Hemihyperaesthesia and hyperresponsiveness resembling central pain syndrome in a dog with a forebrain...

A 4-year-old male Boxer was presented with neurological signs referable to a right forebrain lesion that was confirmed with computed tomography. Whilst characteristic signs of a unilateral forebrain lesion were observed, the dominant and striking finding was a right-sided hemisensory disturbance characterised by hyperaesthesia and hyperresponsiveness. Necropsy revealed a gelatinous mass confined to the right forebrain that was identified histologically as an oligodendroglioma. The lesion was centred on the internal capsule and involved ventral frontal and temporal lobes and the ventrolateral thalamus, including lateral and medial parts of the ventrocaudal nuclear region (ventrobasilar complex) of the thalamus. On clinical and neuroanatomical grounds, the case exhibited features in common with central pain syndrome in human patients with thalamic lesions. These included a somatosensory disorder of hyperaesthesia affecting an entire side of the head and body, behavioural manifestations consistent with spontaneous pain and a lesion involving the ventrobasilar complex. Of interest, the hemisensory abnormality was ipsilateral to the lesion, contrasting with central pain in humans, in which clinical signs are contralateral to analogous lesions. It is suggested that species-specific differences in spinal cord organisation of pain pathways, particularly the greater bilateral projection of nociceptive afferents to thalamic relay nuclei in carnivores, may account for this disparity. Notably, central pain is rare in human patients with brain tumours, even those affecting the thalamus, and this may also be the case in dogs.