DISCLAIMER: This link was displayed at 21:50:10 24/04/2024 and expires on 29/04/2024 if printed.

Go to http://testguide.adhb.govt.nz/EGuide/ for more information.

Specimen Collection

Please note: Ideally, paired serum and CSF should be sent for testing, however, we will accept either serum or CSF specimens sent independently. CSF specimens in early stages of the disease will increase assay sensitivity. 

1 mL Sterile Container CSF (Preferred)
4 mL Plain Serum
3.5 mL SST Serum
Turnaround Time: Within 2 days

Tested daily Monday to Friday.

Specimen must be in the department available for analysis by 1030 hours, otherwise testing will be deferred to the next working day

Assay Method

Limbic encephalitis panel           IFA (Transfected cells)         Euroimmun (Germany)

Diagnostic Use and Interpretation

Limbic encephalitis (LE) refers to an inflammatory process localised to structures of the limbic system that produces cognitive impairment along with disordered perception, mood changes and sleep disturbances. It is important to note that the clinical and radiological findings are not restricted to those areas. Both paraneoplastic and non-paraneoplastic encephalitis share many clinical features but also have distinctive features. Response to treatment can be dramatic but it is highly variable.

LE is characterised by acute or sub-acute mood and behavioural changes, short-term memory problems, complex-partial seizures and cognitive dysfunction (1). Hypothalamic dysfunction may also occur, presenting as hyperthermia, somnolence and endocrine abnormalities. Approximately two-thirds of LE patients develop multifocal involvement of the nervous system such as encephalomyelitis. Usually symptom presentation is in the order of days to weeks but there have been cases described where symptoms have evolved over months (1).

The clinical presentation and treatment of NMDAR encephalitis is outlined under NMDAR TG entry and therefore will not be covered here. The additional antigens expressed on the LE biochip are (a) leucine-rich glioma inactivated protein 1 [LGI1] (b) alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor [AMPA 1 and AMPA 2] (c) B1 subunit of the gamma-aminobutyric acid receptor [GABA _B ] and (d) contractin associated protein 2 [CASPR 2].

  LGI 1

Before the identification of LGI 1 secreted protein as a specific target antigen, patients with this type of LE were attributed to antibodies directed against the voltage gated potassium channel (VGKC) complex (2). The LGI 1 protein functions as a ligand for the two epilepsy related proteins of ADAM22 and ADAM 23 (3).

Refer to 'CASPR 2' in this section of the report for the relationship between quantitation of the VGKC complex and the seroprevalence of LGI 1 antibody.

Patients develop memory disturbances, confusion and seizures. Memory and cognitive deficits may be preceded by short faciobrachial dystonic seizures that can be mistaken for myoclonus or dystonia and often do not respond to anti-epileptic drug therapy (4). Some patients may develop hyponatremia or REM sleep behaviour disorders (5).

MRI findings are typical of LE while CSF often has normal total protein levels or may have only oligoclonal banding as the only abnormality (6).

Approximately 15% of cases are paraneoplastic, the commonest neoplasms being thymoma or SCLC (5).

Treatment with a combination of IV methyl prednisone, oral prednisone, IVIG, Mycophenolate and plasma exchange gives significant clinical improvement in up to 80% of patients (7).

  AMPA

Patients with this type of LE have antibodies directed against the glutamate receptors (1 and 2) [Glu1 and Glu2] subunits of the AMPA. The AMPAR's are ionotropic glutamate receptors that mediate most of the fast excitatory neurotransmission in the brain. The regions of the brain with the greatest levels of the Glu1 and Glu2 subunits are the synaptic CA3-CA1 areas of the hippocampus, followed by the subiculum, cerebellum, caudate-putamen and cerebral cortex (8).

Most patients (highest frequency is found in middle aged females) present with the sub-acute onset of confusion, disorientation and memory loss with or without seizures. As the syndrome progresses, clinical features are those of acute limbic dysfunction that can be associated with prominent psychiatric symptoms including aggression / combativeness, hallucinations and confabulation (8).

