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A case of a 49-year-old woman with IgG4 anti-Neurofascin155 antibody-positive CIDP in both serum and cerebrospinal fluid

and tremor Abstract Background CIDP (chronic inflammatory demyelinating polyneuropathy) is an autoimmune disorder of peripheral nervous system, causing demyelination and even axonal degeneration. Recently, anti- Neurofascin155 (NF155) antibody-positive CIDP began to cut a figure. This is a special type of CIDP that progressively worsen and predominantly involving distal limbs. IgG4 anti- NF155 antibody-positive CIDP combining serum with CSF in clinical is very rare. The article displayed the clinical practice to evoke the diagnosis of IgG4 anti- NF155 antibody-positive CIDP in front of the disabling tremor and ataxia. We described a rare clinical disorder of IgG4 anti- NF155 antibody-positive CIDP with reviewing some of literatures. Case presentation A 49-year-old woman presented with an evaluation of weakness, numbness and a little ache of all her limbs for half a year. She revealed ataxia, intention tremor and wide-based gait. Cerebrospinal fluid (CSF) results showed the noticeably elevated protein level without pleocytosis. The findings of peripheral nerve conductionNCVindicated marked prolongation of distal and F-wave latencies which conformed to demyelinating polyneuropathy. And her spinal MRI illustrated a thickened right nerve root of sacrum 1-2. IgG4 NF155 antibodies of serum together with CSF were positive by indirect immunofluorescence based on NF155 transfection cells. A high-dosage mythylprednisolone pulse followed by oral prednisolone improved her symptoms. Conclusion Disabling tremor, ataxia, younger onset age, high protein levels in CSF, marked prolongation of distal and F-wave latencies, the roots or plexus of neck and lumbosacral nerves thickening on MRI, and poor response to IVIg may consider as biomarkers of IgG4 anti- NF155 antibody-positive CIDP.


Abstract
Background CIDP (chronic inflammatory demyelinating polyneuropathy) is an autoimmune disorder of peripheral nervous system, causing demyelination and even axonal degeneration. Recently, anti-Neurofascin155 (NF155) antibody-positive CIDP began to cut a figure. This is a special type of CIDP that progressively worsen and predominantly involving distal limbs. IgG4 anti-NF155 antibody-positive CIDP combining serum with CSF in clinical is very rare. The article displayed the clinical practice to evoke the diagnosis of IgG4 anti-NF155 antibody-positive CIDP in front of the disabling tremor and ataxia. We Background CIDP was initially recognized as chronic inflammatory polyradiculoneuropathy by Dyck and colleagues in 1975, but cases consistent with probable CIDP were first described as early as 1958. [8][9][10] According to the reported data, the incidence of CIDP ranges from 0.7 to 1.6 cases per 100,000 persons per year, and the overall prevalence was estimated at 4.8 to 8.9 cases per 100,000 persons [11][12]. Furthermore, IgG4 anti-NF155 antibody-positive CIDP, a special type of CIDP comprises only 7 percent of all types [1,4]. IgG4 anti-NF155 antibody-positive CIDP in clinical, especially in both serum and CSF is very rare.In addition, NF155 is located at the paranode and expressed by the terminal loops of myelin.
The primary role of IgG4 anti-NF155 antibodies may be blockade of interactions between NF155 and Caspr/contactin-1, leading to conduction failure. [5] Recent studies have suggested CIDP gradually gave the priority to disabling tremor and ataxia, which were the key clinical features of IgG4 anti-NF155 antibody-positive CIDP compared to CIDP with negative IgG4 anti-NF155 antibody. [3] The mechanism of marked sensory ataxia and tremor in anti-NF155 antibody-positive CIDP patients is still unclear.
we describe a case of a 49-year-old woman with IgG4 anti-NF155 antibody-positive CIDP.
The pathogenesis, clinical manifestation diagnosis, and treatment of IgG4 anti-NF155 antibody-positive CIDP were discussed by reporting this case and reviewing the relative references. she was identified IgG4 anti-NF155 antibody-positive CIDP. Intravenous immunoglobulin (IVIg) was first used for her treatment, which responded poorly. When her IgG4 anti-NF155 antibodies in serum and CSF were positive, she was given a high-dosage mythylprednisolone (prednisolone,po,)pulse treatment.16 days later, her disabling tremor and ataxia symptoms improved significantly.

Discussion
CIDP is a heterogenous disorder with typical and atypical phenotypes that may share heterogenous pathogenesis. [8] Interestingly, anti-NF155 CIDP shows distinct pathological featuresdiffering from other typical CIDP. NF155 is a member of L1 family of adhesion molecules. NF155 locates in the paranodal loops of demyelinating Schwann cells and 5 associates with the axonal cell adhesion molecules CNTN1 and contactin-associated protein-1(caspr1). [2] In addition, NF155 is one of the targets of the immune response of CIDP, playing a major role in maintaining the structure and function of Ranvier. Therefore, losing of NF155 will lead to serious demyelinating neuropathy and Purkinje neuron degeneration. Then disabling characteristic tremor (high amplitude, low frequency, postural and intention) and ataxia come to appearing on patients, [3] exactly as the woman of this case report.
Except for disabling characteristic tremor and ataxia, IgG4 anti-NF155 antibody-positive CIDP also has other typical clinical features. Compared with other types of CIDP, patients with IgG4 anti-NF155 antibodies significantly associate with younger onset age around of 20-30 years instead of 50-60 , [5] Besides, the protein concentration in CSF is higher than normal values. [5] The nerve electrophysiology suggests marked prolongation of distal and F-wave latencies. [5] All of these symptoms were observed in the woman in case report.
Furthermore, one distinguishing feature is that the roots or plexus of neck and lumbosacral nerves thickening on MRI can be found in most cases. [2][3]5] The woman in this case also showed a thickened right nerve root of sacrum 1-2.
The diagnosis of CIDP still relies on a combination of clinical and electrophysiological criteria. [1] Based on these conditions, when IgG4 anti-NF155 antibodies were detected in serum or CSF, would you can diagnose IgG4 anti-NF155 antibody-positive CIDP.
Corticosteroids, intravenous immunoglobin , and/or plasmapheresis can provide short-term benefits. [6] Maintenance therapy with IVIg can induce sustained remission, increase quality of life and prevent further axonal loss. [6] The reason why IVIg can be used to treat CIDP is that it can block the Fc part of antibody and inhibit the complement pathway. [7] However, IgG4 anti-NF155 antibody-positive CIDP poor response to IVIg . [3] IgG4 antibodies do not bind to C1q and have low affinity to Fc receptors and complement. [1,3] 6 Therefore, the treatment of IgG4 anti-NF155 antibody-positive CIDP mainly depends on corticosteroids.

Consent for publication
Written informed consent was obtained from the patient for publication of this Case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

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Availability of data and material All data generated or analyzed during this study are included in this published article and its supplementary information files.

Competing interest
The author declare that they have no competing interests.