Objective:

Characterize late-onset stiff person syndrome spectrum disorders (LO-SPSD).  

Background:

Most patients with SPSD experience symptom onset younger than age 50, but some develop symptoms later in life. Limited data exist regarding the clinical features and disability in LO-SPSD.

Design/Methods:

An observational study of SPSD patients seen in a tertiary referral clinic from 1997 to 2025 was performed. Demographics, clinical features, time to diagnosis and ambulation measures were collected.  

Results:

There were 90 patients with symptom onset >50-years-old. Most were female (76%), and white was the most common race (70%) followed by Black (22%). Mean age at diagnosis was 60.2 (SD=7.5), with a median time to diagnosis of 16.8 (IQR=8.2-29.6) months versus 48.6 (IQR=19.4-91.9) months for <50-years-old. Most patients were anti-GAD65-antibody positive (88%). Over half had a classic SPS phenotype (58%), followed by SPS-plus (21%). Misdiagnosis rate was 51% (versus 67% in those <50-years-old), with the most common initial incorrect diagnoses being vestibular dysfunction (27%), cervical spondylosis (20%), or dystonia (13%).  The most common initial symptoms were stiffness (50%), spasms (28%) and cerebellar/brainstem dysfunction (19%). At their first evaluation most (88%) patients >50-years-old reported gait difficulties and 60% needed a walking aid. The need for gait assistive device remained relatively stable over time, with 55% requiring one at last follow-up (compared to 37.5% at first visit and 36% at last visit in the <50-years-old group). 

Conclusions:

LO-SPSD had lower rates of misdiagnosis and shorter time to diagnosis than those under 50, however older patients had more gait difficulty, but this remained stable over time. Monitoring and counseling around ambulation safety is particularly important in an aging SPSD population.