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Case Report: Distal denervating disease in an eight-year-old Labrador Retriever

An eight-year-old male, neutered Labrador Retriever was referred for assessment of paraparesis. Two days prior he had appeared ataxic behind. The following day he was having difficulty standing, and collapsed after a short distance. The owners reported that he was vocalising, especially at night, but attributed this to frustration at his disability rather than a pain response.

Examination

A general physical examination revealed no abnormal findings. His condition-score was good. He was able to walk a few strides if helped to his feet, but collapsed to sternal recumbency. Neurologic examination revealed normal mental status and normal cranial nerve function. There were conscious proprioceptive deficits in all four limbs, but most marked in the pelvic limbs. Muscle tone was normal in all limbs. Segmental spinal reflexes were also found to be normal. No focus of spinal pain could be identified. Conscious pain perception was present in all four limbs.

Repeat examinations were performed to ascertain whether the condition was progressive. Later the same day the paresis had progressed to tetraplegia. Segmental reflexes were again considered normal, but muscle tone in all four limbs was reduced. 12 hours later muscle tone was further reduced, and appendicular spinal reflexes were lost the day after that.

Differential diagnosis

The most likely would be an idiopathic, peripheral neuropathy, although atypical neuromuscular disorders or myopathies were considered. Inflammatory, toxic and metabolic causes also needed to be ruled out.

Investigations

Routine haematology and biochemistry was found to be within normal limits. Serology for Neospora was negative, whereas IgG levels for Toxoplasma were supportive of previous or possible active exposure.

Survey chest radiography failed to identify occult megaoesophagus, and an edrophonium response test was negative, making atypical myasthenia gravis unlikely.

On the basis of the above findings, a provisional diagnosis of distal denervating disease (DDD) was made. However, atypical protozoal polyradiculoneuropathy could not be ruled out.

Treatment

A 30-day course of clindamycin (Antirobe, Pharmacia) 450mg q12h P.O., was given. Supportive treatment, including regularly turning, deep bedding, massage, passive and active physical therapy, pulsed magnetic field therapy, neuromuscular electrical stimulation, enemas, urinary bladder catheterisation, NSAID therapy for joint stiffness and hyperaesthesia, and sedation for anxiety were all employed at various times until nerve function spontaneously recovered. An episode of bacterial cystitis resolved with a short course of antibiotic.

Outcome

Appendicular spinal reflexes returned two weeks after presentation. Despite intensive physical therapy, neurogenic atrophy of the limbs resulted in marked muscle loss. Three weeks after presentation hydrotherapy was started as soon as voluntary movement was noted in the limbs. The following week the dog was able to rise to sternal recumbency, and the dysuria resolved. By eleven weeks, nerve function had recovered sufficiently to allow standing briefly, and then walking a week later.

Discussion

DDD is the commonest, acquired polyneuropathy seen in the UK. There is no sex, age or breed predilection. Although not often seen in general practice, it should be included as a differential in any case presenting with tetraparesis. The cause is unknown, but may be similar to related conditions, including Coonhound paralysis seen in North America (thought to be a delayed hypersensitivity response to racoon saliva seen in dogs bitten 10-14 days previously) and Guillame-Barre syndrome in children. Both these conditions also present as a distal denervating disease with motor and proprioceptive losses. In all three, the prognosis is excellent with appropriate care. Recovery is spontaneous, and there is no effective specific treatment for the condition. Dedicated nursing will result in a successful outcome in virtually all cases. Relapses are unknown, and fatalities are rare. However, in some, the neuropathy may progress to involve the intercostals nerves, necessitating prolonged ventilatory support.

A diagnosis of polyneuropathy can often be made on the history and clinical findings alone. Further investigation of the neuromuscular systems may also comprise CSF analysis, nerve conduction velocity testing, and electromyography. Peripheral nerve/ muscle biopsy may also provide useful information.

This case was unusual in that in the author’s experience, the majority of cases are ambulatory within three to six weeks of the onset of signs. Here, despite a favourable temperament, it took nearly three months for nerve function to recover sufficiently to enable walking again.