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PubMed This is a summary of 16 peer-reviewed journal articles Updated

The Science of Your Diagnosis: Biological Markers and Testing

At a Glance

To diagnose Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP), doctors use a lumbar puncture to check for high spinal fluid protein and an EMG to detect nerve conduction blocks. These tests confirm the immune system is attacking nerve insulation.

When you are diagnosed with Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP), your medical team uses several specialized tests to look “under the hood” at your nervous system. These tests look for specific biological signatures that distinguish AIDP from other conditions.

The Biology: An Immune-System Misunderstanding

In AIDP, your immune system mistakenly identifies the myelin (the insulation on your nerves) as a threat.

  • Macrophage Attack: Specialized immune cells called macrophages are the primary “soldiers” in this attack [1]. They physically strip away the myelin at specific points along the nerve fibers, particularly near the nodes (the gaps in the insulation where signals jump) and the internodes (the long sections of insulation) [1][2].
  • Conduction Block: When the insulation is gone, the electrical signal cannot “jump” properly from one section of the nerve to the next. This is called a conduction block—the signal from your brain essentially hits a wall and never reaches the muscle [3][4].

The Lumbar Puncture (Spinal Tap)

A lumbar puncture is used to analyze the cerebrospinal fluid (CSF) that surrounds your brain and spinal cord.

  • Albuminocytologic Dissociation: This is the classic finding for AIDP. It means that the protein levels in your spinal fluid are high, but the white blood cell count remains normal or low [5][6]. This “dissociation” (a gap between the two numbers) is a strong indicator that the immune system is active around the nerves without a full-blown infection in the fluid [5].
  • Timing Matters: In about 43% of cases, protein levels are normal if the test is done within the first few days [5]. By the end of the first week, over 80% of patients will show this elevated protein signature [5][7].

The EMG/NCS: Auditing Your Reports

An Electromyogram (EMG) and Nerve Conduction Study (NCS) measure how well your nerves are sending signals. Here are terms you might see on your report:

  • A Waves: These are extra electrical signals that appear when a nerve is irritated or demyelinated. They are often one of the earliest signs of AIDP [8][9].
  • Sural-Sparing Pattern: This is a very specific clue for AIDP. It means that while the nerves in your arms (like the median or ulnar nerves) are struggling, the sural nerve in your leg is still sending signals normally [10][11]. This unusual mix of “sick” and “healthy” nerves is highly characteristic of AIDP [10].
  • Prolonged Distal Latency: This means the signal takes too long to travel to the very end of the nerve, indicating that the insulation is thin [4][12].

Brighton Criteria: Level of Certainty

Doctors use the Brighton Criteria to determine how certain they are of a GBS/AIDP diagnosis [13]. It combines your clinical symptoms (like symmetric weakness) with your test results (like CSF protein and EMG findings).

  • Level 1 is the highest level of diagnostic certainty, meaning the patient meets all clinical and laboratory criteria [14].
  • Levels 2 and 3 mean the diagnosis is still very likely, but some test results may be pending or less definitive [13].

Emerging Biomarkers

You may hear about new markers like Neurofilament Light (NfL), NfH, or GFAP [15]. These are structural proteins that leak out of a nerve when it is damaged [16]. Please note: These biomarkers are currently used mostly in research settings [15]. Do not panic if your doctor has not ordered these tests; standard clinical care relies on your symptoms, spinal tap, and EMG/NCS, and you are not receiving substandard care if these specific markers are omitted.

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Common questions in this guide

What does 'albuminocytologic dissociation' mean on my spinal tap?
This means your cerebrospinal fluid has high protein levels but a normal or low white blood cell count. This is a classic sign of AIDP, showing that the immune system is active around the nerves without a full-blown infection in the fluid.
Why did my early lumbar puncture show normal protein levels?
Protein levels in the spinal fluid often take time to rise. If a spinal tap is done within the first few days of symptoms, protein may still be normal, but it typically increases by the end of the first week of illness.
What is a 'sural-sparing pattern' on my EMG report?
A sural-sparing pattern means the nerves in your arms show damage, but the sural nerve in your leg remains healthy and sends signals normally. This unusual mix of affected and unaffected nerves is a very specific indicator of AIDP.
What is a conduction block and why does it cause weakness?
A conduction block occurs when the protective myelin insulation on your nerves is stripped away. This prevents electrical signals from traveling properly from your brain to your muscles, which is why your muscles feel so weak.
What are the Brighton Criteria?
The Brighton Criteria help doctors determine how certain they are of an AIDP or GBS diagnosis. The criteria combine your clinical symptoms, like symmetric weakness, with diagnostic laboratory results like spinal taps and EMGs.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.My lumbar puncture shows high protein but low white blood cells; does this 'albuminocytologic dissociation' help confirm the AIDP diagnosis?
  2. 2.On my EMG report, does it mention 'A waves' or a 'sural-sparing pattern'? What do those tell you about my specific subtype?
  3. 3.What 'Brighton Level' of diagnostic certainty do I meet based on my clinical symptoms and test results?
  4. 4.Do my tests show any 'conduction block,' and does that explain why my muscles feel so weak?
  5. 5.If we tested for biomarkers like NfL or GFAP, would that change my treatment plan or predicted recovery timeline?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (16)
  1. 1

    Ultrastructural mechanisms of macrophage-induced demyelination in Guillain-Barré syndrome.

    Koike H, Fukami Y, Nishi R, et al.

