Muscle Rigidity, Stiffness, Painful Spasms
The symptoms of classic SPS are muscle rigidity, stiffness, and painful spasms in muscles of the trunk, including the back, and limbs. The muscle spasms and stiffness are highly variable in their severity and rate of worsening.
Non-linear Symptom Progression
In the early stages of SPS, symptoms of waxing and waning back stiffness may be subtle. Both the spasms and the stiffness can fluctuate a lot on a day-to-day basis and over months and years. The stiffness and rigidity do not necessarily progress at the same rate or intensity as the muscle spasms. There can be periods when the symptoms seem stable and other times when the worsening is more noticeable and rapid. However, for most people there is worsening of stiffness and muscle spasms over the long term. The muscle spasms may be brief, lasting minutes, though at other times can last hours or days and cause severe pain. The fluctuations may be influenced by medications, activity and other interventions.