

CONCLUSION

We conclude that the classic neuromuscular syndrome of primary hyperparathyroidism is rarely seen among a typical modern-day group of patients with primary hyperparathyroidism. The results suggest that the neurologic component of primary hyperparathyroidism should be included among those features of the disease that have changed along with other aspects of the clinical profile of primary hyperparathyroidism.

Muscle function in patients with primary hyperparathyroidism

The muscle contraction of the anterior tibial muscle was investigated by measurements of electrically stimulated and computer-analyzed muscle twitches in 18 unselected patients with primary hyperparathyroidism (HPT) and in 20 healthy control persons. The HPT patients had a lower muscle twitch tension (TT) at single stimulation, compared with the control group [76 +/- 24 N (SD) and 99 +/- 33 N respectively, P less than 0.05]. At high-frequency stimulation the difference in muscle force increased, and at 20 Hz stimulation the force in the HPT patients was 73% of that in the controls (P less than 0.01). There were no differences between the HPT patients and the control persons in neither contraction time nor half relaxation time at single muscle twitch nor in twitch potentiation after 20 and 90 seconds maximal voluntary contraction. The results indicate that patients with primary HPT have an impaired muscle function of probable importance for their symptoms of weakness and generalized fatigue.

Maximal isokinetic muscle strength in patients with primary hyperparathyroidism before and after parathyroid surgery

Primary hyperparathyroidism (HPT) is associated with symptoms of generalized fatigue and muscle weakness. The purpose of this study was to investigate muscular function in HPT quantitatively and to evaluate the effect of parathyroid surgery in this respect. The maximal isokinetic muscle strength (peak torque) of knee extension and flexion was measured with a Cybex-II dynamometer in 16 patients with primary HPT (mean serum calcium 2.81 +/- 0.14 mmol/l), four of whom had subjective impairment of strength, and in nine control patients submitted to hemithyroidectomy due to atoxic thyroid adenoma. Before surgery there was no significant difference in muscle strength between the two groups, neither was there any consistent relationship between the subjective feeling of muscular weakness and the measured peak torque. Seven months after surgery the HPT patients had increased their muscle strength by 8 per cent (P less than 0.05). The improvement was correlated with the pre-operative serum calcium levels (r = 0.56, P = 0.02) and was particularly seen in patients with pre-operative subjective muscular weakness. Patients with only slightly raised calcium values and without subjective muscular symptoms did not benefit clearly from surgery, compared with the controls. The study demonstrates that HPT patients, especially those with neuromuscular symptoms, can improve their muscle strength after parathyroid surgery.

Neuromuscular involvement in primary hyperparathyroidism

Sixteen consecutive patients with primary hyperparathyroidism (HPT) were examined by a combination of electrophysiological, morphological and biochemical measurements. Six patients had, preoperatively, subjective impairment of neuromuscular function. Three of them were improved by the normalization of parathyroid function after surgery. In the other patients, who either had vague symptoms or appeared to be asymptomatic, the operation did not cause subjective changes in their neuromuscular function during a 3-month follow-up period. Altogether seven patients, three of whom had symptoms, had impairment of the neuromuscular transmission as evaluated by the single-fibre EMG technique. The changes were of slight degree and unlikely to be of clinical importance. Two patients had a slightly reduced nerve conduction velocity and in two cases moderate abnormalities were found in muscle biopsy specimens. In conclusion, the muscular weakness reported by HPT patients did not seem to be caused by disturbance of neuromuscular transmission. HPT patients who preoperatively were apparently asymptomatic did not have defects of their neuromuscular transmission that were of clinical significance.

Myopathy as a presentation of coeliac disease

An eight-year-old girl with symptoms and signs of myopathy subsequently was found to suffer from coeliac disease. The myopathy disappeared on a gluten-free diet. It is suggested that the acquired myopathy may be related to deficiency in fat-soluble vitamin D or E, as a result of protracted steatorrhea.

iron-overload-associated myopathy in patients on maintenance haemodialysis: a histocompatibility-linked disorder

Unexplained proximal muscle weakness developed in 10 patients on chronic maintenance haemodialysis. Proximal muscle biopsy in 7 patients disclosed iron deposition in muscle fibres and/or macrophages. All 10 patients had severe iron overload (serum-ferritin level > 1000 ng/ml). Since HLA-A3, B7, and B14 antigens are associated with idiopathic haemochromatosis and, therefore, are linked with alleles regulating iron metabolism, HLA type was reviewed in 61 haemodialysis patients, including the 10 myopathic patients. Serum-ferritin levels showed a significant correlation (p<0.001) with the presence of the HLA-antigens. Close relatives of these patients with HLA-antigen-associated iron-overload myopathy did not have raised serum-ferritin levels. Patients on maintenance haemodialysis who have inherited the "haemochromatosis alleles" thus have an increased risk of iron overload and muscle iron deposition.

