SPS is a rare condition and not well understood.
According to the National Institute for Neurological Disorders, it is characterised by fluctuating muscle rigidity in the trunk and limbs and a heightened sensitivity to stimuli such as noise, touch, and emotional distress, which can set off muscle spasms.
Abnormal postures, often hunched over and stiffened, are characteristic of the disorder, the institute says.
People with SPS can be too disabled to walk or move, or they are afraid to leave the house because street noises, such as the sound of a horn, can trigger spasms and falls.
Most individuals with SPS have frequent falls and because they lack the normal defensive reflexes; injuries can be severe.
While there is no cure for SPS, there are treatments - including anti-anxiety medicines and muscle relaxants - which can slow down its progression.
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