Muscle biopsy and the clinical course of infantile spinal muscular atrophy

Eight infants with severe early infantile spinal muscular atrophy diagnosed by clinical presentation and muscle biopsy were studied. The extent of alterations in muscle histology, histochemistry, and ultrastructure did not reflect the relative severity of the clinical presentation or the course of the illness. In seven biopsies, ultrastructural studies demonstrated empty sleeves of basal lamina projecting from the surface of small myofibers. We conclude that severe infantile spinal muscular atrophy often results in myofiber atrophy similar to that found in other motor neuron diseases, and it is not solely a hypotrophic process. Muscle biopsy findings are important because they help to establish the diagnosis, but they do not help predict the severity of disease among infants with this condition.     

A case of severe infantile form of congenital nemaline myopathy with extensive fatty replacement of the skeletal muscles

A case of severe infantile form of congenital nemaline myopathy who developed extensive fatty replacement of the skeletal muscles was described. A girl was born with severe hypotonia and flaccidity of the extremities. She was put on a ventilator because of the severe respiratory insufficiency. Muscle biopsy performed at 3 months of age revealed numerous nemaline rods in myofibers. She had an anoxic episode at 2 years of age and fell into a vegetative state after that. Serum creatine kinase and aldolase levels were normal. At 8 years of age, X-ray CT scan of the skeletal muscles revealed diffuse and severe fatty replacement of the skeletal muscles of the trunk and extremities; this was far more extensive than in the case of Duchenne muscular dystrophy of similar age. Second muscle biopsy performed in the anterior tibialis muscle at the age of 8 years revealed atrophic muscle fibers and extensive proliferation of connective and fatty tissues. Electron microscopy revealed, numerous rod-containing muscles fibers with severe disorganization and loss of myofilaments. Sural nerve biopsy performed at the same time showed decreased number of large myelinated fibers. Although a possibility could not be excluded completely that the episode of anoxia and chronic debilitation may have contributed to these pathological neuromuscular findings, it was presumed that severe degeneration and fatty replacement of the skeletal muscles progress rapidly after birth in some cases of severe infantile form of congenital nemaline myopathy.     

A newborn with spinal muscular atrophy type 0 presenting with a clinicopathological picture suggestive of myotubular myopathy

We report a male term newborn with genetically confirmed spinal muscular atrophy type 0, presenting with arthrogryposis and severe generalized weakness and requiring ventilatory support. Muscle biopsy revealed fibers with central nuclei resembling myotubes and negative myotubularin immunohistochemical staining compared with a control muscle biopsy. The absence of myotubularin associated with survival motor neuron protein deficiency suggests that survival motor neuron protein may have a role in muscle fiber maturation and myotubularin expression. Studying the pathology of this rare and lethal neonatal form of spinal muscular atrophy may further our understanding of spinal muscular atrophy pathogenesis.     

Congenital myopathy with type II muscle fiber hypoplasia

We examined a 14-month-old boy with severe muscular hypotonia and weakness. Loss of tendon reflexes were noted at age 2 months. Right-sided heart failure and dyspnea during sleep developed at age 4 months. Muscle biopsy revealed selective hypoplasia of type II fibers and normal type I fibers. Intercostal and diaphragmatic muscles showed similar changes at necropsy and probably accented the respiratory failure.     

Muscle nuclear size in neuromuscular disease.

Nuclear size has been estimated in muscle biopsy specimens from seven healthy individuals, eight patients with infantile spinal muscular atrophy (types I and II), and eight patients with Duchenne muscular dystrophy. The results indicate a great increase in nuclear size in Duchenne muscular dystrophy but not in spinal muscular atrophy when compared with controls. The reasons for this finding are discussed in relation to the pathogenesis of these two groups of diseases.     

Vimentin and desmin in maturing skeletal muscle and developmental myopathies.

