Apply only to an eligible clinical presentation, name the evidence for each logical gate, and keep the 2017 and 2024 rules separate. A matching MRI phrase is never enough to diagnose MS.
{
"categories": [
{
"outcome_code": "periventricular",
"role": "DIS_region",
"region": "periventricular"
},
{
"outcome_code": "cortical-juxtacortical",
"role": "DIS_region",
"region": "cortical_or_juxtacortical"
},
{
"outcome_code": "infratentorial",
"role": "DIS_region",
"region": "infratentorial"
},
{
"outcome_code": "spinal-cord",
"role": "DIS_region",
"region": "spinal_cord"
},
{
"outcome_code": "DIS",
"role": "criterion_state",
"meaning": "dissemination_in_space_demonstrated"
},
{
"outcome_code": "DIT",
"role": "criterion_state",
"meaning": "dissemination_in_time_demonstrated"
},
{
"outcome_code": "CSF-OCB",
"role": "criterion_mechanism",
"meaning": "CSF_specific_oligoclonal_bands_can_substitute_for_DIT_in_the_eligible_attack_onset_pathway"
},
{
"outcome_code": "attack-onset-MS",
"role": "diagnostic_state",
"meaning": "2017_attack_onset_criteria_fulfilled_and_no_better_explanation"
},
{
"outcome_code": "possible-MS",
"role": "diagnostic_state",
"meaning": "typical_CIS_suggests_MS_but_2017_criteria_are_incomplete"
},
{
"outcome_code": "not-MS",
"role": "diagnostic_state",
"meaning": "another_diagnosis_better_explains_the_presentation"
},
{
"outcome_code": "PPMS",
"role": "diagnostic_state",
"meaning": "2017_progression_from_onset_pathway_fulfilled"
}
],
"applicability": {
"this_version": "2017_McDonald_criteria_only",
"primary_population": "A patient with a typical clinically isolated syndrome caused by a focal or multifocal inflammatory demyelinating CNS event, or a patient with objectively documented progression from onset.",
"mandatory_final_condition": "There is no better explanation for the clinical presentation and objective evidence supports the diagnosis.",
"not_designed_for": [
"screening_asymptomatic_people",
"diagnosing_MS_from_nonspecific_white_matter_lesions_alone",
"differentiating_every_MS_mimic",
"choosing_or_monitoring_disease_modifying_treatment"
]
},
"attack_definition": {
"clinical_event": "A monophasic focal or multifocal CNS disturbance typical of inflammatory demyelination, developing acutely or subacutely and lasting at least 24 hours, with or without recovery, in the absence of fever or infection.",
"objective_evidence_rule": "At least one attack must be supported by objective findings. Historical symptoms without contemporaneous or residual objective evidence require caution.",
"separation_for_two_attacks": "Two attacks used to establish DIT are separated by at least one month."
},
"MRI_DIS_2017": {
"rule": "At least one T2-hyperintense lesion characteristic of MS in at least two of the four 2017 CNS regions.",
"regions": [
"periventricular",
"cortical-juxtacortical",
"infratentorial",
"spinal-cord"
],
"symptomatic_lesions": "Symptomatic and asymptomatic lesions can count toward DIS.",
"cortical_rule": "Cortical and juxtacortical lesions share one regional category; multiple lesions within that single region still contribute only one region toward the two-region rule.",
"optic_nerve_2017_exclusion": "Optic-nerve involvement is not a fifth DIS region in the 2017 criteria, and an optic-nerve lesion causing the presenting optic neuritis is not used to fulfill 2017 DIS.",
"vascular_risk_caution": "For older patients or those with vascular risk factors, the panel advised seeking a higher burden of periventricular lesions and stronger corroborating evidence rather than relying on one nonspecific lesion."
},
"MRI_DIT_2017": {
"alternatives": [
"simultaneous_presence_of_gadolinium_enhancing_and_non_enhancing_lesions_at_any_time",
"new_T2_hyperintense_or_gadolinium_enhancing_lesion_on_follow_up_compared_with_baseline_regardless_of_baseline_timing"
],
"symptomatic_lesions": "Symptomatic and asymptomatic lesions can count toward MRI DIT in 2017.",
"clinical_alternative": "A second clinical attack can demonstrate DIT."
},
"CSF_OCB_2017": {
"laboratory_definition": "Qualitative demonstration of at least two CSF-specific oligoclonal IgG bands indicating intrathecal synthesis, assessed with paired serum and CSF using an appropriate standardized method.",
"substitution_rule": "In a typical CIS with clinical or MRI DIS, no better explanation, and no atypical CSF findings, CSF-specific OCBs can substitute for demonstration of DIT.",
"semantic_guard": "OCBs do not demonstrate DIT per se; they are an allowed substitute in the eligible 2017 attack-onset pathway.",
"atypical_CSF_warning": [
"markedly_elevated_protein",
"pleocytosis_above_50_cells_per_mm3",
"neutrophils",
"eosinophils",
"atypical_cells"
],
"specificity_guard": "CSF-specific OCBs support but are not specific for MS; alternative inflammatory, infectious and immune causes still require assessment."
