Nigropallidal encephalomalacia in horses grazing Rhaponticum repens (creeping knapweed)

Abstract

Nigropallidal encephalomalacia was diagnosed in two horses in northern Victoria that had a history of long-term pasture access to a dense growth of Rhaponticum repens. The region in which the affected horses lived had received well above average rainfall for several months preceding the poisoning. Affected horses had sudden onset of subcutaneous oedema of the head, impaired prehension and mastication, dullness, lethargy and repeated chewing-like jaw movements. Diagnosis was confirmed at necropsy, with characteristic malacic lesions in the substantia nigra and globus pallidus of the brain. This is the first documented case of nigropallidal encephalomalacia in Australian horses associated with R. repens.

Cryptic etiopathological conditions of equine nervous system with special emphasis on viral diseases

“…The pathological conditions associated with nervous system of equines can be classified on the basis of the etiological agents involved (viral, bacterial, parasitic, fungal, algal, and plant toxins/mycotoxins) or by anatomical location of lesions, e.g., hepatic encephalopathy (hepatotoxic plants causes damage to cerebral cortex and basal nuclei) [ 6 , 7 ]; nigropallidal encephalomalacia mainly due to the consumption of Rhaponticum repens (creeping knapweed) (leads to destruction of nigrostriatal pathways causing dopamine deficiency), are the conditions mainly involving the brain [ 7 , 8 ] while arboviral encephalomyelitis such as Eastern equine encephalitis (EEE), Western equine encephalitis (WEE), Venezuelan equine encephalitis (VEE), and West Nile fever (WNF) [ 9 ], rabies, pelvic limb paralysis [ 10 ], and equine protozoal myeloencephalitis [ 11 ], mainly affect brain stem and part of spinal cord [ 6 ]. Equine motor neuron disease and wobbler disease (incoordination) [ 12 ], affect spinal cord, while stringhalt [ 13 ], laryngeal hemiplegia (racing thoroughbred horses) [ 6 , 14 ], and polyneuritis equids (caused by Halicephalobus gingivalis ) are associated with nerves and ganglion affections.…”

Equine skull magnetic resonance imaging: The where, when and why?

“…; Javsicas et al . ; Elliott and McCowan ). While macroscopically normal intracranial examinations are relatively common ( Fig a ), it is this author's experience that many clinicians and horse owners have difficulty reconciling such findings in a horse with visibly serious neurological signs.…”