The menagerie of neurology

Summary

Neurology is a field known for “eponymophilia.” While eponym use has been a controversial issue in medicine, animal-related metaphoric descriptions continue to flourish in neurologic practice, particularly with the advent of neuroimaging. To provide practicing and trainee neurologists with a useful reference for all these colorful eponyms, we performed a literature review and summarized the various animal eponyms in the practice of neurology (and their etiologic implications) to date. We believe that the ability to recognize animal-like attributes in clinical neurology and neuroradiology may be attributed to a visual phenomenon known as pareidolia. We propose that animal eponyms are a useful method of recognizing clinical and radiologic patterns that aid in the diagnostic process and therefore are effective aidesmémoire and communicative tools that enliven and improve the practice of neurology.

While medicine and science have a tradition of eponyms (naming discoveries after scientists, physicians, patients, geographic locations, mythical beings, etc.), neurology is particularly famous (or infamous, depending on your views) for “eponymophilia.”1

While most agree on repudiating eponyms that honor war criminals,1 the debate for and against eponym use continues. Opponents prefer more descriptive names (e.g., extensor plantar response, rather than the Babinski sign). Supporters argue that eponyms are useful, linguistically economical representations of convoluted, unwieldy terminology (e.g., Sneddon syndrome, instead of idiopathic livedo reticularis with cerebrovascular accidents).2 Some propose that eponyms add character, color, flavor, and dimension to the practice of neurology; others malign “eponymophilia” for engendering an overly complicated and cabalistic image of the specialty.2,3 Despite this controversy, zoologically inspired metaphorical descriptions continue to flourish in the luxuriant “eponymic forest of neurologic disorders,”3 and even more so with the advent of neuroimaging (table).

Table-a Summary of diagnostic implications of animal-inspired eponyms in neurology

Table-b Summary of diagnostic implications of animal-inspired eponyms in neurology

A word of caution: while animal-inspired eponyms are a pithy way of describing clinical and neuroradiologic signs, discretion should be exercised when using these terms in front of patients. Most understand that we intend no insult, but there are those who would perceive that we are making sport of their illness. As such, the honest, open discussion of such strategies that are utilized in order to augment clinical acumen cannot be overemphasized.

Animals at the bedside

Hands

The simian crease (a single transverse palmar crease) may be a normal finding or may be found in various genetic syndromes (classically trisomy 21). The ape hand may be seen in median neuropathy, where thenar atrophy leads to recession of thumb-associated metacarpals to the plane of the other metacarpals, as a consequence of the unopposed actions of the extensor pollicis longus and adductor pollicis.4 Arachnodactyly (spider fingers) refers to abnormally long and slender fingers; it is typically found in fibrillinopathies like Marfan syndrome, Ehlers-Danlos syndrome, and homocystinuria.5

Gait

Animal-inspired metaphors are especially popular when characterizing disorders of locomotion. Proximal lower extremity weakness results in the appearance of waddling, hence the term duck gait.6 In contradistinction, weakness of the anterior tibialis and peroneal muscle groups culminates in footdrop, compelling the patient to excessively flex the hip and lift the knee to keep the foot clear of the ground (termed the cock or equine gait).6,7

Axial dystonia may cause increasing lumbar lordoscoliosis while walking, inducing bizarre truncal postures with the hip bulging backwards and sideways accompanied by compensatory turning of the shoulders and neck with the head held vertically; this progressive lordotic dysbasia is succinctly referred to as the dromedary gait.6

Head and neck

The tigroid fundus is a normal fundoscopic finding in which lesser amounts of pigment in the retinal pigment epithelium allow visualization of streaks of underlying normal choroidal pigmentation. When a saccade terminates with a burst of flutter, this is called flutter dysmetria or fishtail nystagmus; causes include paraneoplastic disorders or metabolic-toxic states.7

Almost all clinicians are familiar with raccoon eyes (bilateral periorbital ecchymoses) signifying the presence of a basilar skull fracture.8–10 Not many, however, are aware that raccoon eyes have been observed in many other conditions, including amyloidosis,11,12 neuroblastoma,13–16 multiple myeloma,17 Kaposi sarcoma,18 following vigorous sneezing or coughing,19,20,e1 continuous positive airway pressure use,^e2 dengue fever–induced thrombocytopenia,^e3 trigeminal autonomic cephalgia,^e4 migraine,^e5 and following rhinoplasty.^e6

The unmistakable physiognomy of myotonic dystrophy imparts an uncanny resemblance to the hatchetfish (Argyropelecus species), hence the term hatchet face. This conspicuous morphologic manifestation may be combined with sternomastoid weakness and atrophy associated with exaggerated forward neck curvature, reminiscent of a swan neck.7

