A case of abnormal CSF chemistry results

HOSP # WARD Neurology Ward
CONSULTANT   Jody Rusch DOB/AGE 17 y Female

Abnormal Result

Increased CSF IgG / albumin Index

Decreased CSF Glucose

Presenting Complaint

At this admission, she presented to Groote Schuur Hospital with a history of parasthesias and lower limb weakness. Her symptoms have had a rapid progression to completed paraplegia, with loss of sphincter control over three days. She does not report altered sensorium or alteration in her sleep wake cycle.

History

The patient had two prior episodes of TB and Systemic Lupus Erythematosis, which was diagnosed in 2017. Her presenting symptoms was malar rash, arthralgia, and having positive serological markers.

She has subsequently been diagnosed with class-II nephritis and autoimmune haemolytic anaemia. She was on maintenance immunosuppression regimen of prednisone and azathioprine between 2017-19.

She has had two prior episodes of TB in 2014 and 2018.

She was diagnosed with optic neuritis in October 2019, after she developed visual loss in her left eye with no perception of light. Retrospectively she reports a prior episode of unilateral visual loss in her right eye in February 2019, consistent with an episode of ON. On the basis of her ON she had her immunosuppression escalated to monthly pulses of cyclophosphamide, from November 2019 until march 2020.

She has now developed an acute severe inflammatory longitudinally extensive myelitis, as result of seropositive Neuromyelitis Optica Spectrum Disorder (NMOSD).

Neuromyelitis Optica Spectrum Disorder, or NMOSD, is a rare, lifelong and debilitating autoimmune disease of the central nervous system (CNS), characterized by inflammation in the optic nerve and spinal cord.

Examination

Higher function examination was normal. Cranial nerve examination revealed bilaterally dilated pupils with sluggish responses. Relative afferent pupillary defect (RAPD) was noted in the left eye. Visual acquity is reduced in both eyes, with the left being more severely affected than the right. Fundoscopy showed bilateral disc pallor, no active papillitis. She had no further cranial nerve or bulbar signs. Upper limb motor examination showed paratonia in the right upper limb. The left had mild loss of dexterity and power in her left hand. Reflexes were symmetrical. Power in her lower limbs was reduced with 0/5 power, she would have intermittent involuntary movements to tactile stimuli. She was hypertonic with a triple response. She has a T4 sensory level to light touch and pin prick and has marked joint position sensation loss in both her legs.

The patient was admitted for evaluation of her Myelitis. She was started on high dose methylprednisolone and after 3 days of no response she was started on Plasma exchange. Her spastic paraplegia remains unchanged. She has received pressure care, physiotherapy, OT and bowel regimen in the ward. Given her young age, and aggressive disease (developing an severe acute inflammatory myelopathy while on monthly cyclophosphamide pulse therapy), Department of Internal Medicine hopes she can undergo induction therapy with rituximab (375mg/m2) for her seropositive NMOSD in the hopes of avoiding progressive disability and recovering some voluntary function of her limbs.

Laboratory Investigations

CSF Glucose

CSF glucose was 1.4 mmol/L. This is low. It is unfortunately not known what the plasma glucose was at that time, as it wasn’t sent with a plasma glucose sample at the same time, as one would have hoped. If one assumes the plasma glucose have been normal (3.5-5.5mmol/L) and that CSF glucose’s normal range is 0.6-0.8 x plasma glucose, then this value (0.4 – 0.25 that of serum) is significantly low.

Low CSF glucose is indicative of:

  • bacterial meningitis,
  • mycobacterial infection (TB meningitis),
  • mycoplasmal infection and
  • fungal infection in the CSF.
  • Leucocytes may also decrease CSF glucose – thus it may indicate a disease process rather than only bacterial infection.

CSF Protein

CSF protein of 2.47 g/L (0.15 – 0.45 g/L) is significantly raised. This is indicative of increased permeability of the blood-CSF barrier, most commonly due to inflammatory conditions, but can also be elevated due to:

  • Decreased spinal CSF flow above the sampling level due to:
    • abscess
    • tumor (see also Froin Syndrome)
    • collapsed intervertebral disc
      • These allow for increased equilibration of fluid between CSF and plasma.
  • Immune response within the CSF (intrathecal synthesis of IgG)
  • Destruction of brain tissue releasing proteins directly into CSF.
  • Neonates (term and pre-term) have a higher reference range – up to 1.7 g/L.

