Differentials
Primary central nervous system neoplasm
SIGNS / SYMPTOMS
Presentation may be identical, but less likely to include meningismus or fever.
Infectious source absent.
Presentation over a protracted period, with symptoms lasting several weeks to months, favours the diagnosis of neoplasm.
INVESTIGATIONS
White blood cell (WBC) count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) are generally not elevated.[41] Magnetic resonance imaging (MRI) more often demonstrates a heterogenous appearance. Magnetic resonance spectroscopy (MRS) lacks succinate, acetate, and amino acid elevations. Ultimately differentiated by surgical sampling of the lesion.
Metastatic lesion
SIGNS / SYMPTOMS
Rarely exhibits fever and meningismus. Infectious source absent.
History or signs and symptoms of the primary neoplasm may be present.
INVESTIGATIONS
CT chest, abdomen, and pelvis, or possibly bone scan or mammogram, reveal the primary lesion in most cases. Occasionally presents as a cryptogenic lesion. Tissue diagnosis by surgical biopsy or resection is definitive.
Recurrent tumour/radiation necrosis in a post-surgical patient
SIGNS / SYMPTOMS
Time course generally distinguishes radiation necrosis, which occurs after a full course of radiotherapy.
Often asymptomatic. Fever and meningeal signs absent.
INVESTIGATIONS
Elevated WBC count more indicative of abscess unless the patient remains on corticosteroids.
MRI generally shows fluid in the surgical cavity that is consistent with a purulent collection in brain abscess.
Magnetic resonance spectroscopy (MRS) lacks peaks associated with metabolic activity in radiation necrosis.
If suspicion persists, surgical re-exploration is indicated.
Multiple sclerosis (MS)
SIGNS / SYMPTOMS
Longer history of protean neurological symptoms.
Fevers and meningismus absent.
Occurs in characteristic population.
Presence of specific signs: Lhermitte's sign (transient electric-like shocks extending down the spine), Uhthoff's sign (episodic transient obscuration of vision).
INVESTIGATIONS
Cerebrospinal fluid (CSF) analysis, if lumbar puncture (LP) is performed, shows characteristics of MS.
MRI demonstrates exclusively white matter lesions that fluctuate over time and vary with their degree of enhancement.
Acute disseminated encephalomyelitis
SIGNS / SYMPTOMS
History of prior inflammatory event or vaccination.
More common in children and patients from tropical climates.
INVESTIGATIONS
MRI shows lesion restricted to white matter. Evoked potentials consistent with demyelination.
Ischaemic stroke
SIGNS / SYMPTOMS
Lack of fever and meningeal signs. Presents as sudden neurological deficit that is relatively stable afterwards. Headache is rare.
INVESTIGATIONS
Lack of elevated ESR, CRP, WBC count. MRI rarely exhibits contrast enhancement except for pseudolaminar necrosis. Diffusion-weighted images on MRI show characteristic findings depending on timing of study.
Limited to a single vascular distribution.
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