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Introduction: It is known that in subjects with antibodies to
glutamic acid decarboxylase (GAD-ab) the spectrum of
neurological symptoms comprises stiff-person-syndrome (SPS),
cerebellar ataxia and limbic encephalitis as well as some less
common conditions. However, dementia has only rarely been
described in association with GAD-ab.
Case report: A 60-year old Swiss female was referred for
diagnostic work-up of gait disturbances and cognitive
impairment. Gait disturbances had evolved within several days,
thereafter the progression had slowed down; however, at the
time of referral she was already severely impaired by her gait
disorder. Furthermore she complained about increasing cognitive
disturbances particularly in visually estimating distances and
about an increased error rate during writing despite proof
reading.
Results: On clinical examination she disclosed marked
cerebellar ataxia, gaze evoked nystagmus, positive frontal
release signs, torticollis, slightly increased muscle tone,
exaggerated tendon reflexes on her lower limbs and a positive
Babinski sign. Neuropsychological examination revealed severe
deficits in attention, visuospatial function and short-term memory.
Moreover, behavior was disinhibited. MR scan of the brain
showed supra- and infratentorial atrophy without any evidence
for focal lesions. Screening for vasculitis, putative infectious
diseases, prion diseases and several degenerative and
metabolic forms of ataxia or dementia remained negative. Due
to the clinical presentation with a subacute cerebellar ataxia,
GAD-ab testing was considered. Testing showed very high
levels of serum GAD-ab, thus leading to the diagnosis of GAD
antibody-associated ataxia and dementia.
Conclusion: Several neurological symptoms including SPS and
cerebellar ataxia were found to be associated with elevated
GAD-ab titers, suggesting an immune-mediated process in these
conditions. The clinical presentation of a subacute cerebellar
ataxia encouraged us to test for GAD-ab in this patient. Rapidly
progressive dementia can be caused by autoimmune diseases,
namely in conjunction with voltage-gated potassium channel
(VGKC) and GAD autoimmunity. Actually, the clinical picture of
the presented patient would have fit well with CJD. As we excluded numerous putative etiologies of dementia or ataxia
including prion diseases, we conclude that raised GAD-ab levels
are likely to be causative for the neurological symptoms including
dementia in this case.