Dopa responsive dystonia due to a GCH1 gene variant mimicking hereditary spastic paraparesis.

Background: Dopa-responsive dystonia (DRD) is a group of rare forms of genetically determined dystonia. Large improvements of symptoms can be seen with small doses of levodopa. As a treatable condition, it must be diagnosed and treated to improve the patients' functional outcome and quality of life.

Case presentation: We describe the case of a woman affected by progressive gait impairment and lower limb rigidity, started at the age of 15. For talipes equinovarus (clubfoot), she underwent Achilles tendon lengthening and anterior tibial haemitendon transposition surgery. Family history collection revealed that her mother had been diagnosed with spastic paraparesis in adolescence. Clinical phenotype and family history suggested a diagnosis of hereditary spastic paraparesis (HSP), supported by a mild involvement of the pyramidal tract in lower limbs at the motor evoked potential. Clinical evaluation revealed the presence of mild signs of dystonia, as a foot and cervical dystonia and upper limbs dystonic tremor. Indeed, a virtual panel for dystonia genes showed a pathogenic splice-site variant in GCH1. The patient was diagnosed with DRD and low doses of levodopa were started with clinical improvement of both gait and dystonia.

Conclusion: We describe the clinical history of a patient with dopa responsive dystonia, which was initially diagnosed with HSP. Misdiagnosis can result in a significant delay in diagnosis and treatment initiation, so it is of the utmost importance to identify these patients without delay, looking for the presence of soft dystonia signs and performing an empirical trial with low doses of levodopa.