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• Authors response to Dr Hughes' comments
  Aisling S Carr
  Published on: 28 June 2017
• Correspondence and referee’s reports on Carr AS, et al. Wisdom tooth extraction causing lingual nerve and styloglossus muscle damage. Pract Neurol 2017;17:218–221.
  Tom Hughes
  Published on: 26 June 2017

• Published on: 28 June 2017

  Authors response to Dr Hughes' comments

  • Aisling S Carr, Consultant Neurologist MRC centre for neuromuscular diseases, National Hospital for Neurology and Neurosurgery

  We thank Dr Hughes for his thoughtful letter and his previous extensive comments as part of the reviewing process.

  The main issue Dr Hughes has raised is the possibility of another local structural lesion. He asks that “Some cross checking with digital examination of the floor of the mouth, palpation of the tongue, or the results of attempts by a clinician to correct the position of the tongue may be all that is required to confirm or refute the working diagnosis.

  We had already addressed this in our paper “The ENT and oral maxillofacial surgeons had noted a small post-traumatic neuroma/granuloma at the left retromolar space but with no other oral structural abnormality “. And expanded on this in response to the query in Dr Hughes’s first review, “No structural lesion to the tongue muscle or its attachments was observed on clinical examination by an experienced ENT surgeon or on independent examination by an oral maxillofacial surgeon”.

  We feel our explanation as outlined in our paper remains the most plausible.

  Conflict of Interest:
  None declared.

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• Published on: 26 June 2017

  Correspondence and referee’s reports on Carr AS, et al. Wisdom tooth extraction causing lingual nerve and styloglossus muscle damage. Pract Neurol 2017;17:218–221.

  • Tom Hughes, Dr University Hospital Wales

  Dear Editors,
  Carr AS, et al. Pract Neurol 2017;17:218–221. doi:10.1136/practneurol-2016-001491
  In the interests of enhancing our understanding of bulbar function from the perspective of the jobbing clinical neurologist, I am writing to you regarding a publication in this month’s edition of Practical Neurology (Carling et al.). As it stands I do not think the case report does justice to the scholarship of the seven authors.
  I enjoyed formally refereeing the paper on two separate occasions (enclosed), and offered a third comment (“I think the patient has a lingual nerve palsy and a tethered tongue on the left, both occurring as a complication of surgery”) by email, in the hope that it could appear in a little box as “reviewer’s comments”. I now think that I would have provided a better service to PN if I had sent this single sentence to you instead of the first review.
  In the report, the authors champion the careful approach required in patients with very focal abnormalities involving the lower cranial nerves and the muscles they innervate. They describe in pictures and very useful tables—copies of which are already on my office wall—the detailed knowledge that is required to avoid misattribution in the crowded and inaccessible house of the structures involved in bulbar function.
  The patient concerned had a third molar removed and postoperatively had a lingual nerve palsy. This complication is anticipated, and is included in the consent pro...