    Journal of neurology, neurosurgery, and psychiatry 2020; (91(6)):650-659 doi:10.1136/jnnp-2019-322479.

    PMID: 32245766
  2. 2

    Ultrastructural mechanisms of macrophage-induced demyelination in CIDP.

    Koike H, Nishi R, Ikeda S, et al.

    Neurology 2018; (91(23)):1051-1060 doi:10.1212/WNL.0000000000006625.

    PMID: 30429275
  3. 3

    Effect of intravenous immunoglobulin and plasmapheresis on nerve conduction parameters compared to the natural course of Guillain-Barré syndrome.

    Kalita J, Mahajan R, Kumar M

    Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia 2024; (125()):76-82 doi:10.1016/j.jocn.2024.05.016.

    PMID: 38759351
  4. 4

    Clinical Significance of A Waves in Acute Inflammatory Demyelinating Polyradiculoneuropathy.

    Lakshminarasimhan S, Venkatraman C, Vellaichamy K, Ranganathan L

    Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society 2018; (35(5)):415-418 doi:10.1097/WNP.0000000000000480.

    PMID: 29847438
  5. 5

    CSF Findings in Relation to Clinical Characteristics, Subtype, and Disease Course in Patients With Guillain-Barré Syndrome.

    Al-Hakem H, Doets AY, Stino AM, et al.

    Neurology 2023; (100(23)):e2386-e2397 doi:10.1212/WNL.0000000000207282.

    PMID: 37076309
  6. 6

    Albuminocytologic Dissociation and the Impact of Age-Adjusted Cerebrospinal Fluid Protein Levels in Guillain-Barré Syndrome.

    Thatikonda N, Lerint A, Takle C, et al.

    Neurology international 2025; (17(2)) doi:10.3390/neurolint17020018.

    PMID: 39997649
  7. 7

    Prognostic Implications of Early Albuminocytological Dissociation in Guillain-Barré Syndrome.

    Vargas-Cañas ES, Galnares-Olalde JA, León-Velasco F, et al.

    The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 2023; (50(5)):745-750 doi:10.1017/cjn.2022.288.

    PMID: 35979659
  8. 8

    Guillain-Barré Syndrome with Discharges Following Compound Muscle Action Potentials: A-waves, M Dispersion or After-Discharges?

    Baslo SA, Karaağaç N, Öge AE

    Noro psikiyatri arsivi 2025; (62(4)):393-397 doi:10.29399/npa.28925.

    PMID: 41383896
  9. 9

    Differentiation Between Guillain-Barré Syndrome and Acute-Onset Chronic Inflammatory Demyelinating Polyradiculoneuritis-a Prospective Follow-up Study Using Ultrasound and Neurophysiological Measurements.

    Grimm A, Oertl H, Auffenberg E, et al.

    Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 2019; (16(3)):838-847 doi:10.1007/s13311-019-00716-5.

    PMID: 30756363
  10. 10

    Role of "Sural Sparing" Pattern (Absent/Abnormal Median and Ulnar with Present Sural SNAP) Compared to Absent/Abnormal Median or Ulnar with Normal Sural SNAP in Acute Inflammatory Demyelinating Polyneuropathy.

    Surpur SS, Govindarajan R

    Frontiers in neurology 2017; (8()):512 doi:10.3389/fneur.2017.00512.

    PMID: 29085327
  11. 11

    A Study of Sensory Nerve Conduction in Pre- and Post-immunoglobulin Treatment of Guillain-Barré Syndrome.

    A P, Shende V, Pawar S

    Cureus 2024; (16(1)):e51673 doi:10.7759/cureus.51673.

    PMID: 38313916
  12. 12

    Study of total duration of distal compound muscle action potential in demyelinating and axonal Guillain-Barre' syndrome.

    Ginanneschi F, Cioncoloni D, Capoccitti G, et al.

    Neurological research 2023; (45(4)):381-389 doi:10.1080/01616412.2022.2148517.

    PMID: 36403142
  13. 13

    Clinical Features and the Validation of the Brighton Criteria in Guillain-Barré Syndrome: Retrospective Analysis of 72 Hospitalized Patients in Three Years.

    Zeng Y, Liu Y, Xie Y, et al.

    European neurology 2019; (81(5-6)):231-238 doi:10.1159/000503101.

    PMID: 31574518
  14. 14

    Guillain-Barré syndrome in Bangladesh: validation of Brighton criteria.

    Islam MB, Islam Z, Farzana KS, et al.

    Journal of the peripheral nervous system : JPNS 2016; (21(4)):345-351 doi:10.1111/jns.12189.

    PMID: 27616152
  15. 15

    Neuronal inflammation-associated biomarkers in cerebrospinal fluid of patients with acute and chronic inflammatory demyelinating polyneuropathies.

    Atasever Ü, Akünal C, Soytürk H

    Journal of neuroimmunology 2025; (409()):578756 doi:10.1016/j.jneuroim.2025.578756.

    PMID: 40953545
  16. 16

    Neurofilament Light Chain Levels as Diagnostic and Prognostic Biomarkers in Guillain-Barré Syndrome: An Updated Systematic Review and Meta-Analysis.

    Siconolfi G, Vitali F, Sciarrone MA, et al.

    Neurology and therapy 2025; (14(6)):2387-2410 doi:10.1007/s40120-025-00830-x.

    PMID: 40976818

This page explains AIDP diagnostic testing and biomarkers for educational purposes only. Always consult your medical team to interpret your specific lumbar puncture, EMG results, and diagnostic criteria.

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