I studied vimentin and desmin immunoreactivities in the skeletal muscle of 30 human fetuses and children ranging from 8 weeks' gestation to 2 years of age, and in 45 infants and children and five adults with developmental neuromuscular diseases. Acridine orange-RNA fluorescence also identified regenerating myofibers in Duchenne muscular dystrophy and dermatomyositis for comparison with congenital myopathies. Vimentin and desmin are both strongly expressed in fetal myotubes and their immunohistochemical demonstration persists until 36 weeks' gestation. These cytoskeletal proteins are uniformly expressed in myofibers of neonates with X-linked recessive myotubular myopathy. Desmin but not vimentin is diffusely increased in infantile cases of myotonic dystrophy, in some cases of congenital muscle fiber-type disproportion, and in cerebrohepatorenal disease. In nemaline rod myopathy, desmin is focally increased in perinuclear zones and in regions of aggregated rods. The small myofibers in infantile spinal muscular atrophy show increased vimentin and desmin in the subsarcolemmal region. The demonstration of these intermediate filament proteins provides markers to enhance diagnostic precision in the interpretation of the infant muscle biopsy. Furthermore, persistently high fetal concentrations of vimentin/desmin may play a role in the pathogenesis of some developmental myopathies.     

The natural history of infant spinal muscular atrophy in China: a study of 237 patients

The authors retrospectively studied the natural history of 237 patients with infantile spinal muscular atrophy in China. The onset ages (mean ± SD) for types I to III were 3.1 ± 2.7, 8.7 ± 3.8, and 21.1 ± 11.7 months, respectively. The survival probabilities for type I patients at 1, 2, and 5 years were 44.9%, 38.1%, and 29.3%, respectively, and for type II patients, the probabilities were 100%, 100%, and 97%, respectively. All type III patients were alive. Type I patients with onset age after 2 months had significantly increased survival than those with onset before 2 months (P < .05). It should be noticed that survival probability at 2 years in type I patients in our study was close to that in other Asian samples of spinal muscular atrophy, but slightly better than that among whites. Patients accepted minimal proactive interventions other than antibiotics for pulmonary infection, so our study provides reliable baseline data of natural history of spinal muscular atrophy in China.     

Fatal infantile X-linked neuropathy

We report a pedigree with severe X-linked neuropathy that occurs in male infants and results in death, typically by 2 years of age. The proband of our report was weak with preserved mentation. He underwent extensive evaluation, which revealed abnormal nerve conduction studies, neurogenic changes on muscle biopsy, a decreased number of large myelinated fibers and rare onion bulb formations on nerve biopsy, negative gene testing for spinal muscular atrophy, CMT1a, and CMTX1 and a normal brain magnetic resonance image. The proband's mother, an obligate carrier, had normal nerve conduction studies. Male infants with a spinal muscular atrophy phenotype but normal genetic studies should be evaluated for this fatal X-linked neuropathy.     

Striated muscle in protein malnutrition: an experimental study in albino rats

The effects of undernutrition on the "gastrocnemius plantaris" muscle of young albino rats were observed with light and electronmicroscopy and were compared with controls. Pregnant rats received a diet containing 6.7% protein and the neonates had a 3.2% protein diet after weaning. A total number of 40 animals were distributed in two groups: one hypoproteic and one control. Half of the animals of each group were killed 15 days after birth and the remaining ones at 30 days. We could observe important reduction in the weight of the undernourished rats reaching about 50% when compared with the control animals. An important reduction in the diameter of muscle fibers was noted in undernourished rats. Histochemical reactions showed that not only the type I but also the type II fibers were involved, the latter being more severely reduced in size. Type II fibers os small diameter, resembling F (fetal) fiber were found in animals at 15 days indicating a delay in maturation. Ultrastructural evaluation of the muscle did not show specific changes except for a severe reduction in the caliber of fibers when compared with control animals. We concluded that there was hypoplasia and not atrophy of the muscular tissue in animals submitted to pre- and post-natal undernutrition. The present study, associated with others in which the spinal motor cells and peripheral nerves of undernourished rats were analysed, allow us to consider that with protein deprivation there is a delay in the development, a hypoplasia of the motor unit. We think that in infantile progressive spinal amyotrophy (Werdnig-Hoffmann disease) there is possibly hypoplasia and not atrophy of the type II fibers and we postulate that a metabolic proteic problem is involved in this disease.     