Tongue

The term fly catcher tongue aptly describes the recurrent back-and-forth darting movements of the tongue in Huntington disease.^e7 Substantially more inconspicuous is the galloping tongue phenomenon, most commonly associated with head and neck trauma and characterized by longer latency, rhythmically stereotyped, paroxysmally focal and centrifugal tongue contractions, the pathophysiologic pattern of which has been measured at a frequency of 3 Hz.^e8

Vocalizations

In some disorders, nonvolitional patient-transmitted sounds resemble animal vocalizations. For instance, cri-du-chat syndrome received its name from the characteristic high-pitch cry (strikingly similar to a mewling cat) of the afflicted children. Some of the vocal tics of Tourette syndrome are colloquially referred to as barking tics.6

Unilateral vagal nerve lesions can preclude the normal matched and synchronous opposition of the vocal cords, thereby causing a bovine cough.8 Notwithstanding the unusual nature of the bovine cough, pathoetiologic caution is advised given that the absence of collateral signs of vagal dysfunction may implicate psychogenic underpinnings.^e9

Movement disorders

The widely recognized rabbit syndrome describes a perioral tremor (involuntary, rhythmic, and often vertical mouth movements without tongue involvement) arising from the use of dopamine antagonist therapy (e.g., antipsychotic and certain antiemetic agents).^e10 It may perhaps be better stated as the rabbit sign since a syndrome refers to a collection of signs and symptoms that share a common pathophysiology. This should not be confused with the white rabbit syndrome of orthostatic tremor, a peculiar condition in which patients prefer either sitting down or moving about,8 resulting in almost constant motion reminiscent of the white rabbit in Alice’s Adventures in Wonderland.

Another animal-inspired tremor neurologists are familiar with is the bat-wing tremor: a severely disabling, low-frequency, proximal-dominant upper extremity postural/kinetic tremor that results in an abduction-adduction movement of the arm. It may be seen in cerebellar ataxia, Wilson disease, multiple sclerosis, dystonia, essential tremor, and parkinsonism.^e11

The beasts of neuroradiology and pathology

Basal ganglia

The eye-of-the-tiger sign on brain MRI (pallidal T2 hypointensity with a central zone of hyperintensity) is characteristic of, but not pathognomonic for, pantothenate kinase–associated neurodegeneration, formerly called Hallervorden-Spatz syndrome (an eponym shunned for its Nazi connections). This popular sign has also been reported in multiple system atrophy, corticobasal degeneration, HARP syndrome (hypoprebetalipoproteinemia, acanthosytosis, retinitis pigmentosa, and pallidal degeneration), and progressive supranuclear palsy (PSP).^e12–e16

White matter

The distinct colorations of animal fleeces have also found their way into neurologic descriptions. Neuropathologists (and those preparing for the neurology boards) would be familiar with zebra bodies, broad transversely stacked myelinoid membranes found in the nervous tissue of patients with Fabry disease, metachromatic leukodystrophy, Niemann-Pick disease, GM2 gangliosidoses, and mucopolysaccharidoses.^e17 Some leukodystrophies (metachromatic leukodystrophy, Pelizaeus-Merzbacher disease, and globoid cell leukodystrophy) result in white matter T2 hyperintensity on MRI with occasional hypointense abnormalities within the demyelinated white matter; linear, radiating hypointensities are described as tigroid, while punctate hypointensities take on the appearance of leopard skin (figure 1).^e18–e20

Animal prints

Figure 1. The tigroid pattern (A) in metachromatic leukodystrophy is due to T2-hypointense radial stripes within the hyperintense subcortical white matter, resembling tiger stripes. T2-hypointense (B) or T1-hyperintense (C) spots in the subcortical white matter resemble a leopard's skin. Reproduced from Nandhagopal R, Krishnamoorthy SG. Neurological picture. Tigroid and leopard skin pattern of dysmyelination in metachromatic leucodystrophy. J Neurol Neurosurg Psychiatry 2006;77:344, with permission from BMJ Publishing Group Ltd.

