Clinical presentation
The disease manifests exclusively with motor impairments, as the pathological process selectively affects the motor neurons of the anterior horns of the spinal cord.
Key manifestations include:
- Flaccid paresis. Muscle weakness is progressive in nature, eventually limiting the patient's motor capabilities.
- Muscle atrophy. Due to the loss of innervation, muscle tissue thins and loses its mass.
- Fasciculations. In affected muscles, involuntary twitching of individual muscle fiber bundles can be visually observed.
Important diagnostic marker: in spinal amyotrophies, sensory disturbances are absent. This helps differentiate them from other nervous system disorders affecting sensory pathways.
Classification criteria
Since spinal amyotrophies are a heterogeneous group of diseases, they are typically divided into various types. The distinctions between forms are based on the following criteria:
- Nature of the genetic defect and inheritance pattern. Determine the root cause of the pathology within a family.
- Age of onset. The onset can vary, which affects the severity of the clinical course.
- Localization of muscle weakness. Which specific muscle groups are involved first in the process.
- Rate of progression. The pace at which flaccid paresis and atrophies increase.
Diagnosis and treatment approaches
Confirming the diagnosis requires a comprehensive instrumental and laboratory approach.
- Electromyography (EMG): evaluates the electrical activity of muscles and confirms the neurogenic nature of the lesion.
- Muscle biopsy: reveals characteristic morphological changes in muscle fibers associated with denervation.
- Genetic laboratory testing: the gold standard for identifying a specific hereditary defect.
Therapy: Currently, there is no effective cure for spinal muscular atrophies. As a supportive measure, patients are prescribed regular therapeutic exercise aimed at slowing down atrophic processes and maintaining quality of life.
Briefly: answers to topical questions
What specific patterns are detected on needle EMG in spinal amyotrophies?
Needle electromyography registers characteristic features: a rarefied interference pattern, the appearance of various spontaneous activity potentials, and the formation of the so-called "picket fence rhythm". At rest, fibrillation potentials, positive sharp waves, and fasciculations are observed. Upon voluntary contraction, a small number of large-sized motor unit potentials are revealed with increased amplitude and duration.
What histological features are detected in muscle biopsies of patients with spinal amyotrophy?
Pathological examination of muscle tissue using immunohistochemical methods in atypical variants of spinal muscular atrophy reveals non-specific morphological features. These include group atrophy and fiber-type grouping of muscle fibers. Most of the hypertrophied muscle fibers belong to type I, all immunohistochemical markers remain normal, and ultrastructural changes are non-specific.
What types is proximal spinal muscular atrophy subdivided into depending on the age of onset?
The cited sources indicate that proximal spinal muscular atrophy is classified taking into account the age of disease onset. For type II SMA (chronic SMA, Dubowitz disease), onset typically occurs between 6 and 18 months of age.
Mutation of which gene causes the development of proximal spinal muscular atrophy?
The development of proximal spinal muscular atrophy is caused by mutations in the SMN1 gene (survival motor neuron protein), which is localized on chromosome 5 at locus 5q12.2-q13.3. The main type of mutation (in 95% of patients) is homozygous deletions of exons 7 or 7–8, while 5% of patients are compound heterozygotes.
What targeted pathogenetic therapies are used in current practice to treat spinal muscular atrophy?
In current clinical practice, the following medications are used for the pathogenetic therapy of spinal muscular atrophy:
- Nusinersen (Nusinersen) — an antisense oligonucleotide administered intrathecally.
- Risdiplam (Risdiplam) — a small-molecule drug for oral administration.
- Onasemnogene abeparvovec (Onasemnogene abeparvovec) — an adeno-associated viral vector-based gene therapy product for intravenous administration.
For the core picture of spinal amyotrophy, remember three elements: Heredity + Anterior horns (flaccid paresis and fasciculations) + NO sensory disturbances.
Class and exam questions
Is spinal muscular atrophy accompanied by decreased sensitivity?
No, this disease is characterized by isolated motor involvement. Sensory disturbances are not observed.
Which part of the spinal cord is affected in this pathology?
The substrate of the disease is the involvement of the anterior horn cells of the spinal cord.
Is there an effective etiopathogenetic treatment?
According to baseline data, there is no effective treatment. Therapeutic exercise remains the primary method for maintaining function.
What else to study on this topic
- Amyotrophic lateral sclerosis (ALS): differences from spinal amyotrophies
- Inflammatory myopathies: polymyositis and dermatomyositis
- Periodic paralyses: hypokalemic and hyperkalemic forms
- Technique and interpretation of EMG in neuromuscular disorders
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