Mitochondrial respiratory complex I deficiency simulating spinal muscular atrophy

Two female patients with clinical features resembling spinal muscular atrophy were presented. Patient 1 presented with hypotonia and proximal weakness of extremities at age 4 months. Electromyography revealed motor neuronopathy suggestive of spinal muscular atrophy. Patient 2 presented with severe hypotonia, motor weakness, and joint contractures since birth. Muscle biopsy findings were consistent with spinal muscular atrophy. However, deletions in the survival motor neuron gene and the neuronal apoptosis inhibitor protein gene were not found in both patients. They finally manifested clinical features unlike spinal muscular atrophy: epileptic seizure, cardiomyopathy, and spasticity. The clinical course of each patient was not like that of spinal muscular atrophy type I. Mitochondrial respiratory chain complex enzyme activities in cultured skin fibroblasts were measured. Respiratory complex I enzyme activity was decreased, suggestive of isolated complex I deficiency in both patients. In conclusion, in patients who have clinical features resembling spinal muscular atrophy but no deletions in the spinal muscular atrophy gene, the possibility of the mitochondrial respiratory chain complex I deficiency should be considered.     

Possible neurogenic factor in muscular dystrophy: its similarity to denervation atrophy

Muscle biopsy specimens from 179 cases of muscular dystrophies and from 140 cases of anterior horn cell disorders (from a total of 1,348 biopsied patients) were examined histologically. There were 72 cases of Duchenne type muscular dystrophy (DMD), five of Becker type MD, four girls with myopathy resembling DMD, 40 with limb-girdle, 10 with facioscapulohumeral, seven with late onset, 13 with congenital, and 28 with unclassifiable muscular dystrophies. Groups of small atrophied muscle fibres were encountered in 42 (23%) of the cases in this group, most frequently in patients with limb-girdle, facioscapulohumeral, and least frequently with DM dystrophy. In the second group there were 25 cases of infantile, 38 of juvenile, and 39 of adult spinal muscular atrophy (SMA); there were 21 patients with motor neurone disease (MND), six with poliomyelitis, and 11 with an unclassifiable type of anterior horn cell disorder. Pseudomyopathic changes were encountered in 43 (30%) of all cases in this group. They were most frequently present among patients with juvenile and adult SMA and in those with MND. The presence of group atrophy in muscular dystrophy is considered significant myopathological evidence of a denervation process. On the other hand, pseudomyopathic changes, variation in fibre size, rounding, central nuclei, and increase in connective tissue occurring in various anterior horn cell disorders are seen not to be specific `myopathic'' changes. Thus there was an overlap of pathological reactions in muscles from the dystrophies and the neurogenic atrophies. Comparably atrophied fibres (much less than 2 SDs below the normal mean diameter) and hypertrophied fibres (much more than 2 SDs above the normal mean diameter) were encountered in both dystrophy and neurogenic atrophy, considering the large muscles of the limb. Likewise, the mean fibre diameters were comparable in DMD and in juvenile SMA. The fourth evidence of a neurogenic factor in muscular dystrophy was derived from an examination of SDH preparations of muscle. There was a preponderance of type I muscle fibres in dystrophic muscles compared with specimens from controls, suggesting depletion of type II fibres. It appears that the concept of muscular dystrophy as a primary muscle disease needs to be re-examined.     

Laparoscopic Nissen fundoplication during gastrostomy tube placement and noninvasive ventilation may improve survival in type I and severe type II spinal muscular atrophy

Progressive respiratory muscle weakness with bulbar involvement is the main cause of morbidity and mortality in type I and severe type II spinal muscular atrophy. Noninvasive positive pressure ventilation techniques coupled with laparoscopic gastrointestinal procedures may allow for improved morbidity and mortality. The authors present a series of 7 spinal muscular atrophy patients (6 type I and 1 severe type II) who successfully underwent laparoscopic gastrostomy tube insertion coupled with Nissen fundoplication and early postoperative extubation using noninvasive positive pressure ventilation techniques. The authors measured the length of survival and the frequencies of pneumonia and hospitalization before and after surgery as outcomes of these new surgical and medical interventions. All 7 patients had respiratory symptoms (unmanageable oropharyngeal secretions, cough, pneumonia), difficulty feeding, and weight loss. Six patients had documented reflux via diagnostic testing preoperatively. Five patients were on noninvasive positive pressure ventilation and other supportive respiratory therapies prior to surgery. All 7 patients survived the procedures. By August 2006, 5 patients with type I and 1 with severe type II spinal muscular atrophy were alive and medically stable at home 1.5 months to 41 months post-op. One patient with type I expired approximately 5 months post-op due to obstructive apnea. This case series demonstrates that laparoscopic gastrostomy tube placement coupled with Nissen fundoplication and noninvasive positive pressure ventilation can be successfully used as a treatment option to allow for early postoperative extubation and to optimize quality of life in type I and severe type II spinal muscular atrophy patients.     

