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Published on: March 4, 2014
Benign infantile neurogenic muscle atrophy predominantly involving the upper extremities
Naoto Yamada1, Toshiro Nagai, Keiko Shikura
1Department of Pediatrics, Ryokuseikai-Seiikuen Hospital for Severe Motor and Intellectual Disabilities, 2-35-1 Ogawanishi-machi, Kodaira, Tokyo 187-8585, Japan. nyam@sannet.ne.jp
Insights
This study presents a case of a young girl with hypotonia and muscle weakness, initially suspected to be a neurogenic disorder. Findings suggest abnormal skeletal muscle innervation rather than a degenerative condition.
Area of Science:
- Neurology
- Pediatrics
- Muscle Diseases
Background:
- A case study of an infant presenting with hypotonia and developmental delay.
- Initial assessment suggested a potential neurogenic disorder affecting motor function.
Observation:
- Muscle biopsy revealed atrophic fibers and fiber type grouping, but intact myelination.
- The patient showed improvement over time, achieving motor milestones like walking.
- Clinical presentation included progressive muscle weakness and mild scoliosis.
Findings:
- Electromyography (EMG) results were not indicative of a neurogenic disorder.
- Genetic testing for the survival motor neuron (SMN) gene was negative.
- The condition is hypothesized to stem from abnormal skeletal muscle innervation.
Implications:
- This case challenges typical diagnostic pathways for pediatric hypotonia.
- Suggests considering anterior horn cell dysgenesis or anomalous peripheral nerve branching.
- Highlights the importance of comprehensive diagnostic approaches in pediatric neuromuscular disorders.
Abstract:
An eight year-old girl was first noted to be hypotonic at 4 months of age. She had a delay in achieving developmental milestones and showed apparent weakness predominantly affecting muscles of the upper extremities. In the left biceps brachii muscle biopsy at the age of 5 months, there were groups of atrophic fibers and marked fiber type grouping, but intramuscular nerves were well myelinated and there were few type 2C fibers. She improved with age and learned to walk at 1 year and 4 months and had minimal weakness of the forearm muscles and mild atrophy of the muscles of the right upper extremity. She recently developed a mild scoliosis. Since the EMG was not neurogenic and no mutations were found in the survival motor neuron (SMN) gene, we believe that she does not have a degenerative neurogenic disorder but rather has an abnormal innervation of the skeletal muscles due either to anterior horn cell dysgenesis or anomalous peripheral nerve branching.
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