When to perform a lumbar puncture (LP) in a patient with fever of unknown origin (FUO)?

From the Guidelines

A lumbar puncture should be performed in a patient with fever of unknown origin when there is suspicion of central nervous system infection, particularly meningitis or encephalitis, after obtaining blood cultures but before administering antibiotics if possible, as indicated by the most recent guidelines 1. The procedure is indicated when a patient presents with fever accompanied by neurological symptoms such as headache, neck stiffness, altered mental status, or focal neurological deficits.

• The decision to perform a lumbar puncture should be based on clinical assessment rather than CT scanning, unless there are signs suggestive of increased intracranial pressure or a space-occupying lesion, such as papilledema on fundoscopic examination 1.
• In patients with suspected encephalitis, an early CT scan has two clear roles: suggesting the diagnosis of viral encephalitis and indicating an alternative diagnosis, but unselected CT scanning of all patients before an LP can cause unnecessary delays for the majority of patients, in whom there are no contraindications to an immediate LP 1.
• The procedure involves inserting a needle between the L3-L4 or L4-L5 vertebral spaces to collect cerebrospinal fluid for analysis of cell count, glucose, protein, culture, and other specialized tests as indicated.
• This diagnostic procedure is crucial as it can identify the causative organism and guide appropriate antimicrobial therapy, potentially saving the patient's life in cases of bacterial meningitis, as emphasized by the guidelines for evaluation of new fever in critically ill adult patients 1.
• In immunocompromised patients with fever, a lower threshold for performing a lumbar puncture may be appropriate due to their increased risk of opportunistic CNS infections, as suggested by the management guidelines for suspected viral encephalitis in adults 1.

From the Research

Indications for Lumbar Puncture in Fever of Unknown Origin

• Fever of unknown origin (FUO) is a condition where a patient has an elevated body temperature, but the cause of the fever is not known despite extensive diagnostic evaluation 2.
• Lumbar puncture (LP) is a diagnostic procedure that involves collecting a sample of cerebrospinal fluid (CSF) to help diagnose various conditions, including infections and inflammation of the central nervous system (CNS) 3, 4.
• The decision to perform a lumbar puncture in a patient with FUO depends on various factors, including the presence of symptoms such as headache, neck stiffness, and altered mental status 5, 6.

Clinical Features and Laboratory Parameters

• Patients with FUO who present with headache and fever may require a lumbar puncture to rule out viral meningitis or other CNS infections 6.
• Clinical features such as neck stiffness, vomiting, and C-reactive protein level ≤ 1.291 mg/dL can be used to develop a scoring system to diagnose viral meningitis and identify patients who should receive lumbar punctures 6.
• Laboratory parameters such as CSF biochemical tests (protein, glucose, and lactate levels) and microscopy can provide a prompt insight into the infective etiology and inform treatment and further diagnostic testing strategies 3.

Timing of Lumbar Puncture

• There is no specific guideline on the optimal timing of lumbar puncture in patients with FUO, but it is generally recommended to perform the procedure as soon as possible after the diagnosis of FUO is made, especially if there are symptoms suggestive of CNS infection 3, 5.
• Antimicrobial pretreatment may affect the CSF results, and therefore, it is recommended to perform the lumbar puncture before starting antibiotic therapy whenever possible 3.