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  Dear Editors,
  Carr AS, et al. Pract Neurol 2017;17:218–221. doi:10.1136/practneurol-2016-001491
  In the interests of enhancing our understanding of bulbar function from the perspective of the jobbing clinical neurologist, I am writing to you regarding a publication in this month’s edition of Practical Neurology (Carling et al.). As it stands I do not think the case report does justice to the scholarship of the seven authors.
  I enjoyed formally refereeing the paper on two separate occasions (enclosed), and offered a third comment (“I think the patient has a lingual nerve palsy and a tethered tongue on the left, both occurring as a complication of surgery”) by email, in the hope that it could appear in a little box as “reviewer’s comments”. I now think that I would have provided a better service to PN if I had sent this single sentence to you instead of the first review.
  In the report, the authors champion the careful approach required in patients with very focal abnormalities involving the lower cranial nerves and the muscles they innervate. They describe in pictures and very useful tables—copies of which are already on my office wall—the detailed knowledge that is required to avoid misattribution in the crowded and inaccessible house of the structures involved in bulbar function.
  The patient concerned had a third molar removed and postoperatively had a lingual nerve palsy. This complication is anticipated, and is included in the consent process. This part of the report is a valuable reminder for PN readers, but I suspect it rarely reaches neurologists as dentists and oral surgeons are so familiar with the clinical features, and the medicolegal implications.
  The unusual postoperative complication in the patient described is the position of the tongue. The tongue is tilted to the left side regardless of the movements attempted, with predictable effects on relevant phoneme production and on swallowing. There has been no recovery after four years. The abnormality is striking, particularly as in complete twelfth nerve palsies—where many of the muscles of one side of the tongue can be shown to be involved clinically—electrically and radiologically the tongue is not fixed in the way described, and patients seem able to compensate relatively well with the passage of time.
  The first edition of the paper attributed this to a loss of proprioception in half of the tongue, due to a loss of fibres conveying muscle stretch sense from the tongue. I questioned this in the first review, and in the second version the position of the tongue was attributed to dysfunction of styloglossus, an elevator of the tongue that fans out to insert along its lateral border. I questioned this in the second review suggesting that a more likely explanation was tethering of the tongue; the patient describes their tongue as feeling stuck, and subsequently it was suspected that there was granulomatous tissue at the site of the operation.
  The authors’ point about the need for accurate diagnoses of impairments in this clinical territory is well made. This is clearly relevant in accurately identifying and naming the muscles and cranial nerve branches involved but also to distinguish pure neurological disease from temporally and anatomically adjacent structural disease. In the limbs this is more straightforward because the repertoire of signs is so broad. Observation at rest and during movement, and the testing of tone, strength, reflexes, coordination, sensation, and function is relatively straightforward, as is a basic musculoskeletal examination to look for scar tissue, contractures and joint deformities. Attempts to carry out similar tests for the jaw, larynx, pharynx and tongue are unhinged by their size and structure and the limited views, access and purchase. This congestion cramps the traditional style and sequence of neurological examination at the bedside and may leave the examiner inferring the presence of deficits on the grounds of limited evidence. In the limbs, suspected abnormalities of tone can be triangulated with strength and reflexes, and suspected weakness with inspection and passive range of movement. The signs accepted by one examiner can easily be verified or refuted by others and even quantified using validated rating scales. For the lower cranial nerves, such cross checking and shared scrutiny is more difficult. This may explain a tendency to over interpret the information that is retrieved or inferred; for the tenth nerve the gag reflex has been used in the past to inform risk assessments related to conscious level, swallowing and even mountain sickness.
  With these considerations in mind, I am concerned that there may be another explanation for the findings that would further inform the approach to such cases and illustrate even more vividly the need for a special approach in cases of very localised bulbar dysfunction. Some cross checking with digital examination of the floor of the mouth, palpation of the tongue, or the results of attempts by a clinician to correct the position of the tongue may be all that is required to confirm or refute the working diagnosis.
  I raise these concerns in the interests of maintaining the high standards, for authors and reviewers, of Practical Neurology.

