Alexander disease in a dog: case presentation of electrodiagnostic, magnetic resonance imaging and histopathologic findings with review of literature

BACKGROUND: Alexander disease is a rare neurodegenerative disorder that has not often been described in dogs. None of the existing descriptions include electrodiagnostic or magnetic resonance imaging workup. This is the first presentation of the results of an electrodiagnostic evaluation including electromyography, motor nerve conduction velocity, F-wave, the brainstem auditory evoked response and magnetic resonance imaging of a dog with Alexander disease. CASE PRESENTATION: A six month old male entire Bernese mountain dog was presented with central nervous system symptoms of generalized tremor, general stiffness, decreased proprioceptive positioning, a reduced menace response, decreased physiological nystagmus, myotonic spasms and increased spinal reflexes which progressed to lateral recumbency. The electromyography revealed normal muscle activity and a decreased motor nerve conduction velocity, temporal dispersion of the compound muscle action potential, prolonged F-wave minimal latency, lowered F-ratio, decreased latency, and lowered amplitude of the brainstem auditory evoked potentials. The magnetic resonance imaging examination revealed ventriculomegaly and linear hyperintensity on the border of the cortical grey and white matter. The histopathological examination confirmed the presence of diffuse degenerative changes of the white matter throughout the neuraxis. A proliferation of abnormal astrocytes was found at the border between the white matter and cortex. There was also a massive accumulation of eosinophilic Rosenthal fibers as well as diffuse proliferation of abnormally large astrocytes and unaffected neurons. CONCLUSION: This is the first histopathologically confirmed case of Alexander disease in a dog with a full neurological workup. The results of the electrodiagnostic and magnetic resonance imaging examinations allow for a high-probability antemortem diagnosis of this neurodegenerative disorder in dogs.