Professional and Linguistic Assessments Board (PLAB) Practice Exam

When is the earliest that a lumbar puncture should be done after a headache?

1. 6 hours

2. 12 hours

3. 24 hours

4. 48 hours

The correct answer is: 12 hours

A lumbar puncture is a critical diagnostic procedure, especially in patients with suspected conditions such as meningitis or other central nervous system pathologies. The timing of this procedure relative to the onset of symptoms, such as a headache, is important for several reasons. The recommendation to wait at least 12 hours after the onset of a headache before performing a lumbar puncture is primarily based on the need to allow for the resolution of acute headache symptoms and to assess for any evolving clinical signs that may influence the diagnosis. This waiting period can help in determining whether the headache is primary or secondary to another underlying condition that might be contraindicated for lumbar puncture. Performing the procedure too soon might lead to difficulties in interpretation of the cerebrospinal fluid findings, especially if there is a chance that the headache could be due to a condition that may inadvertently be worsened by the puncture itself. In cases, such as those involving intracranial hypertension or mass effect, it is essential to have a clear understanding of the clinical presentation before proceeding. In summary, conducting a lumbar puncture after a 12-hour interval allows for a more accurate assessment of the patient's condition and increases the reliability of the results obtained from the procedure.