Muscle abnormalities in coeliac disease: studies on gross motor development and muscle fibre composition, size and metabolic substrates

In 11 children with coeliac disease gross motor development was assessed before and during diet treatment using the gross motor subscale of the Denver developmental screening test. ATP, creatine phosphate (CP), glycogen and lactate concentrations, muscle fibre size and fibre composition were measured in specimens obtained by needle biopsy from the vastus lateralis muscle. Before treatment, gross motor development was delayed. ATP, and to a lesser extent, CP and glycogen concentrations were lowered compared to a control group. After treatment, gross motor development was normal and no differences in ATP, CP or glycogen concentrations were found compared to the control group. Fibre size seemed unaffected by the disease. The percentage of type 1 fibres was significantly lower before treatment, compared to values obtained during treatment and from the control group. Whether these metabolic changes were due to the coeliac disease per se or the inactivity which it causes was not possible to establish. In humans, only altered neurogenic influence on the muscles has been previously shown to give changes in fibre composition.

Metabolic acidosis in the vitamin D-deficient chick

In vitamin D-deficient chicks raised from age 1 day on a vitamin D-deficient diet, hyperchloremic metabolic acidosis accurred at 3 wk and persisted. Within 24 hr of administration of vitamin D, the acidosis and hypocalcemia were attentuated; during the subsequent 72 hr the severity of the metabolic acidosis but not that of the hypocalcemia was further attenuated. That further attenuation occurred despite hypocalcemia of unchanging severity and presumed continuing secondary hyperparathyroidism suggests the possibility that vitamin D deficiency may be a requirement for the expression of metabolic acidosis. Since in vitro and in vivo studies suggest that subphysiologic values of media and blood pH, respectively, are attended by reduced production of 1,25-(OH2D3, the most biologically active vitamin D metabolite known, the occurrence of acidosis in vitamin D deficiency may compound its metabolic consequences. The possible effects of acidosis must be considered in interpreting results of investigations of vitamin D metabolism in vitamin-D-deficient chicks.

Electromyography in nutritional osteomalacic myopathy

Electromyographic studies in 15 women with nutritional osteomalacia and proximal muscle weakness showed brief duration motor unit action potentials of normal amplitude and increased proportion of polyphasic motor unit potentials in the majority of them. By employing quantitative methods of electromyography, more positive results were obtained, thus reducing the sampling data. The histology showed non-specific muscle fibre atrophy without degenerative changes and the clinical and electromyographic examinations together showed clear evidence of a myopathy, suggesting a reversible transient block of the muscle fibres. Contrary to a recent suggestion, the nature of muscular change in osteomalacia remains the same regardless of its cause being nutritional or otherwise.

Muscle weakness in osteomalacia

The muscle weakness that frequently accompanies osteomalacia and rickets may arise from a variety of causes. Particularly in patients with muscle weakness, identification of the metabolic disorder is important, since effective treatment is often possible.

Nature of muscular change in osteomalacia: light- and electron-microscope observations

Thirteen muscle biopsy specimens (mainly the gluteus maximus) from 12 patients with laboratory confirmation of osteomalacia and proximal muscle weakness in 10 were examined by light and electron microscopy. Light microscopy revealed mild diffuse non-specific atrophy of the muscle fibres in 10 cases, severe generalised atrophy in one and patchy group atrophy in one. There was no myopathic change in specimens from cases with either a nutritional aetiology, or a mixed aetiology. The former, mostly women gave a history of severe chronic malnutrition often accompanied by repeated pregnancies and prolonged lactation; those with a mixed aetiology gave, in addition, evidence of a metabolic or endocrine disorder such as hyperparathyroidism, hyperthyroidism, uraemia, or treatment with anti-epileptic drugs or were of uncertain origin. Electron-microscope examination of muscle from the nutritional group showed atrophic changes in the fibres, such as loss of myofibrils, prominence of mitochondria and glycogen, loosening and folding of the basement-membrane but good preservation of the remaining myofibrils. In contrast muscle from cases of mixed aetiology showed, in addition to the atrophic features, clear degenerative changes in the myofibrils and the mitochondria, accumulation of amorphous material at the site of myofibrillar loss and of lipofuscin in muscle fibres, vascular endothelium and satellite cells. The earliest degenerative change was in the "I" band, involving actin filaments and "Z" line. The triads were generally preserved but the sarcoplasmic reticulum appeared affected in a patient with tetany and severe mitochondrial degeneration. In a patient with thyrotoxicosis, proliferation of central nuclei, "Z" line streaming and formation of "T" tubular aggregates were seen. In one patient with hyperparathyroidism and hypercalcaemia, severe myofibrillar degeneration and mitochondria showing osmiophilic deposits, possibly of calcium phosphate, were encountered. It is concluded: (1) that all osteomalacic muscle weakness is not myopathic but a non-specific atrophy occurring probably on the basis of disuse and malnutrition, and (2) patients with an added metabolic or endocrinological disorder show in addition to the atrophy, degenerative changes in the muscle fibre and its sub-cellular components consistent with myopathy, and these patients should be clearly distinguished from those with a background of malnutrition only.

Myopathy in hypophosphataemic osteomalacia presenting in adult life

Three cases of hypophosphataemic osteomalacia presenting in adult life, in which a myopathy was a prominent presenting feature, are described. In one, a nasopharyngeal haemangioma was also present. Possible mechanisms underlying the myopathy are discussed briefly.