Coexistence of Neurosarcoidosis and Neuromyelitis Optica Spectrum Disorder (NMOSD)
A patient can have neurosarcoidosis and neuromyelitis optica spectrum disorder (NMOSD) in the same clinical course, although this combination is uncommon and diagnostically challenging. [1] Neurosarcoidosis can also mimic NMOSD, including presentation with optic neuritis or myelitis and sometimes with reported aquaporin-4 (AQP4) antibody positivity, which can initially resemble NMOSD. [2], [3]
Diagnostic Implications of Overlapping Presentations
NMOSD is classically characterized by optic neuritis and/or longitudinally extensive transverse myelitis, with AQP4-IgG or MOG-IgG supporting immune-mediated phenotypes. [4] Neurosarcoidosis is a granulomatous inflammatory disorder of the nervous system that can produce optic nerve and spinal cord involvement. [2], [3] The clinical overlap between inflammatory myelitis syndromes requires demonstration of sarcoidosis (typically with systemic and/or tissue evidence) in addition to confirmation of an NMOSD phenotype when both conditions are suspected. [2], [3], [5]
Evidence Supporting Possible Co-Occurrence
Case documentation exists describing a patient with sarcoidosis and neuromyelitis optica/Devic-type disease in the setting of optic neuritis, supporting potential coexistence rather than pure mimicry. [1] Additional case series and case reports describe neurosarcoidosis patients in whom AQP4 antibody positivity occurred and led to diagnostic consideration of NMOSD, emphasizing that AQP4-positive results may not always indicate primary NMOSD. [2], [3]
Evidence of Neurosarcoidosis Mimicking NMOSD
Probable neurosarcoidosis presenting as cervicomedullary myelitis with AQP4-IgG positivity has been reported, with the initial presentation raising concern for NMOSD. [2] Three cases of neurosarcoidosis with positive AQP4 antibody requiring differentiation from NMOSD spectrum disorder have been reported. [3] These reports support that neurosarcoidosis can produce NMOSD-like clinical phenotypes and can confound antibody-based diagnosis. [2], [3]
Practical Diagnostic Framework When Both Conditions Are Suspected
High-priority diagnostic steps include confirmation of sarcoidosis activity or presence of systemic granulomatous disease. [3], [5] High-priority diagnostic steps include careful NMOSD antibody interpretation in the context of imaging, cerebrospinal fluid profile, and clinical phenotypes. [2], [3] Tissue diagnosis can be important when antibody results and clinical phenotype are discordant with a single unifying diagnosis. [3], [5]
Common Pitfalls in Interpreting AQP4 Antibody Positivity
Assuming that any AQP4 positivity automatically confirms NMOSD can be incorrect when neurosarcoidosis presents with AQP4 antibody positivity. [2], [3] Anchoring on an antibody result without full consideration of neurosarcoidosis can delay sarcoid-directed evaluation and may lead to incomplete diagnostic classification. [2], [3]
Treatment-Relevant Consequences of Diagnostic Uncertainty
When coexistence versus mimicry is unresolved, treatment planning should reflect the need to control neuroinflammation while concurrently pursuing definitive classification of sarcoidosis versus NMOSD. [2], [3] Coherence of therapy with the final diagnosis is important because sarcoidosis-directed evaluation and NMOSD prevention strategies differ in long-term disease management. [1], [2], [3]