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Downbeat nystagmus
  1. Soumya Sharma1,
  2. Anu Gupta1,
  3. Aviraj Deshmukh1,
  4. Satbir Singh2,
  5. Vinod Puri1
  1. 1Department of Neurology, GIPMER, Jawaharlal Nehru Marg, New Delhi, India
  2. 2Department of Radiodiagnosis, GIPMER, New Delhi, India
  1. Correspondence to Dr Professor Vinod Puri, Department of Neurology, Govind Ballabh Pant Institute of Postgraduate Medical Education and Research (GIPMER), Jawahar Lal Nehru Marg, New Delhi 110002, India; vpuri01{at}gmail.com

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A 22-year-old man presented with progressive weakness and sensory loss in the left arm and leg for 1 year, imbalance while walking for 6 months, oscillopsia, dysphagia and urinary urgency for 3 months. Examination revealed a short neck, low posterior hairline and scoliosis. Downbeat nystagmus (DBN) was appreciated in the primary position of gaze. It increased in amplitude when the patient looked down and out, the so-called Daroff's sign1 (see online supplementary video). He also had lid nystagmus, right partial Horner's syndrome, lower cranial nerve palsies, bipyramidal involvement, ataxia (sensory and cerebellar), and left pansensory loss (up to C3). MRI of the spine revealed a 6 mm descent of the cerebellar tonsils below the foramen magnum (Arnold Chiari malformation type 1; figure 1A (arrow)) with syringomyelia extending from the C2 to D5 vertebral level (figure 1A (arrowhead)). Basilar invagination was noted on CT imaging of the spine, with extension of the odontoid process 10 mm above the Chamberlain line (figure 1B (arrow)).

Figure 1

MRI and CT of the spine. (A) T2-weighted sagittal MRI of the spine reveals a 6 mm descent of the cerebellar tonsils below the foramen magnum (Arnold Chiari malformation type 1 (arrow)) with syringomyelia extending from the C2 to D5 vertebral level (arrowhead). (B) Sagittal CT imaging of the spine reveals basilar invagination: the odontoid process (arrow) extends 10 mm above the Chamberlain line.

DBN is a distinct ocular motor phenomenon that is present in the primary position of gaze. It is characterised by a slow upward drift and a fast corrective downward phase. It is classically and most commonly seen in patients with cerebellar floccular lesions.2 Lesions of the floccular Purkinje cells or flocculovestibular connections activate spontaneous upward drift of the eyes producing DBN. Nearly one-third of patients with this eye sign have an Arnold Chiari malformation.3 Therefore, in the presence of DBN, a thorough investigation for structural lesions at the craniocervical junction should be made, and MRI of the foramen magnum region in the sagittal plane is the investigation of choice.

The treatment includes correction of the underlying cause whenever possible. Base-out prisms can be used successfully if the DBN damps on convergence.4 Studies have suggested that 4-aminopyridine increases the activity in the floccular Purkinje cells, improving fixation.5 Other drugs that may be useful are baclofen and clonazepam.

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Footnotes

  • Contributors SoS and AD collected information and prepared the draft. AG, SaS and VP edited and reviewed the manuscript. All authors reviewed, edited and approved the final version.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.