Tetraparesis: Inflammatory diseases

By | September 2, 2013

Chronic inflammatory demyelinating polyneuropathy

Clinical signs: Chronic inflammatory demyelinating polyneuropathy (CIDP) causes slowly progressive LMN tetraparesis in adult dogs and cats with no gender or breed bias (). Signs can relapse intermittently and can progress to tetraplegia. Shifting lameness, a plantigrade stance and ventroflexion of the neck have been described in cats, along with megaoesophagus and regurgitation. Leg tremors and laryngeal and facial paralysis have been noted in dogs.

Pathogenesis: This is an apparently immune-mediated disease in which the inflammatory reaction is focused on peripheral nerve myelin sheathes. The aetiology of the disease is unknown but it appears to be similar to chronic inflammatory demyelinating polyneuropathy in humans.

Diagnosis: Diagnosis is reached by a combination of electrophysiological studies and nerve biopsy. Typically, motor nerve conduction velocity is reduced. There is multifocal paranodal demyelination in teased nerve fibre preparations, and thinly myelinated fibres are visible on semithin sections. Electron microscopy reveals macrophages stripping myelin, and the presence of demyeiinated and remyelinated fibres. There is also a mononuclear infiltrate.

Treatment and prognosis: Treatment consists of immunosuppression with prednisolone (initial dose of 2 mg / kg orally, divided q12h for 1 -2 weeks, followed by gradual tapering over a period of weeks). Most cases respond favourably to this regimen, though some eventually relapse and become steroid resistant.

Ganglioradiculitis

Ganglioradiculitis, also called sensory neuronopathy, ganglionitis and sensory polyganglioradiculoneuritis, is a rare disease in which there is non-suppurative inflammation of the dorsal root and cranial nerve sensory ganglia ().

Clinical signs: Affected dogs are usually mature and may have an apparently sudden onset in signs that are then slowly progressive over a period of months. The signs include ataxia, hypermetria and postural reaction deficits. Spinal reflexes may be reduced, with good preservation of muscle mass and strength due to involvement of the sensory part of the spinal reflexes. Cranial nerve deficits include head tilt, dysphonia and dysphagia, facial hypalgaesia and difficulty in prehension of food. Atrophy of the muscles of mastication may occur and self-mutilation is rarely reported.

Pathogenesis: The aetiology of this disease is unknown but it is speculated to be immune-mediated (). There is one report of a sensory neuronopathy that could have been the result of mercury toxicity (). It has been reported in a variety of different breeds of dog but the Siberian Husky appears to be over-represented.

Diagnosis: Ante-mortem diagnosis is usually presumptive, based on compatible clinical signs and decreased sensory nerve conduction velocity. cerebrospinal fluid findings are usually non-specific, with a mild increase in cellularity and protein levels sometimes reported. As the inflammatory infiltrate is localized to ganglia, nerve biopsy will not establish a specific diagnosis: biopsy of a dorsal root ganglion could be attempted.

Treatment and prognosis: There is currently no effective treatment: immunosuppression does not appear to alter the course of the disease.

Polyradiculoneuritis

Polyradiculoneuritis (inflammation of peripheral nerves and nerve roots) is probably the most common peripheral neuropathy of dogs and cats. It is likened to human Guillain-Barre syndrome.

Clinical signs: Signs typically start in the pelvic limbs and progress over the subsequent 2-4 days to LMN tetraparesis ortetraplegia. Spinal hyperaesthesia has been noted in some dogs.

Pathogenesis: Signs are caused by an inflammatory reaction to axons and myelin sheaths that is most intense atthe level of the ventral nerve root (). Electrophysiological findings in dogs suggest that it is primarily a motor axonopathy (). The disease can be subclassified according to cause as Coonhound paralysis (seen in North America with onset of signs 7-10 days after raccoon bites), idiopathic polyradiculoneuritis and post-vaccination polyradiculoneuritis (extremely rare). An important association in human patients is concurrent infection with a specific serotype of Campylobacter jejuni () but no similar relationship has been established in domestic pets to date.

Diagnosis: The number of diseases that cause acute onset of LMN tetraparesis or tetraplegia is limited and polyradiculoneuritis should always be suspected when this clinical picture occurs. Other diseases to consider include botulism and, in the USA and Australia, tick paralysis. Electromyography reveals spontaneous electrical activity consistent with denervation (fibrillation potentials and positive sharp waves); nerve conduction velocities are dispersed and reduced, with nerve roots more severely affected than distal nerve (). Definitive diagnosis is established by nerve biopsy ().

Treatment and prognosis: Treatment centres on supportive care and rehabilitation. Corticosteroid administration is not beneficial. Humans are treated by plasmapheresis and intravenous immunoglobulins but there are no reports of this in dogs or cats. The pulmonary function of recumbent animals must be monitored closely. If hypoventilation is suspected, an arterial blood gas analysis should be performed to determine whether mechanical ventilation is necessary. Animals should be turned and passive range-of-motion exercises and massage of limbs should be performed at least four times a day. If pulmonary function is unaffected, with adequate supportive care most animals will recover over a period of 3-6 weeks. The need for mechanical ventilation, the presence of aspiration pneumonia and severe muscle atrophy with development of contractures all worsen the outcome.

Protozoal neuritis

Clinical signs: Clinical signs can be extremely variable as a result of infection of muscle, peripheral nerve and the CNS. Typically the pelvic limbs are affected first and the combination of myositis and neuritis causes rigid extension of the limbs, with severe muscle atrophy and contractures developing quickly (). However, multifocal CNS signs can be present and can be the predominant sign ().

Pathogenesis: Infection with the protozoal organisms Toxoplasma gondii and Neospora caninum can cause an intense polyradiculoneuritis in dogs, accompanied by a myositis (). Clinically significant protozoal infections affectyoungorimmunocompromised dogs. Dogs are both definitive and intermediate hosts for N. caninum, with cattle, sheep, goats and other mammals also acting as intermediate hosts. Cats are the definitive host for T. gondii, with most mammals serving as intermediate hosts. Infection can occur transplacentally (common for N. caninum), by ingestion of protozoal cysts from infected secondary hosts, and by ingestion of oocysts shed in faeces (common for T. gondii). N. caninum is probably the most common protozoal infection in dogs, particularly as retrospective immunohistochemical evaluation of archived tissue confirms that many animals previously diagnosed with toxoplasmosis were actually infected with N. caninum.

Diagnosis: Definitive diagnosis can be made by identification of the organisms by muscle () or nerve biopsies, combined with serology. Serology alone can be confusing, with a high rate of false positive titres, particularly in the case of toxoplasmosis. Polymerase chain reaction (PCR) analysis of cerebrospinal fluid may provide a more specific diagnosis in the future.

Treatment and prognosis: Treatment of protozoal infections can be attempted, using clindamycin but a combination of trimethoprim / sulphonamide and pyrimethamine may be more effective in actually killing the organisms and penetrates the CNS well. Animals on this protocol can be supplemented with folic acid, and azithromycin can be added as it is effective in killing intracellular organisms. Prognosis depends on the severity of clinical signs and muscle contractures. Recovery of normal function is unlikely but institution of treatment can prevent progression of signs. The prognosis is better if treatment is initiated while signs are still mild, but relapses can occur.

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