Objective: To build a platform in order to investigate the clinical spectrum of stiff person syndrome and related disorders, and to explore possible gaps in management and areas for further research.

Background: Stiff person syndrome and related disorders (stiff person spectrum disorders, SPSD) are a very rare group of autoimmune movement disorders with an estimated prevalence of 1/1 000 000. Whereas the classical variant is associated with GAD-antibodies and manifests with predominant lumbar stiffness, the clinical and serological spectrum has broadened to include a wider range of phenotypes and antibodies.

Methods: The survey started in 03/2018 and is conducted amongst the members of the MDS rare movement disorders study group.

Results: The survey is ongoing and at the time of abstract submission we report the first preliminary results. So far, 16 patients from 3 centres (UK, Argentina, Spain) were included (9 female) with a follow up time of 10 years on average (range 2-28). Median age of onset was 52.5yrs (range 29-68). Most patients (68,8%) had focal stiffness at onset and manifested with (painful) cramps (62.5%), axial stiffness (56,3%). Cerebellar signs (nystagmus, ataxia) or bulbar involvement occurred in 18.8%, respectively. 12.5% of patients displayed myoclonus at presentation, whereas prominent autonomic signs or epilepsy were rare (6,3% and none). Most of the patients harboured GAD-antibodies (93.8%), and concomitant autoimmunity was frequent (56.3%). Two cases were possibly paraneoplastic, as neurological symptoms occurred in close temporal relationship with cancers (oral squamous cell carcinoma, nasopharyngeal). Treatment approaches and outcomes were similar across the different centres. All but 1 patient received immunotherapy, most frequently intravenous immunoglobulins (87.5%) and plasma exchange (43,8%). Other immunotherapies used were steroids and rituximab (12.5% each), and azathioprine (6.3%). In 50%, a combination of at least two immunotherapy approaches was required. With treatment, half of the cases improved and a third remained stable.

Conclusions: This is the first international multicentre SPSD study with prospective data collection by movement disorder experts. Further plans include expanding this cohort and, using a health services approach, identifying unmet needs in SPSD and areas for further research.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/an-international-survey-of-stiff-person-spectrum-disorders-exploring-the-clinical-spectrum-and-unmet-needs/