What tests best rule out neurosarcoidosis before considering aHSCT?

No single test rules out neurosarcoidosis. The best you can do is build a case from several tests, and even then a negative biopsy leaves doubt.

Nothing in this retrieval measured how well any test excludes neurosarcoidosis before aHSCT. That question is not answered here, and I will not pretend it is. What the records do show is the shape of the diagnostic problem.

MRI has the clearest role. In one 2025 case, T1, T2, FLAIR, DWI and post-contrast sequences showed nodular enhancement along the brain coverings and along the optic nerves, and the MRI guided which tissue to biopsy [2]. A 2004 series found MRI abnormalities in all seven patients, with meningeal and brain-tissue involvement [3]. The review describes the same pattern: inflammation at the base of the brain, nodular thickening, and nerve involvement [5]. MS does not usually look like that, which is the whole point of imaging it.

CSF helps less than people think. ACE levels in spinal fluid were raised in only some suspected cases and were not clearly different from controls [1]. White cells and protein can be up, but nonspecifically [2][3]. Oligoclonal bands are common in MS, at 95% in one review [4], so bands alone cannot separate the two.

The only test that actually confirms sarcoidosis is a biopsy showing non-caseating granulomas, which this case achieved [2] and which the review names as the defining histology [5]. A chest scan showing enlarged lymph nodes supports it [2]. Before aHSCT, I would want contrast MRI of brain and spine, CSF with cell count and protein and ACE, a chest image, and a biopsy of any accessible lesion. If nothing is accessible, that is a genuine gap.

My call: do the full workup, but understand that no test in this evidence set reliably excludes neurosarcoidosis, and a negative spinal fluid does not settle it. Confidence: low, because the exact exclusion question was not studied in these records.