Objective:

We aim to explore if comorbid IDDM in patients with SPS affects symptom severity at disease onset or progression, responsiveness to IVIG, and long-term disability compared to patients without IDDM.

Background:

SPS is an autoimmune disease due to impaired GABAergic inhibitory neurotransmission that presents with muscle stiffness, painful muscle spasms, hyperexcitability, and gait dysfunction.  While the association between SPS and IDDM is well-established and both involve glutamic acid decarboxylase (GAD) antibodies directed against different epitopes, the impact of IDDM on SPS symptomatology, disease progression, and responsiveness to IVIG remains unexplored.

Design/Methods:

We conducted a retrospective chart review on 62 patients with GAD65-positive SPS who were diagnosed and managed by the same neurologists with expertise in SPS. Age of symptom onset, time to diagnosis, modified Rankin Scale (mRS) at diagnosis, initial responsiveness to IVIG, and incidence of cerebellar variant phenotype were compared between SPS patients with or without IDDM.

Results:

Of the 62 patients, 21 (34%) had IDDM; in 15 (71%) of them, IDDM preceded SPS diagnosis. Patients with IDDM reported earlier symptom onset (41, range 18-72) compared to patients without IDDM (48, range 24-78), although time to diagnosis did not differ. Average mRS at presentation was similar (2 with IDDM vs. 2.5 without IDDM). No significant difference was noted in initial response to IVIG between patients with IDDM (78%) and those without IDDM (71%). There was no difference in incidence of cerebellar variant.

Conclusions:

While patients with IDDM presented earlier with SPS, time to diagnosis after symptom onset and disease severity at diagnosis were similar, indicating that IDDM does not accelerate SPS progression or significantly affect disability. Initial responsiveness to IVIG was also similar. Long-term responsiveness to IVIG between the two SPS groups and whether IDDM induces neuropathic symptoms that affect disability, IVIG tolerance, and overall quality of life are being assessed.