A lesion that involves both frontal lobes and crosses the corpus callosum is commonly referred to as a butterfly lesion, classically suggesting a high-grade glioma or lymphoma, but has also been observed in demyelinating disease, Susac syndrome, and neuronal ceroid lipofuscinosis.^e21–e22

Ventricles and hippocampi

Bat wings have enjoyed a prominent role in radiologic eponyms. Medical students would be familiar with the bat-wing appearance of pulmonary edema on chest radiographs. In Joubert syndrome, dilation of the fourth ventricle has been described as bat-wing shaped.^e23 Additionally, bat-wing dilation of the sylvian fissures on CT or MRI is characteristic of glutaric acidemia type I.^e24–e25

Deep to the sylvian fissure lie the hippocampi, which bear an uncanny resemblance to their Greek namesake, seahorses. With progressive hippocampal atrophy in disorders like Alzheimer disease and frontotemporal dementia, these “seahorses” resemble elephants (hence, elephant sign).^e26

Brainstem and cerebellum

Tegmental mesencephalic atrophy with relative preservation of pontine volume in PSP gives the midbrain the silhouette of a hummingbird on midsagittal MRI (the hummingbird sign).^e27–e28 More ornithologically inclined neurologists have also called it the penguin sign.^e29 Adult-onset Alexander disease (resulting from glial fibrillary acidic protein mutation and pathologically characterized by Rosenthal fibers) demonstrates medullary and cord atrophy with a relatively well-preserved, plump pons; on sagittal MRI, this has been described as tadpole brainstem atrophy^e30 (figure 2).

Tadpole

Figure 2. In Alexander disease, a T2-hypointense periventricular rim (A) may be discernible, but more conspicuously, marked cervicomedullary atrophy with an intact pons contributes to the appearance of the tadpole sign (B) on sagittal MRI sections. Reproduced from Schmidt H, Kretzschmar B, Lingor P, et al. Acute onset of adult Alexander disease. J Neurol Sci 2013;331:152–154, with permission from Elsevier.

Horizontal gaze palsy and progressive scoliosis is a rare genetic disease due to ROBO3 mutation; the dysplastic medulla with its deep ventral sulcus and relative prominence of the inferior olives in comparison to the pyramids has been likened to a butterfly.^e31–e32 (figure 3) Changes in brainstem structures resulting from osmotic demyelination have given rise to various zoologically related radiologic signs including the piglet^e33 and monkey^e34 signs. The unique cerebellar foliation pattern in Lhermitte-Duclos disease results in distinct parallel linear striations called tiger-striping on MRI and CT.^e35

Butterfly

Figure 3. MRI images from 2 patients with familial horizontal gaze palsy and scoliosis (A, B and C, D) compared with a healthy control (E, F), at 2 representative anatomical levels. In both patients, the fourth ventricle is enlarged (A and C) and lacks the normal prominence due to the underlying abducens nuclei (short arrows in E). The butterfly-shaped medulla (B and D) is the result of medullary dysplasia with a prominent deep ventral sulcus (long arrows) and relative prominence of the inferior olives in comparison to the pyramids. Reproduced from Pieh C, Lengvel D, Neff A, et al. Brainstem hypoplasia in familial horizontal gaze palsy and scoliosis. Neurology 2002;59:462–463, with permission from Lippincott Williams & Wilkins/Wolters Kluwers Health.

Vertebrae and spinal cord

The Scotty dog sign refers to the normal appearance of the lumbar spine on oblique radiographs; spondylosis results in a Scotty dog with a “collar” or “broken neck.”^e36–e37 The fish vertebra (or codfish vertebra) sign is characterized by biconcave vertebral bodies occurring as a result of squared-off depression of the vertebral endplates and compression by adjacent intervertebral discs; it is seen in osteoporosis and sickle cell disease^e38 (figure 4).

Fish vertebra

Figure 4. The fish vertebra (or codfish vertebra) sign is the result of exaggeration of the normal concavity of the superior and inferior surfaces of the vertebral bodies. It may be seen in sickle cell disease (where microinfarctions of the central vertebral growth plate result in impaired vertebral growth) or in osteoporosis. Reproduced from Ntagiopoulus PG, Moutzouris DA, Manetas S, et al. The “fish-vertebra” sign. Emerg Med J 2007;24:674–675, with permission from BMJ Publishing Group Ltd.

The bundle of lumbosacral spinal roots originating from the conus medullaris is called the cauda equina, after its resemblance to a horse's tail. MRI T2 hyperintensity of the dorsal columns of the spinal cord in cyanocobalamin-deficiency myelopathy has been called the inverted rabbit ear sign.^e39 Snake eyes or owl's eyes sign refers to the appearance of 2 small, symmetric, T2-hyperintense spots in the spinal cord parenchyma; it is the result of bilateral tract-specific involvement (the affected tracts depend on the underlying pathoetiologic process). Such changes have been reported in compressive myelopathy,^e40 spinal cord infarctions,^e41 amyotrophic lateral sclerosis,^e42 and paraneoplastic myelotractopathy.^e43