  Yours sincerely,

  TOM HUGHES
  Tom.Hughes2@wales.nhs.uk

  Reviewer comments to editors (first draft)
  Thanks very much for asking me to review this paper. It is a single-case report about loss of proprioception in the tongue with lingual nerve dysfunction, a common but usually transient complication of third molar removal (related to either the anaesthesia or surgery or both). There are stretch receptors in the tongue, but traditionally it has been thought that their afferent neurones travel with the hypoglossal rather than the lingual nerve.
  At first I thought it was identifying something important about the tongue and in particular its proprioception, but with repeated reading I have become less certain about the interpretation of the clinical signs, and the conclusions drawn.
  Immediately following third molar removal under local anaesthetic the patient described had persistent dysarthria in association with sensory loss in a lingual nerve distribution, with what are described as pseudoathetoid movements of the tongue.
  I think it is a scholarly article and I hope the authors will tolerate my questions!
  Was the surgery for the removal of the left third molar unusual in any way, and in particular were any incisions required in to the gum of the third molar, and if so were they made on the buccal (standard practice) or lingual side? This would inform thinking about the possibility of additional complications.
  Were tests done to demonstrate loss of proprioception in the tongue? I think this is important given their use of the term pseudoathetoid in the title of the paper.
  Options include holding the tongue gently with small padded forceps and with the patient’s eyes closed testing awareness of passive tongue movements. As with other tests of lower cranial nerve dysfunction the field of view in such a crowded area is not great and the repertoire of signs limited, but if the described tongue movements are a result of proprioceptive loss, I would expect some detectable impairment of awareness of tongue position. This is of particular relevance as in day-to-day function any sensory loss in and on the tongue was apparently uncompensated for by the completely normal right side sensation (lingual and buccal) and the normal left sided sensation of the buccal mucosa, teeth, hard palate and other closely tongue-apposing structures.
  Is it reasonable to compare and contrast this patient’s bizarre tongue movements with other patients who have more extensive intraoral sensory loss e.g. lateral medullary syndrome, pontine plaques and cavernomas etc.? I think we see dysarthrias commonly, and tongue deviation secondary to motor problems, but not bizarre tongue movements that we attribute to sensory loss. With such a high density of receptors in the tongue and mouth, and the relatively small area of sensory loss on just one side of her tongue and gum, it seems improbable that she would not be able to overcome a unilateral sensory problems, and relearn normal speech and swallowing.
  Is there another reason why she has ended up so disabled by a unilateral sensory problem? Could it be structural or motor?
  The patient describes feeling as though the tongue is stuck, something that suggests a degree of preserved proprioception, but also could suggest a structural problem. I would be interested to know if the floor of the mouth and base of tongue was palpated, digitally, on the left side to detect any persistent post operative changes, particularly any involving tongue muscles, as some of the movements of the tongue could be explained by a motor problem. I note that there was no wasting or fasciculation of the tongue and that an EMG was normal but the extrinsic muscles of the tongue may still be dysfunctional, and I would like to ask about two.
  I note that the tongue at rest had a tendency to point to the right (rather than be randomly positioned in the mouth as would be expected with significant proprioceptive loss), and in figure 1 the right side seems higher than on the left. I would be interested to know if this pattern of movement could be explained by an absence of styloglossus function on the left. This muscle pulls the tongue backwards and upwards. A loss of function may explain the resting position of the tongue and the tendency of it to point to the right, as the push-me-out, pull-me-back interaction of genioglossus and styloglossus would be lost on the left, and the push-me-out action of left genioglossus would be unopposed, resulting in a tendency of the tongue to point to the right.
  The hyoglossus muscle pulls the tongue down and theoretically if it was damaged or changed by surgery it could be tethering the tongue on the left, effectively pulling it down and creating the consistently asymmetrical position in the mouth.
  Is there any chance that surgery could have damaged these muscles or their nerve supply?
  Regarding the possibility of a motor problem they give very little information about her speech. I would be interested to know whether she was able to reliably produce alveolar and velar plosives, and whether lingual fricatives were normal. There is also no information about the nature of her swallowing problem, particularly whether there was anything to suggest, clinically or on a videofluoroscopy, inadequate apposition of the base of the tongue with the posterior pharyngeal wall.
  The sequence of activation of the muscles involved in swallowing is immutable, and can be initiated voluntarily, and is not in anyway dependent on lingual nerve function therefore it is difficult to attribute her swallowing problem to sensory loss of any kind in the anterior tongue. This is another reason I would be interested to know if a motor or structural problem could underlie her symptoms, unchanged after four years.
  Overall I feel that not enough evidence has been gathered to justify attributing the tongue movements to a problem with proprioception, but I would be intrigued to review more information about the clinical findings.
  There are some minor points of accuracy relating to the motor innervation of palatal elevation (X and V, not IX), the relevance of inferring that a present gag reflex in a conscious adult tells us anything about swallowing function (analogous to saying that someone can walk because they have knee and ankle reflexes), or that an absent palatal or pharyngeal reflex necessarily means that there is sensory loss (in lots of normal adults palatal and pharyngeal movement is not elicited by their stimulation). There is one typo (dysphasia instead of dysphagia) and in the abstract a mistake (facial nerve instead of lingual nerve).
  I have enjoyed reviewing the paper and would be interested to see a second draft.
  Reviewer comments to editors (second draft)

