Dystonia in PSP: Subtype Patterns and MRI Associations

Key Takeaways

• Dystonia was common among clinically classified patients with progressive supranuclear palsy at a movement-disorders clinic in India.
• Limb dystonia was prominent in PSP-CBS, whereas cranio-cervical involvement predominated in PSP-RS.
• Lower midbrain-to-pons ratios and higher MRPI were associated with dystonia, without establishing causation or independent prediction.
• Apparent earlier dystonia in PSP-CBS did not reach statistical significance.
• Among selected botulinum toxin recipients, 63.2% had marked and 36.8% partial improvement; these observations do not establish treatment efficacy.

Investigators recruited 88 consecutive patients into a prospective PSP cohort at a single movement-disorders clinic in Faridabad, India during 2024–2025. Two movement disorder specialists performed one-time assessments using 2017 Movement Disorder Society (MDS) criteria. Although eligibility wording specifies possible or probable PSP, the Methods and Results also include patients meeting MDS criteria for suggestive PSP. Investigators recorded dystonia presence, site, and onset timing at a single assessment, and assessed magnetic resonance imaging (MRI) midbrain-to-pons ratio, magnetic resonance parkinsonism index (MRPI), and cortical atrophy. They made unadjusted comparisons between patients with and without dystonia and across major clinical phenotypes.

Dystonia affected 57 of 88 patients with PSP (64.8%), appearing as isolated limb involvement, isolated cranio-cervical involvement, or both. Limb dystonia affected 18 of 21 patients with PSP–corticobasal syndrome (PSP-CBS; 85.7%), predominantly in the upper limb at onset. Cranio-cervical involvement predominated in PSP–Richardson syndrome (PSP-RS), and dystonia patterns differed significantly across phenotypes. Dystonia-onset latency and the proportion with early onset, defined as within the first year, did not differ significantly across major subtypes. In their separate literature synthesis, Gulati and Pandey estimated previously reported dystonia frequency at approximately 30–60%.

The unadjusted MRI comparison showed a mean midbrain-to-pons ratio of 0.22 ± 0.08 with dystonia versus 0.27 ± 0.07 without dystonia (p = 0.005). MRPI was also higher in the dystonia group (17.7 ± 4.5 vs 14.4 ± 2.6; p = 0.003). Because PSP-RS, the subtype with the lowest midbrain-to-pons ratio, was overrepresented among patients with dystonia, subtype mix may contribute to these differences. Neither association demonstrates that imaging changes caused dystonia. Separately, 19 selected patients with disabling dystonia received ultrasound-guided botulinum toxin. Follow-up combined physician assessment with patient reports of stiffness and pain: 12 had marked improvement, 7 had partial improvement, and none reported worsening.

Clinical classifications lacked pathological confirmation. Patients were assessed once at a single center, which precluded longitudinal observation of dystonia. Very small subtype groups were excluded from inferential tests, and validated scales did not quantify dystonia severity, functional impact, or injection response. MRI comparisons were unadjusted and injection observations uncontrolled. Response duration was not specified, and systematic adverse-event assessment was not described. These features limit what the imaging associations and reported injection responses can establish.

Clinician Questions

Can dystonia be the presenting feature of PSP-corticobasal syndrome?

Yes. Dystonia was the presenting feature in 5 patients with clinically classified progressive supranuclear palsy, 4 of whom had the PSP-CBS phenotype. Onset timing was recorded at a single assessment rather than through prospective observation of symptom evolution.

Which craniofacial dystonia patterns were observed in progressive supranuclear palsy?

Among patients with clinically classified progressive supranuclear palsy and cranio-cervical dystonia, investigators observed blepharospasm, facial dystonia, and orolingual dystonia. Some patients had overlapping manifestations, so these categories were not mutually exclusive.

What parietal MRI finding accompanied dystonia in PSP-corticobasal syndrome?

In 11 of 21 patients clinically classified with PSP-CBS, parietal cortical atrophy appeared opposite the side of dystonia. Only 18 of these 21 patients had dystonia, but the source reports the finding against all 21. This cortical observation differs from the group-level brainstem-marker comparison and does not establish a causal mechanism.