McDonald criteria

Key takeaways

McDonald criteria belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect McDonald criteria to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of McDonald criteria from memory before moving on to harder problems.

Reference excerpt

The McDonald criteria are diagnostic criteria for multiple sclerosis (MS). These criteria are named after neurologist W. Ian McDonald who directed an international panel in association with the National Multiple Sclerosis Society (NMSS) of America and recommended revised diagnostic criteria for MS in April 2001. These new criteria intended to replace the Poser criteria and the older Schumacher criteria. They have undergone revisions in 2005, 2010 and 2017. They maintain the Poser requirement to demonstrate "dissemination of lesions in space and time" (DIS and DIT) but they discourage the previously used Poser terms such as "clinically definite" and "probable MS", and propose as diagnostic either "MS", "possible MS", or "not MS". The McDonald criteria maintained a scheme for diagnosing MS based solely on clinical grounds but also proposed for the first time that when clinical evidence is lacking, magnetic resonance imaging (MRI) findings can serve as surrogates for dissemination in space (DIS) and/or time (DIT) to diagnose MS. The criteria try to prove the existence of demyelinating lesions, by image or by their effects, showing that they occur in different areas of the nervous system (DIS) and that they accumulate over time (DIT). The McDonald criteria facilitate the diagnosis of MS in patients who present with their first demyelinating attack and significantly increase the sensitivity for diagnosing MS without compromising the specificity. The McDonald criteria for the diagnosis of multiple sclerosis were revised first in 2005 to clarify exactly what is meant by an "attack", "dissemination" and a "positive MRI", etc. Later they were revised again in 2017. McDonald criteria are the standard clinical case definition for MS and the 2010 version is regarded as the gold standard test for MS diagnosis.

Diagnostic Criteria

They discourage the previously used terms such as "clinically definite" and "probable MS", and propose as diagnostic variants like "MS", "possible MS", or "not MS", though these terms change between revisions. As of 2017 revision The term 'possible MS' was added for people with a typical clinically isolated syndrome who did not meet the criteria.

Criticism Pathology is generally regarded as the gold standard in defining different forms of inflammatory demyelinating diseases. Specificity of the McDonald criteria is low due to the fact that the nature of the lesions is not considered, but only their dissemination. None of the criteria are MS-specific. In order to reduce false positives, McDonald et al. propose that their criteria should be applied only after any other disease has been ruled out. In 2008 a consensus was developed for differential diagnosis. Another criticism of the McDonald criteria is that the definition of "lesions typical of MS" is unclear; a 2013 review identified the following characteristics: specific cell morphology shown by hematoxylin, demyelination shown by Luxol fast blue, macrophage appearance by KiM1P or CD68, damage to the axons shown by Bielschowsky stain, astrocytopathy shown by glial fibrillary acidic protein, and different lymphocyte subtypes, reacting to CD3, CD4, CD8, CD20 and CD138. The sensitivity of McDonald criteria is low with regard to pathologically defined MS because around 25% of MS cases are silent MS cases. McDonald criteria have been shown to have a low sensitivity and specificity (with respect to the pathological presence of lesions) in Asiatic populations. They have good predictive quality (with respect to CIS [clinically isolated syndrome] to CDMS [Clinically Definite Multiple Sclerosis] conversion) when evaluated in non-selected populations.

Comparison of McDonald versions Currently there is not too much information comparing the sensibility and specificity of different McDonald versions against autopsy. Some reports have used Poser "CDMS" delayed diagnosis (during a two-year follow-up) as milestone to evaluate these parameters. It seems that 2017 revision has higher sensitivity (85 vs. 30% and 85 vs. 41%) and lower specificity (33 vs. 63% and 63 vs. 85%) compared to the 2010 revisions and Poser CDMS, at two years follow-up.

2010 Revisions In 2010, the International Panel on Diagnosis of MS met in Dublin, Ireland for a third time to discuss and revise the McDonald diagnostic criteria. Reasons for revisions to the criteria included the simplification of demonstration of CNS lesions in space and time via imaging, and to address criticisms that the previous criteria did not appropriately apply to Asian populations. One study has suggested that the new criteria allow a faster diagnosis, but with slight sacrifice in accuracy.

Revised Diagnostic Criteria (2010)

2017 revision The last revision (as of 2018) is the 2017 revision. It has been reported to improve sensibility up to an 82% (respect around 8 years CIS to MS conversion, retrospectively evaluated). The 2017 revision predicted 86.8% of positives in the follow-up using as reference the 2010 criteria after a follow-up of 3.8 ± 2.9 years. No reduction in specificity was reported. The 2017 revision tries to accelerate the diagnosis without risking specificity. The new recommendations include:

First of all, probably the most polemical change, a patient with CIS (only one demyelinating lesion) can now be diagnosed as MS if an MRI shows dissemination in space (DIS). In these cases dissemination in time (DIT) can be substituted by a laboratory testing of oligoclonal bands. Second, both symptomatic and asymptomatic lesions can be considered for showing DIS and DIT Third, also cortical lesions can be used to show DIS. Fourth, also for PPMS cortical and asymptomatic lesions can be used in diagnosis.

Future directions

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with McDonald criteria

Start with the simplest possible case. Write down what McDonald criteria claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to McDonald criteria before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about McDonald criteria ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of McDonald criteria

In research: McDonald criteria appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses McDonald criteria in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: McDonald criteria is common in secondary-school and first-year university syllabi. It links to neighbouring topics Autoimmune diseases, Multiple sclerosis, Neurological disorders, so understanding it makes those chapters shorter.
In everyday life: Look for McDonald criteria outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study McDonald criteria in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what McDonald criteria means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain McDonald criteria out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is McDonald criteria in simple terms?

The McDonald criteria are diagnostic criteria for multiple sclerosis (MS). These criteria are named after neurologist W.

Why does McDonald criteria matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study McDonald criteria?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on McDonald criteria.