What is spastic spinal paralysis (SSP), and how does it differ from ALS?

SSP is a rare motor neuron disease characterized by slowly progressive spasticity in the legs. It is caused by degeneration of motor neurons that extend from the brain to the spinal cord (upper motor neurons). The degeneration of the first motor neuron is a common feature shared with ALS: ALS can also lead to damage to the first motor neuron and the onset of spasticity. Unlike ALS, however, spasticity in SSP is largely confined to the lower extremities. Motor symptoms in the arms are either absent or minimal.

Other distinguishing features between SSP and ALS include the symmetrical onset of spasticity and a very slow rate of progression in SSP. ALS—including the specific subtype known as primary lateral sclerosis (PLS)—is characterized by an asymmetric onset of spasticity and rapid progression of motor symptoms. In SSP—unlike in ALS—approximately 50% of all affected individuals have a positive family history of the disease. In this context, SSP is also referred to as hereditary spastic paraparesis (HSP). In patients with HSP, mutations in specific genes can usually be detected through human genetic testing.