Type 1 Chiari malformation consists of caudal displacement of the cerebellar tonsils through the foramen magnum. It may also be associated with displacement of the medulla and hydromyelia or syringomyelia. The natural history is variable, with most patients presenting between the 3rd to 5th decades.1 In a reported series of 71 patients, 69% presented with pain, 56% had weakness, 52% had numbness, and 40% complained of unsteadiness.2Mohr et al 1 classified patients' presentations into four main groups: syringomyelia, paraparesis, cerebellar, and “raised pressure'. We describe a patient with a previously relatively asymptomatic complex chiari 1malformation who acutely deteriorated after chiropractic manipulation of the cervical spine.

This white woman first presented at the age of 47 years in August 1995. She had sustained a mild “whiplash” injury in April 1995, having been struck at low speed from behind while sitting in a stationary car. She developed neck pain a few days later and this became progressively more annoying over the next 2 months. She then attended for chiropractic manipulation of the neck. This included repetitive high velocity, low amplitude thrusting movements at the base of the neck. Immediately after the therapy session, her neck pain worsened, spreading to involve the occiput, vertex, and frontal head regions. It was made worse with coughing, lifting, and bending over. She became aware of diplopia and intermittent difficulty swallowing. She had progressive gait instability when walking longer distances. In retrospect, she had many years of poor balance, with difficulty walking on uneven ground when wearing high heels. There was no sphincteric or sensory disturbance. Her history was unremarkable apart from total gastrectomy for a benign peptic ulcer. She was receiving regular B12 injections.

Examination showed normal visual acuity and funduscopic findings. There was bidirectional horizontal gaze evoked nystagmus and mildly impaired horizontal vestibulo-ocular reflex suppression. Vertical pursuit was abnormal with markedly impaired vertical vestibulo-ocular reflex suppression. There was right hypertropia on right gaze. There was no facial weakness or sensory loss. She had a “nasal” quality to her speech, with mild dysrhythmia with rapid consonants. The jaw jerk was pathologically brisk. There was increased tone in the lower limbs. Deep tendon reflexes were increased with positive Hoffman's sign and bilateral extensor plantar responses. She had a wide based gait with moderate truncal ataxia.

Plain radiographs of the neck disclosed assimilation of the posterior arch of C1 into the occiput, and abnormality of the dens. Brain MRI showed prolapse of the cerebellar tonsils through the foramen magnum to the level of the base of C2, with basilar invagination of the peg and angulation of the upper medulla (fig 1). There was mild midline cerebellar abnormality and distortion of the vertebrobasilar system. The aqueduct seemed normal. Laboratory tests disclosed compensated hypothyroidism.

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Figure 1

Preoperative T1 weighted sagittal MRI, showing cerebellar tonsillar invagination and angulation of the upper medulla, and abnormality of the dens and posterior arch of C1.

She continued to deteriorate over the next 12 months, developing vertical nystagmus in the primary position, and became unable to walk unassisted.

In October 1996 she underwent a complex decompression procedure, with anterior removal of the anterior arch of C1, odontoid peg and clivus, and posterior removal of the occipital bone and attached occipitalised arch of C1. The surgery was complicated by development of pneumonia and a loculated empyema requiring a thoracotomy for decortication, and septic arthritis of a C1/C2 zygoapophyseal joint. She required a temporary percutaneous feeding gastrostomy.

Three years after surgery she has very mild residual cerebellar ataxia, eye movement disorder, and mild dysarthria. She is able to eat a normal diet and walks independently.

Various neurological complications have been described with head and neck manipulation. Case reports have most often documented vascular injuries and stroke syndromes.3 4 Cervical manipulation has also been associated with spinal cord injuries and paraparesis,5 phrenic nerve injury,6 and various nerve root disruptions.

The patient reported here represents a case of occult complex Chiari 1 malformation, which acutely decompensated after neck manipulation. The mechanism of injury is probably related to vigorous head rotation with direct traction on the markedly angulated medulla. It is also possible that the anterior compression at the craniocervical junction was worsened by transient subluxation of an already abnormal atlantoaxial joint.

The frequency of complications after spinal manipulation is not known, although the usual public perception is that it is relatively risk free. This patient, and the literature would suggest that there is a real, if small, complication rate with a substantial long term morbidity and disability.

Certain conditions would seem to be absolute contraindications to chiropractic manipulation, and ideally these would be identified before proceeding. Plain radiographs of the spine, with emphasis on the occipitocervical junction, have been suggested as screening tools before manipulation.3 If bony abnormalities or lytic changes are seen, then manipulation should be avoided. Certainly if this rule was followed, the patient would not have shown rapid deterioration. It should be emphasised however, that adult Chiari malformation is not uncommon and may not be associated with gross skeletal abnormalities.

Patients with previous symptoms of brain stem ischaemia should also avoid therapy. Others have also suggested that malignancy, poorly controlled diabetes mellitus, anticoagulant therapy, infection, and hypermobility syndromes are absolute contraindications to spinal manipulation.7 Despite these various precautions, many potentially vulnerable patients will be unidentified and it is likely that patients will continue to present with neurological complications after chiropractic manipulation.