Focally active medications are for specialist use in conjunction with physical treatments (e.g. splints).
1) Botulinum Neurotoxin (BoNTx) Injection:
- Genetically engineered toxin derived from clostridium botulinum, a bacterium which causes botulism, a disease manifest by muscle paralysis.
- It works by blocking presynaptic cholinergic nerve terminals.
- Advantage in use is to target affected muscles, sometimes with the added benefit of augmenting effectiveness of antagonist muscles.
- Treatment effect lasts 3 to 4 months, the time required for neural pathways to develop a new neuromuscular junction through new axonal sprouting.
- Repeat injection at 3 to 4 monthly intervals are required. Tolerance may develop over time and reduce effectiveness.
- Treatment may be ineffective. Reasons for this may include:
- Inappropriate use in contracted rather than spastic muscle.
- Poor muscle localisation. Electromyography (EMG) or ultrasound guidance is strongly recommended to improve localisation.
- Insufficient dose.
- Development of tolerance.
- Potential side effects include:
- Paresis of injected muscle.
- Paresis of adjacent muscles.
- Local pain or haematoma.
2) Other Focal Treatment Options including:
a. Phenol injection/motor nerve block:
- Similar advantages to botulinum toxin in terms of local versus systemic effect.
- But its use is limited for the following reasons:
- Its use is only applicable in nerves that have predominantly motor (vs sensory) roles and in nerves which are easily accessible (typically tibial or obturator nerves or lumbar spinal cord).
- It requires specialist expertise which is not widely available.
b. Intrathecal Baclofen Pump:
- Useful when:
- Spasticity is predominantly in lower limbs.
- Complete loss of function in lower limbs is pre-existing and accepted.
- All other treatment options have failed.
- Principal risk arises from:
- Administration errors or failures can lead to abrupt withdrawal or overdose syndromes.
- Respiratory depression or central sedation if Baclofen disperses to cervico-thoracic regions.