Objective:

To assess the impact of stiff person syndrome spectrum disorders (SPSD) on the Nine-Hole Peg Test (9HPT) and Symbol Digit Modalities Test (SDMT).

Background:

SPSD are rare, neurological conditions primarily characterized by muscle rigidity and spasms, though other clinical features are increasingly recognized. Clinical measures are needed to assess different aspects of the disease, including upper limb and cognitive function. The 9HPT and SDMT are validated tools for assessing dexterity and information processing speed in other neurological populations. However, it is unclear whether these clinical tools may be useful in SPSD.

Design/Methods:

Demographic, clinical, and functional data (9HPT and SDMT) were collected from patients with SPSD from a specialized center between 2024-2025. Associations between test outcomes and demographics, such as age and SPS type, were examined using multivariate analysis.

Results:

Seventeen SPSD patients were included; 65% had Classic SPS; 35% had SPS-plus. The mean 9HPT completion times were 35.27 seconds (dominant hand; SD: ±18.32) and  37.53 seconds (non-dominant hand; SD ±18.54). The mean SDMT score was 40.53 (SD: ±9.53). In a model adjusted for symptom duration and SPSD diagnosis, older age was significantly associated with lower SDMT scores (Coefficient = -0.3460; 95% CI: -0.6358, -0.0562). After adjusting for age and symptom duration, individuals with SPS-plus took, on average, 22.81 seconds longer (dominant hand; 95% CI: 4.67, 40.95) and 24.97 seconds longer (non-dominant hand; 95% CI: 6.54, 43.40) to complete the 9HPT compared to those with Classic SPS.

Conclusions:

This study highlights the potential use of 9HPT and SDMT in assessing some non-classical features of SPSD. Further studies are needed to assess whether such clinical tools can help monitor function over time.