How is SMA diagnosed?
Diagnosing Type 1 and Type 2 SMA generally begins with an exam by a pediatric neurologist. The neurologist looks for the following physical characteristics: • Rag doll-like appearance • “Frog” shaped legs with the knees apart and legs bent • Poor posture and limited mobility • Sunken or narrow chest • Big belly • Breathing with the belly instead of the lungs • Weak cry and weak cough • Poor to no head/neck control • Weak movement of the legs and/or arms • Inability to bear weight on legs or arms • Clenched hands or hands turned the wrong way • Difficulty with sucking and swallowing • Tongue fasciculations (tongue vibrating rapidly) Approximately 95% of SMA cases can be confirmed through a blood test that looks for the absence or mutation of spinal motor neuron genes. These genes are responsible for producing proteins that the muscles use to move. If the blood test is not able to confirm SMA, neurologists usually recommend an EMG (electromyography) test. This test measures the electrica
Medical experts believe that a blood test screening for the deletion of the gene called Survival Motor Neuron (SMN) can typically diagnose SMA. If symptoms are exhibited and there is no indication of gene deletion, a muscle biopsy and/or Electromyography (EMG) may be necessary to confirm the diagnosis.
The first steps in diagnosis of a neuromuscular disease are usually an in-office physical examination and family history, with some nonpainful tests to distinguish SMA from similar conditions (such as muscular dystrophy). The doctor may order a simple blood test for an enzyme called creatine kinase (CK). This enzyme leaks out of muscles that are deteriorating. It’s a nonspecific test, since CK levels are elevated in many neuromuscular diseases, but it’s often useful anyway. High blood CK levels aren’t harmful; they’re just an indicator of muscle damage.