},
"attack_onset_pathway": [
{
"presentation": "two_or_more_attacks_and_objective_evidence_of_two_or_more_lesions",
"additional_data": "none_for_DIS_or_DIT",
"output_if_no_better_explanation": "attack-onset-MS"
},
{
"presentation": "two_or_more_attacks_and_objective_evidence_of_one_lesion_plus_clear_historical_attack_in_a_different_location",
"additional_data": "none_for_DIS_or_DIT_but_at_least_one_attack_must_have_objective_support",
"output_if_no_better_explanation": "attack-onset-MS"
},
{
"presentation": "two_or_more_attacks_and_objective_evidence_of_one_lesion",
"additional_data": "DIS_by_an_attack_at_another_CNS_site_or_MRI_DIS",
"output_if_fulfilled_and_no_better_explanation": "attack-onset-MS"
},
{
"presentation": "one_attack_and_objective_evidence_of_two_or_more_lesions",
"additional_data": "DIT_by_second_attack_or_MRI_DIT_or_eligible_CSF_OCB_substitution",
"output_if_fulfilled_and_no_better_explanation": "attack-onset-MS"
},
{
"presentation": "one_attack_and_objective_evidence_of_one_lesion",
"additional_data": "both_DIS_by_second_site_attack_or_MRI_and_DIT_by_second_attack_MRI_or_eligible_CSF_OCB_substitution",
"output_if_fulfilled_and_no_better_explanation": "attack-onset-MS"
}
],
"progression_from_onset_pathway": {
"duration_gate": "At least one year of disability progression, determined retrospectively or prospectively, independent of clinical relapse.",
"plus_two_of_three": [
{
"component": "brain_DIS",
"rule": "at_least_one_T2_lesion_in_at_least_one_of_periventricular_cortical_or_juxtacortical_or_infratentorial_regions"
},
{
"component": "spinal_cord_DIS",
"rule": "at_least_two_T2_spinal_cord_lesions"
},
{
"component": "CSF",
"rule": "CSF_specific_oligoclonal_bands"
}
],
"symptomatic_lesions": "No distinction between symptomatic and asymptomatic MRI lesions is required.",
"output_if_fulfilled_and_no_better_explanation": "PPMS"
},
"diagnostic_state_rules": {
"criteria_fulfilled": "Use attack-onset-MS or PPMS only when its complete pathway is met and no better explanation remains.",
"incomplete_typical_CIS": "Use possible-MS when MS is suspected because of a typical CIS but the 2017 criteria are not completely met.",
"better_explanation": "Use not-MS when another diagnosis better explains the presentation; failure to fulfill the criteria alone is not automatically not-MS."
},
"misdiagnosis_guard": [
"The criteria were designed to identify MS in a population with a typical CIS after competing diagnoses were deemed unlikely; they are not a stand-alone differential-diagnosis engine.",
"Integrate history, neurologic examination, lesion morphology and distribution, laboratory findings and follow-up; a text-mining agent must not turn isolated MRI phrases into a diagnosis.",
"If the presentation is non-classical, evidence is insufficient, or tests are negative or atypical, defer a definitive label and obtain appropriate brain or spinal MRI, CSF evaluation and specialist review.",
"Do not infer a clinical attack, objective lesion, fever exclusion, infection exclusion, progression duration or CSF result from imaging alone."
],
"version_boundary": {
"current_revision_notice": "The 2024 McDonald criteria were published in September 2025 and substantially revised the 2017 framework.",
"do_not_backport_into_2017": [
"optic_nerve_as_fifth_DIS_site",
"kappa_free_light_chain_index_as_CSF_alternative",
"central_vein_sign",
"paramagnetic_rim_lesions",
"selected_diagnosis_without_DIT",
"selected_RIS_diagnosis",
"unified_relapsing_and_progressive_framework"
],
"safe_use": "Use this map only when the caller explicitly requests the 2017 historical criteria. For a current diagnosis, consult and implement the 2024 criteria rather than combining versions ad hoc."
},
"output_contract": [
"requested_version_and_currency_warning",
"typical_or_atypical_presentation",
"number_of_clinical_attacks_and_objective_lesion_sites",
"four_region_MRI_DIS_evidence_with_each_region_named",
"MRI_or_clinical_DIT_evidence",
"CSF_specific_OCB_status_and_whether_used_as_DIT_substitute",
"attack_onset_or_progression_from_onset_pathway",
"criteria_met_possible_MS_or_better_explanation_state",
"missing_inputs_and_differential_diagnosis_caveat"
],
"missing_input_behavior": [
"If lesion morphology or exact CNS region is not established, do not count that lesion toward DIS.",
"If enhancement status or a comparable baseline scan is unavailable, do not claim MRI DIT unless another valid DIT route is documented.",
"If OCBs are reported without confirmation that they are CSF-specific or without assessment for atypical CSF findings, do not use them automatically as the DIT substitute.",
"If the presentation is not a typical CIS and the progressive-from-onset pathway is not established, do not apply the 2017 algorithm as if eligibility were proven.",
"If a current-version request is ambiguous, return the 2024-version warning and request version confirmation rather than silently using 2017."
],
"interpretation_limits": [
"The McDonald criteria establish a diagnostic framework; they do not grade disease severity, predict an individual's course, or choose treatment.",
"DIS and DIT are logical criteria, not counts to add into a severity score.",
"An MRI report can supply lesion evidence but cannot alone establish the complete clinical diagnosis or exclusion of a better explanation."
],
"source_locator": "Thompson et al., Lancet Neurol 2018;17:162-173, PMID 29275977, DOI 10.1016/S1474-4422(17)30470-2, accepted manuscript Panels 1 and 3-6 and Table 1; ECTRIMS McDonald Diagnostic Criteria page and Montalban et al., Lancet Neurol 2025, PMID 40975101, DOI 10.1016/S1474-4422(25)00270-4 for the newer-version boundary."
}