In 1976, Richard Dawkins, in The Selfish Gene,1 introduced the term ‘meme’ to describe a verbally transmitted cultural idea that could replicate in a way comparable to a gene. The term itself is a shortening of the Ancient Greek term ‘mineme’, meaning to copy or imitate. The concept that ideas can replicate and be transmitted seems a good one; memes on the internet can certainly ‘go viral’ (figure 1) and fittingly, the very word meme has become a meme.

• Download figure
• Open in new tab
• Download powerpoint

Figure 1

The ALS ice bucket challenge was one of the most successful memes of 2014, raising over $100 million. The Oxford MND team are pictured taking the challenge (photo courtesy Kevin Talbot, 3rd from right).

When a new diagnostic category is first described, the idea can spread. The first phase of such a diagnostic meme is the condition's description, the definition of terms. After James Parkinson described ‘The shaking palsy’ in 1817,2 Charcot later referred to it as Parkinson's disease3 and with time the condition became increasingly well defined. The diagnostic meme replicates, the diagnosis spreads, yet inevitably sometimes the diagnosis will be wrong or overlooked. Huw Morris and Khalid Ali clarify for us these mimics and chameleons of Parkinson's disease (see page 14).

Posterior cortical atrophy is a surprisingly recently recognised entity, being described by Benson in 1988.4 Remarkably, in its diagnostic evolution, its most widely recognised description is ‘The man who mistook his wife for a hat’, published by Oliver Sacks three years earlier in 1985. With hindsight, and with the meme now widely disseminated, Sacks' patient with progressive visual agnosia but relative preservation of other areas of higher function is readily recognisable as having posterior cortical atrophy. We have an update on these clinical manifestations by Shin Beh and colleagues (see page 5). This review will also be free to access online. Jonathan Schott, who reviewed the paper for us, emphasises the importance of confident recognition of specific underlying pathological processes of dementia—and the difficulties of identifying pathology from clinical phenotype—as new treatments for neurodegenerative conditions increasingly beckon (see page 2).

Sometimes a diagnostic meme takes hold and dominates the diagnosis. Such an idea is the recognition of longitudinally-extensive transverse myelitis as a characteristic feature of neuromyelitis optica: this provides the context for a couple of our case reports describing important alternative causes of extensive cord lesions. Richard Sylvester and colleagues (see page 49) describe this in a patient with common variable immunodeficiency syndrome, something easily mistaken for sarcoidosis, and Stephan Hinze and colleagues (see page 60) report similar longitudinal cord changes in CADASIL.

On the other side of the coin there are rarer diagnoses of which we may hardly be aware: their diagnostic memes have not replicated. We hope that publishing such cases will help to spread these memes, especially if they have practical implications. First, we have two patients with encephalopathies that were challenging to diagnose: Michel Tchan and colleagues (see page 45) describe one where the diagnosis indicated useful treatment, and Michael Flower and colleagues (see page 56) describe another where certain treatments must be avoided. Second, there are two patients with visual problems: Khalid Ali describes a patient with a uniocular field defect from a cortical lesion—and explains how this occurs (see page 53)—and Susan Mollan and colleagues (see page 72) describe a patient with pseudotumour cerebri caused by vitamin A supplements. Claudio de Gusmao et al (see page 42) describe a dramatic and dynamic complication of shunting and David Werring's team (see page 74) illustrate some radiological features of cerebral amyloid angiopathy.

We have the next in Shelley Renowden's series on imaging, this time of the pituitary (see page 26) and there is a clinicopathological conference (discussant Martin Turner who also appears in the photo) to challenge your thinking (see page 63). Huntington's disease is the archetype for a late-onset dominantly inherited neurodegenerative condition and is the disorder most commonly used to frame the issues surrounding genetic testing. We are pleased to publish the European Huntington's Disease Network's guidance on genetic testing in Huntington's disease (see page 80).

The Neurological Book Club (see page 85) revisits Parkinson's disease: ‘Family Matters’ again takes the patient and family perspective but starkly contrasts with that of Michael J. Fox, discussed last year. Lastly, A fo Ben scours the rest of the medical press for memes that have still to spread (see page 86).