CSF findings are similar to those of patients with NMDA encephalitis with predominant lymphocytic pleocytosis. Initial brain MRI (FLAIR) shows abnormalities in the medial temporal lobes (5).   Treatment options are as for the other LE's, however for AMPA LE, relapse is common with or without tumour resection. Up to 50% of patients can have a history or concurrent findings of systemic autoimmunity (8). Up to 70% of patients have an underlying neoplasm with the commonest being those of the breast, thymus and SCLC (8).

  GABA _B

GABA is the major inhibitory neurotransmitter in the CNS and, as such, plays a key role in modulating neuronal activity. GABA mediates its action through the iontropic GABA _A and the metabotropic GABA _B receptors. Unlike GABA _A receptors that form ion channels, GABA _B   receptors address secondary messenger systems through the binding and activation of guanine nucleotide binding proteins (G proteins) (9). GABA _B   receptors are widely distributed in the brain and spinal cord, but the highest levels are found in the hippocampus, thalamus and cerebellum (10).

GABA _B LE is a relatively rare disease accounting for approximately 5% of cases (11). The condition is immunoresponsive (80% improvement with immunotherapy and / or tumour excision) and symptoms are similar to those seen in other limbic encephalopathies (12). Between 35-50% of cases, the immune response is paraneoplastic due the presence of SLCC (12).

  CASPR 2

CASPR 2 is a member of the neurexin superfamily that facilitate cell-cell interactions in the nervous system. Specifically, CASPR 2 is a single pass transmembrane protein distinguished from most other neurexins by an extracellular discoidin/neuropilin homology domain and a fibrinogen-like region which mediate cell-cell adhesions and extracellular matrix interactions. The large extracellular region of CASPR 2 also features four lamin G domains and two epidermal growth factor [EGF] domains, predicted to be involved in receptor - ligand interactions, cell adhesion, migration and differentiation (13).

In myelinated axons, potassium channels are concealed under myelin sheaths in the juxtaparanodal region and CASPR 2, in association with TAG-1 (Ig-like cell adhesion molecule) binds CASPR 2 to form a scaffold that is necessary to maintain potassium channels at the juxtaparanodal region. It is proposed that the two proteins in concert allow myelinating glial cells to organise ion channels in the underlying axonal membrane (14).

Patients develop symptoms of encephalitis (cognitive impairment, memory loss hallucinations and seizures) and / or Morvan?s syndrome [MoS] (peripheral nerve hyperexcitability, neuromyotonia, dysautonomia and encephalopathy with marked insomnia) (15, 16).

Antibodies directed against CARPR 2 were the first identified within the VGKC complex in patients with MoS (6). Patients with CASPR 2 antibody associated syndromes respond to immunotherapy (>90%) (17), which is an important point of distinction as the often complex range of symptoms can be confused with an unusual form of motor neuron disease.   Tumours may or may not be present (15).

Findings from a large retrospective study conducted in 2013 at the Mayo Clinic Neuroimmunology Laboratory showed that across all VGKC assay reactivity strengths only 27% of patients (n=316) were seropositive for either LGI 1 and / or CASPR 2 antibodies and, there were diverse clinical manifestations that frequently overlapped. 61% of patients with a high (? 1.0nmol/L) stratified VGKC result [n=17] were seropositive for LGI 1 and / or CASPR 2 antibodies where two-thirds of the group were seropositive for only LGI 1 antibodies. Conversely, of the 288 patients who had VGKC channel concentrations between 0.03-0.99 nmol/L, 62 (21%) were seropositive for LGI 1 and / or CASPR 2 antibodies (18).

