Neurological Manifestations of Glutamic Acid Decarboxylase Autoimmunity in Indian Patients

Meena Thevarkalam; Sudheeran Kannoth; Vivek Nambiar; Siby Gopinath; Annamma Mathai; Anandkumar Anandakuttan; Sajitha Krishnan; Renjitha Bhaskaran

doi:10.4103/aian.aian_392_23

Neurological Manifestations of Glutamic Acid Decarboxylase Autoimmunity in Indian Patients

Ann Indian Acad Neurol. 2023 Sep-Oct;26(5):663-671. doi: 10.4103/aian.aian_392_23. Epub 2023 Oct 26.

Authors

Meena Thevarkalam¹, Sudheeran Kannoth^{2

3}, Vivek Nambiar², Siby Gopinath², Annamma Mathai^{2

3}, Anandkumar Anandakuttan², Sajitha Krishnan¹, Renjitha Bhaskaran⁴

Affiliations

¹ Department of Biochemistry, Amrita Institute of Medical Sciences, Amrita Viswavidyapeetham University, Kochi, Kerala, India.
² Department of Neurology, Amrita Institute of Medical Sciences, Amrita Viswavidyapeetham University, Kochi, Kerala, India.
³ Department of Neuroimmunology Laboratory, Amrita Institute of Medical Sciences, Amrita Viswavidyapeetham University, Kochi, Kerala, India.
⁴ Department of Biostatistics, Amrita Institute of Medical Sciences, Amrita Viswavidyapeetham University, Kochi, Kerala, India.

Abstract

Objective: To study the neurological manifestations of glutamic acid decarboxylase (GAD 65) autoimmunity in Indian patients.

Methods: Retrospective study conducted in a tertiary care referral hospital in South India. Patients who tested positive for GAD 65 antibodies from February 2013 to July 2019 were included.

Results: We identified 922 patients who underwent GAD 65 testing, of which 81 tested positive (8.78%) [mean age 55.42 years (SD 17.39, range 9-86 years, median age 57 years)]. Males (n = 47) outnumbered the females (n = 34). All the GAD values measured were <5000 IU/ml. There were 34 cases (42%) of atypical parkinsonism (16/34, 47% fulfilled the diagnostic criteria for autoimmune atypical parkinsonism) in our series forming the most common group with GAD 65 positivity, followed by autoimmune encephalitis (8 cases, 9.88%). Men were more affected with atypical parkinsonism (22/34; 64.70%), stiff person syndrome (2/3; 66.66%), and neuropathy (4/7; 57.1%) while women were more with autoimmune encephalitis (6/8; 75%). Eighteen (22.6%) had underlying autoimmunity (three had type 1 diabetes mellitus). Six (7.4%) had underlying neoplasm. Thirty-three out of 43 patients responded to immunotherapy (76.74%). Five had spontaneous improvement.

Conclusion: Glutamic acid decarboxylase65 antibody values were much lower in our study population. Male-dominant autoimmunity was seen unlike that in Western literature. The most striking was the high preponderance of atypical parkinsonism in GAD 65-positive patients. We also found that GAD 65 positivity is a useful marker for a positive response to immunotherapy in suspected autoimmune neurological syndromes irrespective of their titers.

Keywords: Atypical parkinsonism; autoimmune atypical parkinsonism; autoimmune encephalitis; glutamic acid decarboxylase65 antibody.