Neurological Disorders: Spinal Muscular Atrophy

Introduction

Spinal Muscular Atrophy (SMA) is an autosomal recessive type of inherited degenerative neuromuscular disorder and is predominantly seen in infants & children. Patient will manifest with muscle weakness and muscle atrophy (thinning of muscle) however it is not a primary muscle disease, rather the muscle changes are secondary to the degeneration of the nerve cells (neurons) that control the muscles.

There are 3 types;

• Infantile
• Juvenile
• Adult types

The infantile type is the commonest and most rapidly progressive among all subtypes.

What causes it?

As mentioned above it is an AR (autosomal receive type) of genetic disorder. It means both parents must be carrying the genetic mutation for a child to get this disease. Every child has 25% chance of contracting the disease.

In this disease there is degeneration of the motor neurons in the spinal cord (anterior horn cells). These neurons control the muscle tone, strength and its movements. As these neurons degenerate the muscles supplied by these neurons will start manifesting with various neurological manifestations related with muscle dysfunction.

What are the clinical manifestations?

Progressive skeletal muscle weakness is the main feature of this disease. Delayed motor milestones and or regression of previously acquired milestones is seen. At a later stage respiratory (breathing muscle) paralysis threatens the life. Because of the decreased muscle tone the infants appear floppy (floppy baby syndrome).

Mental abilities are expected to be normal in the typical cases. Sensory system is also not affected.

Diagnosis

A genetic (DNA) test can identify the mutation and confirm the diagnosis.

Few other tests that may also be employed and include;

• EMG/NCS (electromyography & nerve conduction studies)
• Muscle biopsy
• Blood tests like CPK (elevated mostly in cases of myopathies, either normal or minimally elevated I these patents)

EMG and muscle biopsies show findings suggestive of neurogenic changes.

Management

There is no cure for this condition at this moment so the management is supportive & symptomatic. Physical therapy, assistive devices like braces, wheel chairs, and orthopedic surgeries are needed for these patients especially at the later stages in the illness.

A pediatric and/or adult neurologist is commonly involved in the treatment of SMA (Spinal muscular Atrophy) patients.

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