 References:

1. Gultekin SH, Rosenfeld MR, Voltz R et al. Paraneoplastic limbic encephalitis: neurological symptoms, immunological findings and tumour association in 50 patients. Brain 2000; 123 [7]:1481-94
2. Lai M, Huijbers MG, Lancaster E et al. Investigation of LGI 1 as the antigen in limbic encephalitis previously attributed to potassium channels: a case series. Lancet Neurol 2010; 9:776-85
3. Fukata Y, Lovero KL, Iwanaga T et al. Disruption of LGI 1-linked synaptic complex causes abnormal synaptic transmission and epilepsy. Proc Natl Acad Sci USA 2010; 107:3799-3804
4. Andrade DM, Tai P, Dalmau J, Wennberg R. Tonic seizures: A diagnostic clue of anti-LGI 1 encephalitis? Neurology 2011; 76:1355-57
5. Rosenfeld MR, Dalmau J. Anti-NMDA-receptor encephalitis and other synaptic autoimmune disorders. Curr Treat Options Neurol 2011; 13(3):324-32
6. Irani SR, Alexander S, Waters P et al. Antibodies to Kv1 potassium channel-complex proteins leucine-rich glioma inactivated 1 protein and contractin-associated protein-2 in limbic encephalitis, Morvan?s syndrome and acquired neuromyotonia. Brain 2010; 133:2734-2748
7. Wong SH, Saunders MD, Larner AJ et al. An effective immunotherapy regimen for VGKC antibody-positive limbic encephalitis. J Neurol Neurosurg Psychiatry 2010; 81:1167-69
8.   Lai M, Hughes EG, Peng X et al. AMPA receptor antibodies in limbic encephalitis alter synaptic receptor location. Ann Neurol 2009; 65:424-434
9. Bettler B, Kaupmann K, Mosbacher J et al. Molecular structure and physiological functions of GABA _B receptor. Physiol Rev 2004; 84:835-67
10. Lancaster E, Lai M, Peng X et al. Antibodies to the GABA _B receptor in limbic encephalitis with seizures: case series and characterisation of the antigen. Lancet Neurol 2010; 9:67-76
11. Lancaster E, Martinez-Hernandez E, Dalmau J. Encephalitis and antibodies to synaptic and neuronal cell surface proteins. Neurology 2011; 77:179-189
12. Kim T-J, Lee S-T, Shin J-W et al. Clinical manifestations and outcomes of the treatment of patients with GABA _B encephalitis. J Neuroimmunology 2014; 270:45-50
13. Rodenes-Cuadrado P, Ho J, Vernes SC. Shining a light on the CNTNAP2: complex functions to complex disorders. European journal of Human Genetics 2014; 22:171-78
14. Poliak S, Salomon D, Elhanany H et al. Juxtaparanodal clustering of shaker-like K ⁺ channels in myelinated axons depends on Caspr2 and TAG-1. The Journal of Cell Biology 2006; 162(6):1149-1160
15. Dalmau J, Rosenfeld MR. Paraneoplastic and autoimmune encephalitis. 2014. http://www.uptodate.com/contents/paraneoplastic-and-autoimmune-encephalitis
16. Irani SR, Pettingill P, Kleopa KA et al. Morvan syndrome: clinical and serological observations in 29 cases. Ann Neurol 2012; 72:241-255
17. Lancaster E, Huijbers MG, Bar V et al. Investigations of Caspr2, an autoantigen of encephalitis and neuromyotonia. Ann Neurol 2011; 69:303-11
18. Klein CJ, Lennon VA, Aston PA et al. Insights from LGI 1 and CASPR 2 potassium channel complex autoantibody subtyping. JAMA Neurol 2013; 70(2):229-234

Contact Information

For further information contact the laboratory, (09) 307 4949 ext 22103 or:
Associate Professor Rohan Ameratunga , Immunopathologist: Locator 93-5724,  

Dr Richard Steele , or  The LabPLUS Immunology Team

Specimen Transport Instructions for Referring Laboratories

Send separated serum under standard cool pack refrigeration conditions

CSF can be transported under ambient temperature conditions

Last updated at 08:08:16 17/06/2022