Sunday 12 February 2012

Guillain Barre syndrome MRI

A 40 yo male with sudden progressive weakness and numbness started in bilateral lower limb then both the upper limbs. On neurological examination absent lower limb reflexes.
Clinical diagnosis : Guillain Barre syndrome.
On admission MRI Sagittal T2 screening of whole spine for cord was normal.
MRI study of lumbar region repeated with intra venous contrast showed abnormal enhancement along nerve roots of cauda equina on post contrast T1w images consistent with clinical diagnosis of GB syndrome.

NB : Diagnosis of GBS is solely based on clinical grounds. The eponym "GBS" be reserved for cases where an underlying aetiology is not found, the remainder being called acute inflammatory polyradiculoneuropathy.
In polyneuropathy apart from Cauda equina, Brachial plexus and Peripheral nerves can also be involved. Both humoral and cell-mediated immune mechanisms have been proposed.

Anatomy of Cadua equina and Pathophysiology of enhancement: 
Spinal cord lower end called conus ends at ~D12 – L1 disc level. Lumbar and sacral nerve root which leave cord collectively has to travel intra durally in spinal canal for a long distance before they exit out of their respective neural foramen. This bunch of nerve roots within the lumbar sub arachnoid space called cauda equina.
Along the nerve roots, the endoneurial and penineunai capillaries constitute a true blood-nerve barrier for free exchange of water-soluble non electrolytes, proteins, ions and is very equivocal to the intra cranial blood – Brain barrier. Along these intra dural nerve roots this barrier is less selective and easily susceptible to any nonspecific insult like trauma, ischemia, inflammation, demyelination or axonal degeneration. The disruption of this blood – nerve barrier allow an intravascular contrast agent to escape the vasa nervorum and enter the endoneunium resulting in enhancement of nerve roots of cauda equina on MR T1w images.

Three main patterns of enhancement have been described:
1 ) Linear, smooth, delicate enhancement on the surface of the spinal cord and/or nerve roots.
2)  Nodular pattern consisting of enhancing discrete foci on the surface of the spinal cord and/or nerve roots.
3) Diffuse, thick intra dural enhancement of the lepto meninges, completely surrounding the spinal cord and partially or completely obliterating the thecal sac.

MRI imaging technique for cauda equina: 
In MRI imaging of spine, the standard protocol is Sagittal T1 and T2 w sections parallel spinal axis.  Axial T1 and T2 sections the level of discs parallel to disc. At the most we run Sagittal STIR for bone marrow evaluation. This is protocol is adequate and very well suitable for any level degenerative disc diseases with cord or nerve root compression. But for better evaluation of cauda equina certain changes need to be done as routine Sagittal T1 and T2 screening of lumbar region spine may be normal and miss the pathology. On T1w images nerve roots are slightly hyperintense to Csf. Better appreciated on T2w images as iso intense linear threads without any clumping or nodularity against background of hyperintense Csf. Post contrast T1 is needed to look for any abnormal enhancement along nerve roots of cauda equina. Addition of Fat sat T1 can further increase the sensitivity of study.

DDs of abnormal enhancement of nerve roots of Cauda equina: 
Normally nerve roots of cauda equina don’t enhance. Any enhancement considered as abnormal. Enhancement of cauda equina nerve roots is a nonspecific finding, suggests breakdown of the blood-nerve barrier due to any reason.
DDs include:
Acute inflammatory polyneuropathy.
Chronic inflammatory demyelinating polyneuropathy.
AIDS-related cytomegalovirus polyradiculopathy.
Granulomatous -  Tuberculosis , Sarcoidosis.
Infiltrating neoplastic disorders like lymphoma, metastasis.
Transverse myelitis.
Nerve root compression by herniated disc.
Idiopathic - GBS.

Guillain Barre syndrome (GBS)

An Acute Inflammatory Demyelinating Polyneuropathy (AIDP).
Has autoimmune background, predominantly affecting peripheral nervous system usually preceded by an antecedent bacterial or viral infection.
Presents as an ascending paralysis, weakness in lower limbs to begin with followed by involvement of upper limbs and the face. Loss of deep tendon reflexes is typical on neurological examination. Associated with hypo reflexia or areflexia, autonomic dysfunction and cranial nerve involvement.
Miller Fisher syndrome (MFS) is a rare variant of GBS and manifests as a descending paralysis, proceeding in the reverse order of the more common pattern of GBS.
~ 40% of patients are seropositive for Campylobacter jejuni.
Diagnosis is solely based on clinical grounds, lumbar puncture and electrophysiologic crtieria.
CSF examination may show elevated protein level without pleocytosis.
Nerve Conduction Velocity (NCV) study may show abnormal slowing, conduction block, prolonged distal latency, prolonged or absent F waves.
Role of MRI is to exclude other causes. On MRI findings usually include thickening and enhancement of the nerve roots of the cauda equina. The lymphocytic and macrophagic infiltration around endoneural vessels with associated demyelination of the affected nerves is suggested mechanism behind this abnormal enhancement.
Treatment options include supportive, immunoglobulin and plasmapharesis.


Hernalsteen D, Cosnard G, Peeters A, et al. Lumbar Plexus Involvement with Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): A Variant Case of the Generic Disorder. JBR-BTR 2005;88:322-4.
Li H-f, Ji X-j. The Diagnostic, Prognostic, and Differential Value of Enhanced MR Imaging in Guillain-Barré Syndrome. AJNR Am J Neuroradiol 2011;32:E140. doi:10.3174/ajnr.A2620

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