Those adorable pandas

The cute pandas have attracted immense public interest and adoration, in addition to their status as an eponym and acronym. Panda eyes are sometimes used interchangeably with raccoon eyes.8 The face of the giant panda sign is a result of midbrain tegmental T2 hyperintensity sparing the red nuclei, in conjunction with normal or low signal intensity of the substantia nigra pars reticulata and superior colliculi hypointensity; it is classically associated with Wilson disease^e44 but has been reported in a case of multiple sclerosis.^e45 The double panda sign is the result of the appearance of the face of the giant panda sign in the midbrain, accompanied by the face of the panda cub or miniature panda sign in the dorsal pons.^e46–e47

The miniature panda face is a result of relative hypointensity of the central tegmental tracts and the medial longitudinal fasciculi, in contrast to the hyperintensity of the most caudal extent of the cerebral aqueduct as it opens into the fourth ventricle. In this circumstance, the apparent panda pattern is bounded inferiorly by the superior medullary velum and laterally by the superior cerebellar peduncles. ^e46–e47

Focal accumulation of galluim-67 citrate in the nasopharynx, parotid glands, and lacrimal glands (the panda sign) when performing gallium scintigraphy is highly characteristic of sarcoidosis.^e48

In its application as an acronym, PANDAS refers to the controversial constellation of syndromic features (an acquired movement disorder, typically tics, in association with behavioral manifestations, classically obsessive-compulsive disorder) derivative of streptococcal infection; Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections.

Animal-inspired eponyms and neurologic practice

Pareidolia, an apophenic phenomenon characterized by misperceptions from random stimuli (e.g., observing faces in the clouds or religious iconography in food), most likely accounts for the ability to recognize a resemblance between clinical phenomena and animal-like attributes.^e49 Despite the negative associations of such illusions (e.g., seeing Jesus Christ on toast), pareidolia may actually be a very useful asset to neurologists.

Pattern recognition and effective communication are indispensable skills to the diagnostic capabilities of any clinician. For neurologists, these skills are particularly important since the intricacies of the nervous system often give rise to recognizable and eloquent syndromes.

For example, the stooped, shuffling, elderly patient with a pill-rolling tremor immediately brings the eponym Parkinson disease to mind. Instead of being lost in complex clinical phenomenology and radiologic descriptions, recognizing a peculiar pattern of abnormalities would direct a neurologist's diagnostic deliberations to a set of differential diagnoses. Further, animal eponyms can be used to succinctly summarize and communicate a complex abnormality without resorting to a litany of awkward, tongue-twisting designations.

CONCLUSION

Identifying and concisely communicating clinical or radiologic patterns of abnormalities is a cardinal component of the practice of neurology. Animal-inspired eponyms should not be dismissed as cabalistic or pejorative but should instead be considered as colorful, useful aides-mémoire that enliven and improve the diagnostic process, facilitate communication, and reinforce understanding of the entity itself, with patently obvious dividends for those we serve.

STUDY FUNDING

No targeted funding reported.

DISCLOSURES

S. Beh received an MS Clinical Fellowship Award from Biogen Idec. T. Frohman has received funding for travel or speaker honoraria from Novartis, Acorda, Genzyme, and Biogen; serves on the editorial board of an NMSS publication; receives publishing royalties from Up-To-Date; serves as a consultant for Acorda, Novartis, and Genzyme; serves on speakers' bureaus for Acorda, Novartis, Genzyme, and Biogen; and receives research support from NMSS and an NIH subcontract grant from UPenn. Her spouse has received funding for travel or speaker honoraria from Teva, Novartis, Acorda, and Genzyme; receives publishing royalties from Up-To-Date; serves as a consultant for Teva, Acorda, Novartis, Abbott, and Genzyme; and serves on speakers' bureaus for Teva, Acorda, and Novartis. E.M. Frohman has received funding for travel or speaker honoraria from Teva, Novartis, Acorda, and Genzyme; receives publishing royalties from Up-To-Date; serves as a consultant for Teva, Acorda, Novartis, Abbott, and Genzyme; and serves on speakers' bureaus for Teva, Acorda, and Novartis. His spouse has received funding for travel or speaker honoraria from Novartis, Acorda, Genzyme, and Biogen; serves on the editorial board of an NMSS publication; receives publishing royalties from Up-To-Date; serves as a consultant for Acorda, Novartis, and Genzyme; serves on speakers' bureaus for Acorda, Novartis, Genzyme, and Biogen; and receives research support from NMSS and an NIH subcontract grant from UPenn. Full disclosure form information provided by the authors is available with the full text of this article at Neurology.org/cp.

Correspondence to: scjbeh@gmail.com

Funding information and disclosures are provided at the end of the article. Full disclosure form information provided by the authors is available with the full text of this article at Neurology.org/cp.