Muscular hypertrophy in denervation: report of 2 cases with a histochemical and histometric study of normal and hypertrophic muscles

Report of two adult males, 31 and 24 years-old, with hypertrophy in their left inferior limb, with denervation in the electromyography. Both patients undergone to a muscle biopsy in the normal and in the enlarged limb, which were processed by histochemistry. The mean muscle fiber diameter, percentage of muscle type fibers and atrophy and hypertrophy factors were calculated, as well as histographic fiber analysis. We found rare atrophic muscle fibers and one of the patients had hypertrophy of type II muscle fiber and the other hypertrophy of both types. The calculation of the atrophy and hypertrophy factors, revealed a predominance of type II fiber hypertrophy in both quadriceps of the two patients and type I hypertrophy in one case. A discussion about the factor responsible by the hypertrophy in denervation is made. The possible etiology of one case was a S1 radiculopathy and in the other, a possible motor neuron disease.     

Possible pathogenic role of muscle cell dysfunction in motor neuron death in spinal muscular atrophy

We have previously shown that myofibers formed by fusion of muscle satellite cells from spinal muscular atrophy (SMA) I or II undergo degeneration 1 to 3 weeks after innervation by rat embryonic spinal cord explants, whereas normal myofibers survive for several months. In the "muscle component" of the coculture, the only cells responsible for the degeneration are the SMA muscle satellite cells. Moreover, SMA muscle satellite cells do not fuse as rapidly as do normal muscle satellite cells. To determine whether death of muscle cells precedes that of motor neurons, we studied the origin and kinetics of release of apoptotic microparticles. In SMA cocultures, motor neuron apoptosis occurred before myofiber degeneration becomes visible, indicating that SMA myofibers were unable to sustain survival of motor neurons. In normal cocultures, motor neuron apoptosis occurred 4 days after innervation. However, it did not continue beyond 2 days. These results strengthen the hypothesis that SMA is due to a defect in neurotrophic muscle cell function.     

Neonatal spinal muscular atrophy with multiple contractures,bone fractures,respiratory insufficiency and 5q13 deletion

We present the case of a floppy neonate with marked and generalized weakness, respiratory insufficiency and fetal akinesia deformation sequence. The infant showed multiple joint contractures, two bone fractures and needed mechanical ventilation from birth to death at 16 days of age. Electrophysiological assessment showed electrically unexcitable motor and sensory nerves. Muscle biopsy showed diffuse atrophy of type I and type II fibers. Necropsy confirmed the diagnosis of infantile spinal muscular atrophy (SMA) with severe loss of motor neurons in anterior horns and motor nuclei of brainstem. There were also neuronal loss, gliosis, chromatolysis, ballooned cells, empty cell beds and neuronophagia figures in other brainstem and brain nuclei. Genetic analysis of the patient revealed homozygous deletions of survival motor neuron gene 1 (SMN1) and a single copy of SMN2 in region 5q13. This case confirms that the loss of spinal motor neurons underlies the muscular atrophy in severe cases of 5q SMA. This case also shows that the presence of multiple joint contractures, bone fractures and respiratory insufficiency in SMA in the neonatal period does not necessarily exclude the occurrence of classical deletions in the SMA 5q13 region. Rather, these atypical clinical findings show the extreme severity and prenatal onset of the disease in these SMA cases, which may be related with the occurrence of a single copy of SMN2 gene. More reports of clinically, pathologically and genetically well-documented cases are essential to define the different types of this disease.     