  Thank you very much for asking me to review this paper. I saw an earlier version in which a loss of proprioception/muscle stretch sense in the tongue (as a feature of a lingual nerve palsy) was thought to be contributing to the clinical picture. In this revised version it is suggested that in addition to the lingual nerve palsy there is selective involvement of styloglossus, and that this explains the abnormality of tongue movement.
  I have read and reread the paper and have once again enjoyed checking and cross checking the neuroanatomy. I really enjoyed the scholarship of the authors involved in describing each individual intrinsic and extrinsic muscle of the tongue and suggesting ways in which clinicians can examine their function and I think this version is an improvement on the first.
  However I still have some reservations about the central message of the report –in particular the selective involvement of styloglossus - and I feel sure that the authors would want me to challenge their conclusions.

  A lingual nerve injury is very well described as a complication of third molar removal and this was clearly the case in this patient. I will not comment further on the clinical features that are clearly a result of a lingual nerve palsy.
  What is less clear is the mechanism underlying the position of the tongue at rest, and during phoneme production.
  The most striking, and possibly most relevant, clinical sign in this case is the depressed position, at rest, of the posterolateral aspect of the tongue. This does not correct when the subject sees her tongue in the mirror, and appears to have remained fairly static despite therapy and the passage of time (four years).
  This is attributed to the selective involvement of the styloglossus muscle which (Gray’s Anatomy) “ is the shortest and smallest of the three styloid muscles and passing downwards and forwards divides into two portions, one longitudinal which enters the side of the tongue near its dorsal surface, blending with the fibres of the Longitudinalis linguae inferior in front of the Hyoglossus, and the other, oblique portion, overlaps the Hyoglossus and decussates with its fibres”.
  Changes in speech production are also attributed to a problem with styloglossus (which retracts and elevates the tongue) in particular difficulty with lingual fricatives, as are changes in swallowing.
  Other features of note are that before the patient attended the peripheral nerve clinic ENT surgeons had commented on a post-traumatic neuroma/granuloma at the left retromolar space and I note the patient’s comment about “a sticking of her tongue” when speaking and the pain she reported a month later around the operative area.

  Conclusion
  I find it difficult to believe that dysfunction of styloglossus is responsible for the problems with tongue movement in this patient for a number of reasons:
  1 By the time the muscle has reached the angle of the jaw it is starting to fan out and it seems unlikely that the whole muscle could be transected during dental surgery without the surgeon noticing
  2 It is a small muscle
  3 MR imaging does not reveal atrophy of the tongue or any selective atrophy of styloglossus (or any other tongue muscle) and yet the disability is severe (she lost her job in telesales) and her speech did not improve with therapy or the passage of time.
  4 I have not seen persistent changes in the posture of the tongue, at rest, in complete unilateral hypoglossal nerve palsies when all muscles lose their opposite number, and all of the muscular push-me-pull-you is unopposed, and unapposed.
  5 For the position of the tongue to be explained by the loss of styloglossus we would have to accept that at rest the muscle is in fact contracting and elevating the base of the tongue.

  My lingering concern is that the left tongue base is tethered in to the floor of the mouth posterolaterally.
  Therefore I would be very interested to know if palpation of the tongue and floor of the mouth is normal and in particular if the left dorsolateral tongue can be elevated by the examiners finger or fingers in the same way as it can on the right side.
  If this is the case then the report would be very valuable as it would highlight the importance of excluding structural disease before attributing changes in bulbar function to purely neurological deficits.

  I hope this is helpful and I look forward to further correspondence.
  Tom

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  Conflict of Interest:
  None declared.

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