Effects of immunotherapy on motor cortex excitability in Stiff Person Syndrome

SPS: Understanding the complexity

INTRODUCTION

Stiff-person syndrome (SPS), first described in 1956 by Moersch and Woltman, is a progressive autoimmune disorder with core features of chronic fluctuating progressive truncal and limb rigidity and painful muscle spasms leading to gait difficulties, falls and an appearance that resembles tin soldiers. The syndrome is a rare, highly disabling disorder of the central nervous and frequently results in significant disability. Understanding of the etiology, clinical spectrum, diagnostic workup and therapeutic modalities for this painful and disabling disorder has vastly evolved over the past few years with more confidence in classifying and treating the patients. The purpose of this review is to increase the awareness, early detection, and treatment of this disabling disease.

METHOD

PubMed was searched, all date inclusive, using the following phrases: stiff person syndrome,anti-Glutamic acid decarboxylase (Anti-GAD) antibody syndrome, Progressive encephalomyelitis with rigidity and myoclonus (PERM), and Paraneoplastic Stiff Person syndrome. No filters or restrictions were used. A total of 888 articles were identified.

RESULTS

The results were narrowed to 190 citations after excluding non-English and duplicate reports. Clinical presentation, laboratory testing, treatment, and prognosis were categorized and summarized.

DISCUSSION

In this article we will discuss the epidemiology, presentation and classification. Explain the pathophysiology of SPS and the autoimmune mechanisms involved. Discuss the diagnostic approach and treatments available, as well as, the prognosis and outcome.

Autoimmune stiff person syndrome and related myelopathies: understanding of electrophysiological and immunological processes

Stiff person syndrome (SPS) is a disabling autoimmune central nervous system disorder characterized by progressive muscle rigidity and gait impairment with superimposed painful spasms that involve axial and limb musculature, triggered by heightened sensitivity to external stimuli. Impaired synaptic GABAergic inhibition resulting from intrathecal B-cell-mediated clonal synthesis of autoantibodies against various presynaptic and synaptic proteins in the inhibitory neurons of the brain and spinal cord is believed to be an underlying pathogenic mechanism. SPS is most often idiopathic, but it can occur as a paraneoplastic condition. Despite evidence that anti-GAD and related autoantibodies impair GABA synthesis, the exact pathogenic mechanism of SPS is not fully elucidated. The strong association with several MHC-II alleles and improvement of symptoms with immune-modulating therapies support an autoimmune etiology of SPS. In this review, we discuss the clinical spectrum, neurophysiological mechanisms, and therapeutic options, including a rationale for agents that modulate B-cell function in SPS.

A critical update on the immunopathogenesis of Stiff Person Syndrome

BACKGROUND

Stiff Person Syndrome (SPS) is a relatively rare but often overlooked autoimmune neurological disorder that targets antigens within the brain's inhibitory pathways resulting in incapacitating stiffness and spasms that impact on the patients' quality of life. Although a number of immunomodulating therapies significantly improve the patients' symptoms, the exact pathogenic mechanisms remain unclear.

MATERIALS AND METHODS

The current literature on SPS was reviewed and combined with the authors' experience with many patients and various laboratory studies. The majority of the patients have high-titre anti-GAD (Glutamic Acid Decarboxylase) antibodies in the sera and CSF suggesting dysfunction of the GABAergic neurotransmission. These antibodies are excellent disease markers but their pathogenic role remains uncertain.

CONCLUSIONS

This review provides a critical assessment on the immunobiology of SPS, describes the identification of anti-GABARAP antibodies as a new antigenic target in the GABAergic synapse and identifies the areas for future research.