Abstract

A 14-year-old male Komodo dragon developed neurologic deficits after a brief incident of hyperthermia at Chester Zoo. Initial neurologic assessment revealed generalized poor muscle tone. The animal was unable to bear weight effectively on the right front limb and was also unable to hold its cervical spine in sufficient extension to facilitate normal walking. Poor abdominal tone was hindering locomotion and general movement, exacerbated by poor exercise tolerance and attention span. There was increased rigidity and thus, limited movement through the cervical and thoracic spine.

A neurologic assessment chart was developed to monitor progress objectively. This chart was clinical-sign centric in that we started with several behaviors we expected the animal to be able to accomplish and highlighted methods to test these.

The requirements for the Komodo dragon, as minimum outcomes from a series of physiotherapy sessions, were:

• To be able to walk unaided for more than five steps (and thus thermoregulate).
• To show unaided prehension of food.
• To show interest in the females (and thus fulfill one of his main conservation purposes as a breeding animal).

The physiotherapy sessions included leg, neck, and tail coordination and weightbearing exercises (developed by Equine and Canine Solutions [physiotherapists], Hartford, Northwich, Cheshire, UK). A daily swimming routine was incorporated to help with coordination and to achieve extra focal stimuli. A large indoor pool in the enclosure was used for this hydrotherapy.

After one month improvements seen when compared to the initial presentation included:

• Increased exercise tolerance (from 10 to 30 minutes).
• Initiated walking, especially away from unpleasant stimuli.
• Each limb would move independently during locomotion.
• Range of movement of cervical and thoracic spine improved with external mobilization using a specifically designed neck brace.
• Abdominal muscle tone improved.
• Attention span improved—possibly due to changing stimuli and/or surroundings.
• Strength improving, especially against resistance.

However, after five months of physiotherapy treatment muscle wastage became obvious over several weeks. There was consensus between the reptile keepers, curators, vet team, and physiotherapists that physiotherapy had reached a plateau of improvement with locomotion ability beginning to regress, associated with the obvious muscle wastage and weight loss.

The physiotherapists felt there was little chance of significant improvement and that they had exhausted therapy options. In view of this and that, despite intensive therapy, he hasn’t fulfilled the original criteria a decision was reached to euthanatize him on welfare grounds (IV saturated potassium chloride [KCl] solution under general anesthetic). This was used rather than pentobarbitone to protect neurologic ultrastructure.

On gross postmortem there was marked muscle wastage over tail and limbs, despite having excellent coelomic fat stores. This could indicate a neuromuscular deficit or disuse atrophy. There were minimal changes elsewhere. Cranial MRI did not highlight any changes; however, histopathology indicated vacuolation and spongiosis of the tectum. The tectum refers to the dorsal portion of the midbrain. The midbrain processes information from the senses and controls how the animal orients itself towards them, such as turning towards a sound. Thus, the tectum is vital in allowing the animal to recognize patterns in its environment via direct auditory and visual input. Damage to this area of the brain can at least partially explain the Komodo dragon’s observed clinical signs. In mammals at least, the anterior part of the midbrain also incorporates the cerebral peduncle, which is a large bundle of axons travelling from the cerebral cortex through the brain stem and these fibres are important for voluntary motor function.² The peduncle communicates with the tectum to allow special orientation towards or away from a stimulus. The peduncle appears both part of the pyramidal and extrapyramidal tracts, although opinion is divided on this. Birds and reptiles predominantly utilise the extrapyramidal system for motor control.

This case highlights an environmental issue that, while rectified speedily, still produced severe neurologic damage. A paucity of information is available on clinical neurology in reptiles.^1,3,4 This type of neurologic condition had not been recorded in Komodo dragons before.²

As far as the authors are aware, the methods of physiotherapy employed in this case have never been employed in a large lizard before. Although we saw good initial improvement, especially when increasing the positive stimulation from the environment, the damage to the tectum discovered on histopathology precluded a favorable outcome. Unlike mammalian brains, lizard brains appear to retain significant ability for neurogenesis including regeneration of injured neurons, particularly in the forebrain,⁵ but the lesions were too severe in this case.

Literature Cited

1.  Bennett RA, Mehler SJ. Neurology. In: Mader DA, ed. Reptile Medicine and Surgery. 2nd ed. St. Louis, MO: Saunders Elsevier; 2006:239–250.

2.  European Taxon Advisory Group Advisor. Personal Comm. 2006.

3.  Keeble E. Neurology. In: Girling SJ, Raiti P, eds. BSAVA Manual of Reptiles. 2nd ed. Br Small An Vet Assoc. Quedgeley, Gloucester, UK. 2004:273–288.

4.  Wyneken J, Mader DR. Reptilian neurology: anatomy, function, and clinical applications. AAZV Conference workshop notes. 2006.

5.  Olmstead D. Functional architecture of the brain. 2004. www.neurocomputing.org. (VIN editor: link was not accessible as of 1/15/2021.)