Intrathecal administration of drugs involves the implantation of a pump that delivers medication directly to the CNS. The benefit of this is that the drug remains in the spinal cord, without traveling in the bloodstream, and there are often fewer side effects. The most commonly used medication for this is baclofen but morphine sulfate and Fentanyl have been used as well, mainly for severe pain as a result of the spasticity. Injections Injections are focal treatments administered directly into the spastic muscle. Drugs used include: Botulinum toxin (BTX), phenol, alcohol, and lidocaine. Phenol and alcohol cause local muscle damage by denaturing protein, and thus relaxing the muscle. Botulinum toxin is a neurotoxin and it relaxes the muscle by preventing the release of a neurotransmitter (acetylcholine). Many studies have shown the benefits of BTX and it has also been demonstrated that repeat injections of BTX show unchanged effectiveness. Surgery Surgical treatment for spasticity includes lengthening or releasing of muscle and tendons, procedures involving bones, and also selective dorsal rhizotomy. Rhizotomy, usually reserved for severe spasticity, involves cutting selective sensory nerve roots, as they probably play a role in generating spasticity. Post-stroke pain syndromes Chronic pain syndromes are common in about one half of stroke patients. Central post-stroke pain (CPSP) is neuropathic pain which is caused by damage to the neurons in the brain (central nervous system), as the result of a vascular injury. One study found that up to 8% of people who have had a stroke will develop central post-stroke pain, and that the pain will be moderate to severe in 5% of those affected. The condition was formerly called "thalamic pain", because of the high incidence among those with damage to the thalamus or thalamic nuclei. Now known as CPSP, it is characterized by perceived pain from non-painful stimuli, such as temperature and light touch. This altered perception of stimuli, or allodynia, can be difficult to assess due to the fact that the pain can change daily in description and location, and can appear anywhere from months to years after the stroke. CPSP can also lead to a heightened central response to painful sensations, or hyperpathia. Affected persons may describe the pain as cramping, burning, crushing, shooting, pins and needles, and even bloating or urinary urgency. Both the variation and mechanism of pain in CPSP have made it difficult to treat. Several strategies have been employed by physicians, including