Nervous disorders

Chapter 9 Nervous disorders




Introduction


The diseases and disorders covered in this chapter have predominantly nervous signs. Consequently, a wide etiological range is covered including nutritional conditions (e.g., cerebrocortical necrosis), metabolic disorders (e.g., hypomagnesemia), bacterial and viral infections (e.g., listeriosis and rabies), parasites (e.g., Coenurus cerebralis), physical and traumatic incidents (lightning strike and electrocution), and miscellaneous conditions of uncertain etiology (e.g., bovine spongiform encephalopathy). However, other diseases with significant clinical nervous signs may be featured elsewhere and include tetanus (12.66–12.68), botulism (12.69), and lead poisoning (13.29).


Nervous conditions may be difficult to appreciate in “still” photographs, since their clinical assessment is based on changes in behavior, movement, gait, and stance. An understanding of the normal animal is therefore extremely important. Where problems of recognition occur, the text has been expanded in an attempt to describe those changes that cannot be photographed.



Cerebrocortical necrosis (polioencephalomalacia)




Clinical features


CCN is seen most commonly in calves that are 2–6 months old, often following a dietary change when on high-concentrate rations. The Simmental crossbred calf in 9.1 has a characteristic “star-gazing” stance. Signs can be very variable depending on whether the onset is acute or subacute. Other signs include depression, ataxia, head-pressing (9.2), and cortical blindness. Autopsy lesions (9.3) are normally symmetrical and occur in the frontal, occipital, and parietal lobes. Congestion and yellow degeneration of the cortical gray matter (A) is seen, typically at the junction of the white and gray matter, particularly on the left and right extremities. Affected brains will fluoresce blue-green under ultraviolet light.








Metabolic diseases


Metabolic diseases are included in this chapter, since many of their presenting clinical signs are behavioral or nervous. Typically, such signs occur when homeostasis has been extended beyond physiological limits. Four conditions are illustrated: hypomagnesemia, hypocalcemia, acetonemia or ketosis, and fatty liver syndrome.



Hypomagnesemia (“grass staggers”, “grass tetany”)




Clinical features


the Friesian cow in 9.4 fell and developed extensor spasm when being brought in for milking. Note the “staring” eye, dilated pupil, frothing at the mouth, and sweaty coat. In 9.5 the crossbred cow from Queensland, Australia, shows similar eye changes. The head and the hind legs are in extensor spasm. Violent paddling movements of the forelegs and head have resulted in loss of foliage, exposing the bare earth. Less severely affected cows may walk stiffly, are hypersensitive to touch and sound, and urinate often. Precipitated by stress and seen especially in temperate climates, the condition is induced by grazing magnesium-deficient or high-potassium pastures, and other pastures where magnesium uptake is poor. Concurrent hypocalcemia may be an exacerbating factor.





Differential diagnosis


hypocalcemia (9.6, 9.7), BSE (9.369.38) encephalitis, listeriosis (9.11, 9.12), ketosis (9.8).







Jul 8, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Nervous disorders
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