Comparison of gluteus medius muscle activity in Haflinger and Noriker horses with polysaccharide storage myopathy

Type 1 polysaccharide storage myopathy caused by genetic mutation in the glycogen synthase 1 gene is present in many breeds including the Noriker and Haflinger horses. In humans, EMG has already been used to document changes in the muscle activity patterns of patients affected by human glycogen storage disorders. Therefore, the aim of the present study was to describe gluteus muscle activity with surface electromyography (sEMG) in Haflinger and Noriker horses with known GYS1 mutation status during walk and trot. Thirty-two horses (11 Haflinger and 21 Noriker horses) with homozygous non-affected (GG), heterozygous affected (GA) and homozygous affected (AA) status of GYS1 mutation without overt clinical signs of any myopathy were selected for the current study. Using surface electromyography gluteus medius muscle activity at walk and at trot was measured, and muscle activity was described in relation to the maximum observed value at the same sensor and the same gait. In order to further describe the signals in detail comprising both frequencies and amplitudes, the crossings through the baseline and the 25, 50 and 75 percentile lines were determined. The result of the relative muscle activity did not show a consistent difference between affected and non-affected horses. Genetically affected (GA and AA) horses showed significantly less density of muscle activity for both gaits and horse breeds except for the crossings per second at the baseline and 75 percentile at walk in the Haflinger horses and 75 percentile at trot in the Noriker horses. The medians of all calculated density values were significantly lower in the GA Haflingers compared to the GG Haflingers (p = 0.012) and also in the AA Norikers compared to the GG Norikers (p = 0.011). Results indicate that the GYS1 mutation reduces the number of functional muscle fibres detected by sEMG measurements even in the absence of overt clinical signs.     

Skeletal metastasis from a squamous cell carcinoma of the nictitating membrane in a Haflinger horse

A 12-year-old Haflinger gelding with a history of a persistent cough was referred for evaluation of a severe lameness of the left forelimb. An excision of the right nictitans had been performed 2 years prior to presentation, and a squamous cell carcinoma (SCC) with embolic neoplastic cells in several blood vessels had been confirmed by histopathology. The origin of the lameness could not be localised with regional analgesia; therefore, a nuclear scintigraphic examination was performed. This revealed an area of marked increased radiopharmaceutical uptake at the level of the caudodorsal border of the left scapula. Further examination, including ultrasound-guided biopsy of the suspect region, confirmed the presence of SCC invading the scapula. Due to poor a prognosis, the horse was subjected to euthanasia. Prior to euthanasia, the gelding was tested homozygous for the missense variant in the damage-specific DNA-binding protein 2 (DDB2) gene, which is reported as a risk factor for the development of nictitans SCC in Haflinger horses. Post-mortem evaluation revealed multiple SCC metastasis, affecting the scapula, the liver and the lungs. To the authors' knowledge, this is the first reported case of bone metastasis following a primary periocular SCC in a horse.