Neurochemical reduction of spasticity

1. How are local anesthetics used in the treatment of spasticity?
2. How do chemical neurolytic agents work? How long are they effective for?
3. What are the side effects of phenol injections?
4. How does botulinum toxin work? What are its approved uses?
5. What is the usual dosing? How long is it effective for?
6. What are contraindications to receiving botulinum toxin?
7. What are common side effects of botulinum toxin?

Answers:
1. Local anesthetics like lidocaine or bupivacaine work by blocking the increase in permeability to Na ions normally associated with depolarization. It is used to determine the potential efficacy of a longer acting agent.
2. Chemical neurolytic agents like phenol or ethyl alcohol cause protein denaturation and axonal necrosis. They work from months to years.
3. Dysethesias (10-30%), muscle pain, muscle weakness, transient swelling, induration, DVT, sprains, skin slough, systemic reaction if injected intravascularly.
4. It produces denervation at the neuromuscular junction by blocking release of ACh. Approved uses include blepharospasm, strabismus, torticollis, and hemifacial spasm.
5. Dose is 25-200 units per muscle, maximum of 300-400 units per session, 3 months apart. Onset of action is usually 24-72 hrs after procedure but may take 7 days, peak is at 4-6 weeks, and it lasts 2-6 months.
6. Contraindications include sensitivity to botulinum, certain antibiotics (aminoglycosides, spectinomycin), myasthenia gravis, Lambert-Eaton syndrome, motor neuron disease, upper eyelid apraxia, pregnancy.
7. Side effects include weakness, hematoma, bruising, flu-like syndrome, dysphagia (from cervical injection), nerve trauma, local swelling, pain, local erythema, antibody formation.