Inositol 1,4,5-trisphosphate receptor type 1 autoantibody (ITPR1-IgG/anti-Sj)-associated autoimmune cerebellar ataxia, encephalitis and peripheral neuropathy: review of the literature

Background

In 2014, we first described novel autoantibodies to the inositol 1,4,5-trisphosphate receptor type 1 (ITPR1-IgG/anti-Sj) in patients with autoimmune cerebellar ataxia (ACA) in this journal. Here, we provide a review of the available literature on ITPR1-IgG/anti-Sj, covering clinical and paraclinical presentation, tumour association, serological findings, and immunopathogenesis.

Methods

Review of the peer-reviewed and PubMed-listed English language literature on ITPR1-IgG/anti-Sj. In addition, we provide an illustrative report on a new patient with ITPR1-IgG-associated encephalitis with cognitive decline and psychosis.

Results

So far, at least 31 patients with serum ITPR1-IgG/anti-Sj have been identified (clinical information available for 21). The most common manifestations were ACA, encephalopathy with seizures, myelopathy, and (radiculo)neuropathy, including autonomic neuropathy. In 45% of cases, an underlying tumour was present, making the condition a facultative paraneoplastic neurological disorder. The neurological syndrome preceded tumour diagnosis in all but one case. In most cases, immunotherapy had only moderate or no effect. The association of ITPR1-IgG/anti-Sj with manifestations other than ACA is corroborated by the case of a 48-year-old woman with high-titre ITPR1-IgG/anti-Sj antibodies and rapid cognitive decline, affecting memory, attention and executive function, and psychotic manifestations, including hallucinations, investigated here in detail. FDG-PET revealed right-temporal glucose hypermetabolism compatible with limbic encephalitis. Interestingly, ITPR1-IgG/anti-Sj mainly belonged to the IgG2 subclass in both serum and cerebrospinal fluid (CSF) in this and further patients, while it was predominantly IgG1 in other patients, including those with more severe outcome, and remained detectable over the entire course of disease. Immunotherapy with intravenous methylprednisolone, plasma exchange, and intravenous immunoglobulins, was repeatedly followed by partial or complete recovery. Long-term treatment with cyclophosphamide was paralleled by relative stabilization, although the patient noted clinical worsening at the end of each treatment cycle.

Conclusions

The spectrum of neurological manifestations associated with ITPR1 autoimmunity is broader than initially thought. Immunotherapy may be effective in some cases. Studies evaluating the frequency of ITPR1-IgG/anti-Sj in patients with cognitive decline and/or psychosis of unknown aetiology are warranted. Tumour screening is essential in patients presenting with ITPR1-IgG/anti-Sj.

Purkinje cell (PC) antibody positivity in a patient with autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy

PURPOSE

This case report is the first to describe the detection of antibodies against inositol 1,4,5-trisphosphate receptor 1 (ITPR1, I3PR) in a patient diagnosed with autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy. ITPR1 is known as one of the Purkinje cell antibodies present in autoimmune cerebellar ataxia (ACA). Here, we described the association between autoimmune GFAP astrocytopathy and autoimmune cerebellar disease (ACD).

MATERIALS AND METHODS

Demographic features, clinical characteristics, cerebrospinal fluid (CSF) parameters and neuroimaging findings were collected from this patient. Specifically, antibodies against GFAP and other proteins associated with neurological disorders were measured by immunofluorescence staining in both serum and CSF samples.

RESULTS

A 52-year-old woman was diagnosed with autoimmune inflammatory meningoencephalitis. She presented with cognitive dysfunction, psychiatric/behavioral abnormalities and serious insomnia with subacute onset. Brain magnetic resonance imaging (MRI) showed bilateral hyperintensity in the semioval centers on axial images and perivascular linear enhancement oriented radially to the ventricles on sagittal images. GFAP-IgG, oligoclonal bands (OBs), N-methyl-D-aspartate receptor (NMDAR)-IgG and ITPR1-IgG co-existed in her CSF. She responded well to immunoglobulin and steroid treatments.

CONCLUSION

Here, we describe the case of a patient with autoimmune GFAP astrocytopathy whose CSF was positive for ITPR1-IgG; however, she did not show typical ataxia manifestations or cerebellar lesions on her MRI scan. This suggests that ITPR1-IgG is not pathogenic, and the positivity of this antibody in CSF is probably associated with the presence of autoimmune inflammation.