TOACS FCPS Station · Abnormal Movements in Dystonia

📷 Clinical Photograph – Dystonia Posture

Clinical photograph showing sustained abnormal posture with twisting movements characteristic of dystonia

Figure 1 · Dystonia · Abnormal movement disorder

🔍 Key clinical features:

✓ Sustained muscle contractions – leading to twisting and repetitive movements
✓ Abnormal postures – often painful and progressive
✓ May be focal, segmental, or generalized – involvement of one or multiple body regions
✓ Worsened with action – often task-specific (e.g., writer's cramp)
✓ Diurnal variation – symptoms worse at end of day (dopa-responsive dystonia)

📋 Clinical scenario (examiner prompt)

A 7‑year‑old girl is brought to the neurology clinic with a progressive gait abnormality that started in the left foot and has now spread to her leg and trunk over the past 6 months. The movements are worse in the evening and improve after a nap. On examination, the child has dystonic posturing of the left leg, foot inversion, and truncal twisting that is exacerbated by walking. There is no weakness or sensory loss. The child has a normal MRI brain.

Progressive gait abnormality Diurnal variation (worse evening) Dystonic posturing, foot inversion Normal brain MRI

🧑‍⚕️ Examiner tasks · TOACS

1. Identify the diagnosis from the clinical image and context.

2. Describe the clinical features (dystonic posturing, diurnal variation, progression, gait abnormality).

3. Explain the underlying condition (dopa-responsive dystonia, DYT5, GCH1 mutation).

4. Discuss diagnosis and management (levodopa trial, response, genetic testing, treatment).

⚠️ Key concept: Dopa-responsive dystonia (DYT5, Segawa syndrome) is a treatable cause of childhood-onset dystonia. It is caused by GCH1 mutations → tetrahydrobiopterin (BH4) deficiency → dopamine deficiency. Key features: childhood onset, diurnal variation (worse evening, improves with sleep), progressive dystonia starting in a limb, and dramatic response to low-dose levodopa. A trial of levodopa is mandatory in all children with dystonia. Trihexyphenidyl and DBS are options for refractory cases.

🎯 Expected answers (for examiners)

• Diagnosis: Dopa-responsive dystonia (DYT5, Segawa syndrome)
• Clinical features: Childhood onset (typically 4-8 years); dystonia starting in a lower limb (gait abnormality, foot inversion); diurnal fluctuation (worse at end of day, improves with sleep); progressive to generalized dystonia; normal cognition; normal brain MRI
• Genetics: GCH1 mutation (autosomal dominant, GTP cyclohydrolase 1 deficiency) → BH4 deficiency → dopamine deficiency; also THAP1 (DYT6), TOR1A (DYT1)
• Diagnostic test: Trial of carbidopa-levodopa (1-2 mg/kg/day) – dramatic and sustained response confirms; genetic testing for GCH1
• Treatment: Carbidopa-levodopa (dose titrated to response); trihexyphenidyl for adjunctive; DBS for refractory generalized dystonia

📌 Dopa-responsive dystonia (DYT5) – key points:
• Onset: Childhood (4-8 years), often lower limb
• Diurnal variation: Worse evening, improves with sleep
• Dramatic response to levodopa – low doses (1-2 mg/kg/day)
• Gene: GCH1 (GTP cyclohydrolase 1)
• Mechanism: BH4 deficiency → dopamine deficiency
• Must be ruled out in all childhood dystonia

⚡ Quick FCPS‑style MCQ

A 7-year-old with progressive dystonia starting in the left foot, worse in the evening, and improving with sleep. The most appropriate next step is:

A. Deep brain stimulation B. Trial of carbidopa-levodopa C. Botulinum toxin injections D. Trihexyphenidyl

🎯 TOACS FCPS Station · Abnormal Movements in Dystonia

📷 Clinical Photograph – Dystonia Posture

🧑‍⚕️ Examiner tasks · TOACS

📌 Topic summary · Abnormal Movements in Dystonia

Feature	Dopa-Responsive Dystonia (DYT5)	DYT1 Dystonia
Gene	GCH1	TOR1A
Onset	Childhood (4-8 years)	Childhood (leg often first)
Diurnal variation	Yes (worse evening)	No
Response to levodopa	Dramatic (low dose)	No
Treatment	Carbidopa-levodopa	Trihexyphenidyl, DBS