List the typical findings in the following investigation-disease pairs:

a)    The nerve conduction findings in Guillain-Barre syndrome.    (20% marks)

b)    The cerebral spinal fluid findings in Listeria meningitis.    (20% marks)

c)    MRI features in posterior reversible encephalopathy syndrome (PRES).    (20% marks)

d)    Full blood count and blood film in Vitamin B12 deficiency.    (20% marks)

e)    Plain cervical spine X-ray in ankylosing spondylitis.    (20% marks)
 

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College answer

  1. The nerve conduction findings in Guillain-Barre syndrome
  • May be normal
  • With pure demyelination-Slowed nerve conduction velocities, (temporal dispersion of waveforms, conduction block, prolonged or absent F waves).
  • If axonopathy-reduced amplitude
  1. The cerebral spinal fluid findings in Listeria meningitis
  • Increased WCC with lymphocytosis
  • Elevated protein
  • Reduced glucose
  • Gram positive rods on microscopy
  1. MRI features in posterior reversible encephalopathy syndrome (PRES)
  • T1: hypointense in affected regions
  • T2: hyperintense in affected regions
  • DWI: usually normal
  • ADC: signal increased in affected regions due to increased diffusion
  • SWI: may show microhaemorrhages in up to 50%
  1. Full blood count and blood film in Vitamin B12 deficiency
  • Anaemia
  • Macrocytosis
  • Leucopenia/thrombocytopenia
  • Low reticulocyte count
  • Hypersegmented neutrophils
  1. Plain cervical spine x-ray in ankylosing spondylitis
  • Squaring vertebral bodies
  • Ankylosis facet joints
  • “Bamboo spine”

Examiners Comments:

Generally poor knowledge in this area with many factual errors in some candidates’ answers.

Discussion

Though some might say that a test of analytic capabilities is more important, it is clearly still relevant for the college to make sure their trainees have strong semantic memory, even though more recently data storage has been extensively outsourced to external structures such as the Internet. One may still argue that the 31.8% of trainees who were able to effortlessly recall these details would make slightly sharper intensivists. 

The nerve conduction findings in Guillain-Barre syndrome

Some very old diagnostic guidelines from 1990 (Asbury & Cornblath)

  • Nerve conduction slowing in 80% of cases at some point during the illness (velocity is usually less than 60% of normal), which is consistent with demyelination
  • Specific characteristic findings:
    • Partial conduction block
    • Decreased M-responses
    • Temporal dispersion
    • Prolonged distal latencies
    • Prolonged or absent F waves and H-reflexes
  • 20% of cases have normal conduction studies
  • Sensory conduction studies are occasionally abnormal (reduction in evoked amplitude)
  • Axonal disease features absent or severely reduced compound muscle action potential amplitudes, with preserved conduction velocities

The cerebral spinal fluid findings in Listeria meningitis

The lymphocyte-rich CSF in Listeria meningitis can occasionally confuse a young player, where "the unwary may dismiss lymphocytic meningitis as being of 'viral' origin", according to an old paper by Hearmon & Ghosh (1989). It is otherwise classical bacterial meningitis (low glucose, high CSF protein, and of course characteristic Gram-postive rods of which there are not many). 

MRI features in posterior reversible encephalopathy syndrome (PRES)

As listed by Bartynski (2008):

  • T1: hypointense in affected regions
  • T1 C+ (Gd): patchy variable enhancement. It can be seen in ~35% of patients, whether leptomeningeal or cortical pattern.
  • T2:  hyperintense in affected regions
  • DWI: usually normal
  • ADC: signal increased in affected regions due to increased diffusion
  • GRE: may show hypointense signal in cases of haemorrhage
  • SWI: may show microhemorrhages 

Full blood count and blood film in Vitamin B12 deficiency

This is from Snow (1999) and UpToDate:

  • Macrocytosis - the MCV tends to increase before anaemia develops. Only a truly massive MCV is sensitive for B12 deficiency (over 130 fL).
  • Hypersegmented neutrophils also precede anaemia - this is the presence of at least one neutrophil with at least 6 lobes or more
  • Anaemia is usually hypochromic and macrocytic
  • Leucopenia/thrombocytopenia and low reticulocyte count reflect poor haematopoiesis
  • Evidence of haemolysis may be present (eg. RBC fragments)

Plain cervical spine x-ray in ankylosing spondylitis 

As the practice of ordering plain C-spine radiographs has largely died out over 10 years ago, it is strange to find it in the 2019 paper, but here we are. From Radiopedia and Østergaard (2012):

  • Romanus lesions of the spine (shiny corner sign): small erosions at the corners of vertebral bodies with reactive sclerosis
  • vertebral body squaring
  • Andersson lesion: noninfectious spondylodiscitis:
  • Bamboo spine: diffuse syndesmophytic ankylosis 
  • Dagger spine: interspinous ligament ossification
  • enthesophyte formation from enthesopathy
  • dural ectasia

References

References

Bartynski, W. S. "Posterior reversible encephalopathy syndrome, part 1: fundamental imaging and clinical features." American Journal of Neuroradiology 29.6 (2008): 1036-1042.

Asbury, Arthur K., and David R. Cornblath. "Assessment of current diagnostic criteria for Guillain‐Barré syndrome." Annals of Neurology: Official Journal of the American Neurological Association and the Child Neurology Society 27.S1 (1990): S21-S24.

Hearmon, Christine J., and Salil K. Ghosh. "Listeria monocytogenes meningitis in previously healthy adults." Postgraduate medical journal 65.760 (1989): 74-78.

Snow, Christopher F. "Laboratory diagnosis of vitamin B12 and folate deficiency: a guide for the primary care physician." Archives of internal medicine 159.12 (1999): 1289-1298.

Østergaard, Mikkel. "Imaging of ankylosing spondylitis." Arthritis Research & Therapy. Vol. 14. No. 2. BioMed Central, 2012.