CSF Albumin

CSF albumin of 1271 mg/L (100 – 300) is elevated. This value is increased significantly, likely indicating an increase in the permeability of the blood-brain-barrier (severe impairment).

CSF Albumin Index

The CSF Albumin Index was 31.8 mg/g (<9).

CSF albumin is best interpreted in conjunction with the serum albumin. CSF albumin is corrected for leaking of albumin from the serum (thus incorporating the serum albumin concentration). This is called the CSF albumin index (mg/g) = CSF albumin(mg/L) / serum albumin (g/L)

  • <9: intact blood-CSF barrier
  • 9-14: slight impairment
  • 14-30: moderate impairment
  • >30: severe impairment

CSF IgG / Albumin Index

CSF IgG index = 0.86

IgG should under normal situations be almost totally excluded from CSF (blood:CSF ratio of >/= 500:1). Intrathecal production of IgG follows infiltration of the space by B-lymphocytes in demyelinating disorders.

Increase in CSF IgG can however be due to increased permeability form the plasma (dysfunctional barrier), increased plasma IgG concentration or intrathecal production. To correct for the former two, plasma IgG and serum albumin is used in an equation to get the above named index, which tries to isolate CSF IgG for the portion which was produced intrathecally.

The formula is: IgG index= (CSF IgG / Serum IgG) x (Serum Albumin / CSF Albumin). Units of measurement should be similar, at least for serum and CSF respectively.

Reference interval for CSF IgG index is 0.3 – 0.7. Ratios greater than 0.7 indicate increased intrathecal synthesis, as seen in more than 80% of cases of Multiple Sclerosis (MS) and other demyelinating disorders. False elevations occur in traumatic tap and SAH. CSF IgG index is more reliable when the CSF Albumin Index is normal (i.e. when the barrier function is not decreased, but obviously this is rarely the case, as inflammation leads to decreased barrier function).

CSF IgG synthesis rate

153 mg/day

The rate of intrathecal IgG synthesis can be estimated by the empirically derived Tourtellotte’s formula and a synthesis
rate of greater than 8 mg/day is found in most cases of multiple sclerosis. It is a more complex formula, with several constants and probably provides no additional information than the IgG index. (Ref: Tietz 6th Ed.)

Other Investigations

Investigations to this point include the following:

1. MRI brain and spine shows Longitudinal extensive transverse myelitis from the cervical to the lumbar level.

2. FBC and CEU was normal – Neutrophils were normal, lymphocyte count was 0.81.

3. Serologies were ANA, AdsDNA, AntiSm, Anti-Ro Positive. C3 and C4 were normal.

4. HIV, HBV, HCV serology was normal.

5. Serum AQP4 serology positive with a titre of 10

6. CSF: Protein-2.47, Gluc-1.4,P8, L37 R0, IgG index0.87, CLAT, GXP, Culture negative.

7. CD19: 250

8. CXR showed bilateral reticular nodular infiltrate and features of post of TB bronchiectasis

Final Diagnosis

Neuromyelitis Optica Spectrum Disorder

Take Home Message

CSF Glucose

Using a ratio of CSF to serum

glucose ratio of less than 0.4, an 80% sensitivity and 98%

specificity was found for distinguishing bacterial (n = 119)

versus aseptic cases (n = 97) of meningitis.

Donald P, Malan H, van der Walt A. Simultaneous
determination of cerebrospinal fluid glucose and blood
glucose concentrations in the diagnosis of bacterial
meningitis. J Pediatr 1983;103:3. – Referenced from Tietz Textbook of Clinical Chemistry 6th ed.

Recovery from meningitis results in recovery of glucose before CSF cell counts and Total Protein.

CSF glucose is typically normal in CSF viral infections, exceptions may include: Meningoencephalitis with Mumps, EV, HSV, HZV.

Leucocytes may also decrease CSF glucose – thus it may indicate a disease process rather than only bacterial infection.

Ratio of CSF:serum glucose has limited utility in neonates and in pts. with hyperglycemia.

CSF glucose <1.0 mmol/L is highly indicative of bacterial meningitis.

If intellectual disability, seizures and motor impairment is present along with low ratio, think of GLUT-1 transporter deficiency – then measure CSF lactate.

CSF Chemistry

As described above

Correcting total protein for Traumatic tap

The presence of CSF bleeding results in approximately 0.010 g of protein / L per 10^6 RBCs / L