Progressive Gait And Limb Ataxia Case Study Biology Essay

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As motor and sensory functions in the normal body are mutually - dependent, I would conclude that Mr X is suffering from marked progressive sensory ataxia as a result of the peripheral neuropathy. The key examination findings of impaired proprioception and vibratory sense as well as the absence of vertigo, nystagmus and dysarthria all correlate with this. Limb ataxia was also present, although limited to the lower extremities, and Mr X had absent ankle reflexes and a positive Rhomberg's test, all of which are findings in sensory ataxia.

The cell bodies of motor neurons are found in the ventral horns of the spinal cord and from here motor neurons travel to the neuromuscular junctions at the muscle they innervate. Primary sensory neurons have cell bodies that lie in the dorsal root ganglia, outside the spinal cord, and travel peripherally to specialised sensory end receptors (i.e. thermoreceptors, mechanoreceptors and nociceptors).

Preganglionic sympathetic autonomic fibres originate in the intermediolateral column of the spinal cord and then synapse in the ganglia of the sympathetic trunk. Conversely, preganglionic parasympathetic fibres extend from their cell bodies (in the brainstem or sacral spinal cord) to terminal ganglia near the organs that they innervate.

The dorsal root ganglia emit central projections that enter the spinal cord via the dorsal roots. The ventral roots carry motor axons while the dorsal roots carry sensory axons; within each spinal segment the two combine to form mixed sensorimotor nerves. These mixed nerves then form plexuses in the cervical, brachial and lumbosacral regions, and the major anatomically defined limb nerves arise from these plexuses.

Mixed nerves are made up of large amounts of myelinated and non - myelinated nerve fibres of differing diameters organised into bundles. Motor neurons and large fibre sensory nerves that mediate position and vibration sense are large myelinated nerve fibres, while small unmyelinated and thinly myelinated nerve fibres are responsible for light touch, pain, temperature and autonomic information.

Most peripheral nerves carry incoming sensory information (afferent fibres) and outgoing motor and autonomic messages (efferent fibres), and it is important to note that the motor and sensory functions of the body are interdependent.

Each bundle of nerve fibres is surrounded by the perineurium, which is made up of layers of specialised cells separated by layers of collagen. Several bundles are bound together by the epineurium (fibroadipose tissue made up of arteries, veins, and lymphatics), a nerve bundle's interstitial connective tissue. Myelinated nerve fibres have junctions between adjacent Schwann cells called 'nodes of Ranvier' which are responsible for the conduction of nerve impulses.

Various injurious processes (including infection, medication toxicity, vascular inflammation, endocrinopathy, vitamin deficiency, mechanical injury and genetic influences) can potentially cause injury to the peripheral nerves, mainly via disruption of the blood - nerve barrier and increased vascular permeability. As a result, vasoactive substances are able to enter, complement activation occurs, and inflammatory intermediates (cytokines, interleukins and tumour necrosis factor) are secreted. This results in oedema, inflammation, ischemia, and eventually, infarction of nerve fibres.

Axonal degeneration results when the axon or cell body is the main site of injury. Demyelination and remyelination occur as a response to many inflammatory and immunologic conditions causing loss of myelin along the myelinated axon.

Processes that affect small fibres produce sensory changes and pain. Symptoms may include reduced sensitivity to stimuli or burning and tingling sensations. Pain and temperature sensation may also be impaired and autonomic dysfunction may be present.

In most forms of peripheral neuropathy the biggest and longest nerve fibres are affected, so sensory loss is most severe over the feet and legs, and, if the upper limbs are affected, over the hands. Sensory loss often occurs in a glove and stocking distribution, but it is important to remember that loss of sensation is gradual and spreading from the distal to proximal regions (i.e. from the toes  feet  legs as the disease progresses). The face, thorax and abdomen usually retain full sensation, except in the most severe cases.

Demyelinating neuropathies tend to cause paraesthesia early in the course of the disease. It occurs in the distal regions of nerves, so when short nerves are involved, the paraesthesia occurs in proximal body parts.

Sensory loss in peripheral neuropathy generally affects all areas of sensation - pain, touch, temperature, vibration, and proprioception - to varying degrees. Certain diseases of peripheral nerves selectively damage different sized nerve fibres, so, for example, degeneration or demyelination of large nerve fibres will cause a loss of proprioception and vibratory sense, whilst pain, temperature and light touch perception will be relatively preserved.

Severe peripheral neuropathy can cause repeated, involuntary writhing movements in outstretched fingers and toes. Sensory ataxia results when the large diameter nerves travelling to the spinocerebellar tracts are affected.

Involvement of the small myelinated and unmyelinated nerve fibres causes dysfunction in pain, temperature and autonomic sensation, whilst proprioception, vibration and tactile sense are retained.

Diminished deep tendon reflexes are one of the earliest signs of motor dysfunction, but motor symptoms can range from mild weakness to complete paralysis. Stumbling, clumsiness, and weakness are common because of the effects on the intrinsic muscles. Denervation of muscles eventually leads to muscle atrophy, so in long - standing peripheral neuropathy hands and feet take on a skeletal appearance.

Autonomic changes are especially common in peripheral neuropathy secondary to diabetes; the skin becomes smooth, cold and shiny, and is usually dry and lacking in perspiration. Neuropathy secondary to systemic disease often results in orthostatic hypotension.

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