Diffuse Lower Motor Neuron Disorders

One of the causes of acute quadriparesis or quadriplegia is that of diffuse lower motor neuronal (LMN) dysfunction, resulting in diminished to absent reflexes in all 4 legs. In this instance the immediate differential diagnosis must include acute polyradiculoneuropathy (previously discussed), Coral snake envenomation, tick paralysis, and botulism. Other causes which normally result in normal reflexes with progressive weakness on exercise include polymyositis, myasthenia gravis, and sub-acute organophosphate (OP) intoxication. The nature of these diseases are that they affect some portion of the lower motor unit. Polyradiculoneuropathy affects the myelinated fibers of the motor nerves. Coral snake envenomation, tick paralysis and botulism result from toxins which alter the release of acetylcholine at the neuromuscular junction. Myasthenia gravis and sub-acute OP intoxication alter the release or responsiveness of the neuromuscular junction to acetylcholine on repeated neural activity. Polymyositis directly affects the muscle. The former conditions result in flaccid paralysis, while the latter ones result in weakness, stiffness and collapse on exercise. Coral snakes are limited in their distribution and it should be considered in cases of LMN disease in areas where they are endemic. The ticks which are associated with tick paralysis vary and are present throughout the world. Tick paralysis appears to be seasonal, but can occur at any time. Botulism can occur from food poisoning or from alterations in the intestinal flora. Dogs are fairly resistant to botulinum toxin, but intoxication is occasionally seen.