1. This station tests your knowledge of both the normal values of various components of cerebrospinal fluid (CSF) and also your ability to make a differential diagnosis of a condition purely from a set of CSF results.
2. Obviously, the most important knowledge to have for this station is the normal values. The most important of these are given in the table below (NB these are for adults only):
| Value | Normal Range |
|---|---|
| Appearance | Clear & colourless |
| White Cells | 0 - 5 x 106 per litre (all lymphocytes with no neutrophils) |
| Red Cells | 0 - 10 x 106 per litre |
| Protein | 0.2 - 0.4 grammes per litre (or less than 1% of the serum protein concentration) |
| Glucose | 3.3 - 4.4 mmol per litre (or ≥ 60% of a simultaneously derived plasma glucose concentration) |
| pH | 7.31 |
| Pressure | 70 - 180 mmH2O |
3. The next step in succeeding in this station is to systematically take the examiner through the results which you have been given. Just start at the top and simply comment whether each result is normal or not. If any result is abnormal, you should comment whether it is slightly or very deranged.
4. Once you have done this, you will most likely be asked to make a differential diagnosis based upon the results you have just seen. A number of conditions give deranged CSF readings and so again knowledge of which conditions affect the different values is vital. The changes in various conditions are given below:
| Condition | Appearance | White Cells | Red Cells | Protein | Glucose |
|---|---|---|---|---|---|
| Bacterial Meningitis | Cloudy & Turbid | Raised neutrophils | N | H or VH | VL |
| Viral Meningitis | N | Raised lymphocytes | N | N or H | N or L |
| Tuberculous Meningitis | N or slightly cloudy | Raised lymphocytes | N | H or VH | VL |
| Subarachnoid Haemorrhage | Usually blood stained | N | VH | N or H | N or L |
| Guillan-Barré Syndrome | N | N | N | H (only after 1 week) | N or L |
| Multiple Sclerosis | N | Raised lymphocytes | N | H | N |
VL = Very Low
L = Low
N = Normal
H = High
VH = Very High
5. Although this may seem quite daunting, you will soon start to recognise obvious patterns. Plus you are more likely to be asked about the more common conditions such as bacterial and viral meningitis.
6. Finally, if the condition is meningitis, whatever kind, you are likely to be asked for a causative organism so make sure you know the common causes of meningitis for varying age groups as well as the treatment.
© Matthew Green and Laura Henderson 2006.