Spasticity, dystonia and tone management: Viva

Branch 1: Classifying the tone

A strong candidate starts with the phenotype, because the phenotype drives the drug. This child has spasticity: a velocity-dependent increase in tonic stretch reflexes, felt as a catch then a release, distinct from dystonia, which is an action and overflow driven twisting posture that vanishes in sleep. The candidate names the Sanger framework as the international standard, confirms the velocity-dependent pattern with the Modified Tardieu Scale, and states the GMFCS level of two, which frames the functional goal and the modality, since GMFCS one to three is the orthoses, botulinum toxin and rhizotomy candidate. [1]

Branch 2: Goals and the first-line modality

When the examiner asks how the candidate chooses the therapy, the answer is the goal-directed principle: tone is treated only when it limits function, comfort, care or participation. This child's adductor spasticity limits care and hygiene and her calf spasticity limits gait, so both are legitimate targets. The first-line modality is focal botulinum toxin type A into the overactive adductors and gastrocnemius-soleus, layered on a daily stretching program, an ankle-foot orthosis and serial casting. The candidate sets SMART goals with the family using Goal Attainment Scaling and books a reassessment at four to six weeks. [1][5]

Branch 3: Botulinum toxin dosing and timing

The candidate is expected to know the toxin cold. The three products, onabotulinumtoxinA, abobotulinumtoxinA and incobotulinumtoxinA, are not interchangeable and their units must never be converted between brands. The onset is two to seven days, the peak is around four weeks and the duration is twelve to sixteen weeks, and the minimum re-injection interval is twelve weeks to limit neutralising antibody formation. The total per-session onabotulinumtoxinA dose is individualised, commonly up to around fifteen to twenty units per kilogram with a per-child ceiling near four hundred units. The toxin blocks acetylcholine at the neuromuscular junction for a focal effect, distinct from baclofen, which is a GABA-B agonist at the spinal cord. [1][5]

Branch 4: Selective dorsal rhizotomy

The examiner then offers selective dorsal rhizotomy as a definitive option, and the candidate explains why this child fits and what the evidence shows. The operation section a proportion of the L2 to S1 dorsal rootlets, often around twenty-five to sixty-seven percent, to remove the sensory afferent input that drives the spasticity in the legs, and it suits the GMFCS two or three spastic diplegic child with good selective control and minimal dystonia. The McLaughlin meta-analysis of three randomised trials showed it with therapy outperformed therapy alone for spastic diplegia in younger children, and the long-term data confirm a durable reduction in spasticity and later orthopaedic surgery. The candidate stresses that loss of spasticity is not the same as a gain in function, that the operation unmasks weakness, and that the family must commit to months of intensive physiotherapy and strengthening. [6]

Branch 5: The intrathecal baclofen withdrawal emergency

The examiner pivots to a different child with an intrathecal baclofen pump whose infusion has failed, and the candidate must treat it as an emergency. Abrupt withdrawal of intrathecal baclofen drives rebound spasticity, high fever, rigidity, seizures, rhabdomyolysis and progression to multi-organ failure and death. The candidate restores the infusion as soon as possible, gives high-dose enteral baclofen, adds a benzodiazepine such as diazepam or lorazepam for the rigidity and seizures, cools the fever and admits to intensive care, treating on suspicion rather than waiting for confirmation. The candidate contrasts this with intrathecal baclofen overdose, which presents with hypotonia and respiratory depression and is managed by stopping the infusion and supporting the airway while the drug clears. [8][9]

Branch 6: The dystonia pathway

The examiner then offers a dystonia-dominant child, and the candidate explains why botulinum toxin and rhizotomy disappoint in pure dystonia. The pathway begins with the oral agents: trihexyphenidyl, an anticholinergic, is first-line in many centres despite limited Cochrane evidence, with the anticholinergic burden of dry mouth, constipation, urinary retention and blurred vision, and oral baclofen and clonazepam as alternatives. The severe generalised dystonic child who fails oral therapy is escalated to intrathecal baclofen or to globus pallidus internus deep brain stimulation, which can give dramatic relief in selected dystonic cerebral palsy. [11][12]

The examiner rewards a candidate who leads with the goal-directed principle, who separates the spastic from the dystonic phenotype with the Modified Tardieu Scale, who states the GMFCS, who knows the botulinum toxin products are not interchangeable and the twelve-week interval, who matches the rhizotomy to the well-selected diplegic child with the McLaughlin evidence, who treats the intrathecal baclofen withdrawal as an emergency, and who frames the lifelong multidisciplinary plan. [1][6]