that are triggered by sudden movements as well as feeling upset or startled. Spasms are sometimes accompanied by elevated blood pressure, heart rate, body temperature, and sweating. Some experience chronic muscle pain. The muscle stiffness initially fluctuates, sometimes for days or weeks, but eventually begins to consistently impair mobility. As the disease progresses, patients sometimes become unable to walk or bend. Chronic pain is common and worsens over time, but sometimes acute pain occurs as well. Stress, cold weather, and infections lead to an increase in symptoms, and sleep decreases them. SPS patients experience superimposed spasms and extreme sensitivity to touch and sound. These spasms primarily occur in the proximal limb and axial muscles. Spasms usually last for minutes and can recur over hours. Attacks of spasms are unpredictable and are often caused by fast movements, emotional distress, or sudden sounds or touches. In rare cases, facial muscles, hands, feet, and the chest can be affected and unusual eye movements and vertigo occur. There are brisk stretch reflexes and clonus occurs in patients. Late in the disease's progression, hypnagogic myoclonus can occur. In addition to their physical symptoms, many with SPS experience neurological and psychiatric disorders. Some with SPS have various neurological disorders that affect physical reflexes, and the movement of the eyes. Some also experience anxiety, depression, alcohol use disorders, and phobias – particularly agoraphobia. Most patients are psychologically normal and respond reasonably to their situations. A minority of people with SPS experience "partial" SPS, also called "stiff limb syndrome", where the muscle contractions and stiffness are limited to the limbs, or sometimes a single limb. This syndrome develops into full SPS about 25% of the time. The stiffness begins in one limb and remains most prominent there. Sphincter and brainstem issues often occur with stiff-limb syndrome. Progressive encephalomyelitis with rigidity and myoclonus, another variant of the condition, includes symptoms of SPS with brainstem issues, autonomic disturbances, and myoclonus. In some cases, the limbic system is affected as well. Most patients have upper motor neuron issues and autonomic disturbances. Around 5% of those with SPS experience the symptoms as a paraneoplastic syndrome – a result of a tumor elsewhere in the body releasing bioactive molecules. Paraneoplastic SPS can affect either a single limb, or the trunk and limbs together. Causes Patients with SPS generally have high glutamic acid decarboxylase (GAD) antibody levels in their blood. About 80 percent of