Signs and Symptoms of Spinal Muscle Atrophy

Spinal muscular atrophy, also known as SMA, is classified as a genetic condition and a type of motor neuron disease that impacts the nerve cells in the spinal cord. Lack of signals from these nerve cells (or motor neurons) causes muscle inactivity, or atrophy, to occur. The loss of nerve cells in this region of the nervous system are mainly responsible for muscle control and muscle movement.

A similar disease known as amyotrophic lateral sclerosis (ALS) or Lou Gehrig’s disease, which typically strikes in adulthood and also impacts neurons that control muscle movement, resulting in similar muscle weakness and loss of muscle movement throughout the body. Both ALS and SMA are considered fatal, eventually leading to a complete lack of muscle function in the chest, which causes respiratory failure.

Spinal muscular atrophy occurs in multiple forms (i.e., Chromosome 5 SMA in type 1 (Werdnig-Hoffman), type 2 (chronic infantile SMA), and type 3 (Kugelberg-Welander disease), or SMN-related SMA) and usually develops during birth, infancy, or during teenage years.

SMA symptoms can present similarly to ALS, with decreasing lack of muscle control as the main telltale symptom. However, even though all types of SMA progress at different rates and severity, these symptoms are often present:

  1. Development of weak fetal movements (in Type I SMA) during the final months of pregnancy.
  1. Chewing, feeding, and swallowing difficulties due to weakness in throat and mouth muscles.
  1. Hypotonia, or diminished muscle tone and signs of decreasing muscle weakness.
  1. Decreased strength and muscle movement in the chest, legs, shoulders, hips, thighs, upper back, and arms.
  1. Decreased reflexes (i.e., when a doctor taps the knee).
  2. Fasciculations, which are involuntary twitches and muscle contractions.
  1. Respiratory issues and recurrent respiratory infections (i.e., pneumonia).
  1. Difficulty sitting, walking, and standing independently.
  1. Orthopedic issues (i.e., kyphoscoliosis or curvature of the spine), which can progress to the need for wheelchair assistance.