Opsoclonus-myoclonus syndrome associated with Mycoplasma pneumoniae infection in an elderly patient

Neurogenic muscle hypertrophy is very unusual and has been rarely described. We described a 25-year-old woman presented with proximal muscle weakness with calf muscle hypertrophy. Limb magnetic resonance imaging scans showed increased muscle bulk without fatty changes, and a muscle biopsy revealed prominent hypertrophic type II muscle fibers. A mutation in SMN1 was found in a genetic analysis. This is the first report of neurogenic muscle hypertrophy seen in genetically confirmed spinal muscular atrophy III.     

Predictive value of electromyography in diagnosis and prognosis of the hypotonic infant.

To investigate the diagnostic validity of electromyography in the hypotonic infant, 79 children aged 0 to 12 months, seen over a 20-year period, were studied retrospectively. The diagnoses using clinical, muscle biopsy, and laboratory characteristics were: 25 central hypotonia, 20 spinal muscular atrophy, 20 myopathy, four myotonic dystrophy, four benign congenital hypotonia, two congenital muscular dystrophy, two myasthenia gravis, one infantile inflammatory myopathy, and one arthrogryposis multiplex congenita. Using strict criteria, electromyography accurately predicted the final diagnosis in 65% of infants with spinal muscular atrophy and was consistent with the diagnosis in another 25%. In contrast, electromyography accurately predicted the final diagnosis in only 10% of infants with myopathy and was normal in 88% of infants with central hypotonia. In infants with spinal muscular atrophy, there was no difference in the predictive value of electromyography when performed in the newborn compared to older infants. Normal distal nerve conduction velocities in infants with spinal muscular atrophy may predict prognosis, since these infants had a longer survival. Electromyography thus has a high predictive value for infantile spinal muscular atrophy but not for myopathy.     

Metachromatic leukodystrophy: report of 2 cases with histochemistry of nerves and muscles

Two cases of metachromatic leukodystrophy, of the late infantile form are reported. The patients were a girl and a boy of 2 years 10 months old, with initial normal development, but by the age of 18 months began with gait disturbances, difficulty to speak and developed progressive mental deterioration, with signs of long tract involvement, absence of deep tendon reflexes, spasticity, blindness, muscle atrophy and finished in a vegetative state. The diagnosis was made electromyography (signs of denervation), motor nerve conduction velocity (very decreased), assay of arylsulfatase A in the urine (absence of activity), sural nerve biopsy (demyelination and presence of metachromatic granules by the cresyl-violet and toluidine blue) and muscle biopsy (atrophy of type I fibers and presence of metachromatic material in the intramuscular nerve fibers). A quick revision about diagnostic methods, transmission, pathogenesis and variant forms is made.     

Is childhood schizophrenia a cholinergic disease? I. Muscle morphology

Four hypotonic boys (aged 4 years and 11 months, 6 years and 9 months, 7 years and 4 months, and 8 years and 10 months, respectively), all of whom demonstrated a formal thought disorder, had been psychotic for more than six months, and met the DSM-III criteria for chronic undifferentiated schizophrenia, were studied with respect to skeletal muscle morphology. A significant difference between the mean fiber diameters of type I and type II muscle fibers was observed in the three boys with the most severe thought disorder, type II muscle fibers being consistently smaller. No significant difference in the mean fiber diameter between the two fiber types were seen in the fourth boy, who was also the only one who demonstrated any secondary thought process. The boys differed in their activity levels, but there was no correlation between type II muscle fiber atrophy and hypoactivity. It is hypothesized that a depressed cholinergic system is implicated in the pathogenesis of both the muscle fiber atrophy and the formal thought disorder.     

Type I spinal muscular atrophy can mimic sensory-motor axonal neuropathy

Spinal muscular atrophy is a group of allelic autosomal recessive disorders characterized by progressive motoneuron loss, symmetric weakness, and skeletal muscle atrophy. It is traditionally considered a pure lower motoneuron disorder, for which a current definitive diagnosis is now possible by molecular genetic testing. We report two newborns with a clinical phenotype consistent with that of spinal muscular atrophy type I and nerve conduction studies and electromyography suggesting more extensive sensory involvement than classically described with spinal muscular atrophy. Molecular testing confirmed spinal muscular atrophy in patient 1 but not in patient 2. Thus, in the setting of a suspected congenital axonal neuropathy, molecular testing might be necessary to distinguish spinal muscular atrophy type I from infantile polyneuropathy.