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EQUINE VETERINARY EDUCATION
Equine vet. Educ. (2019) 31 (5) 242-247 doi: 10.1111/eve.12789
Case Report
Congenital occipitoatlantoaxial malformation in a Warmblood mare H. P. Br€
unisholz†* , N. Wildhaber†, S. Hoey‡, M. Ruetten§, A. Boos¶ and J. M. K€ Keywords: horse; Warmblood; congenital; occipitoatlantoaxial; malformation
Summary A 3-year-old Warmblood mare was presented with spinal ataxia of 3 months’ duration. Clinically, reduced mobility of the neck and a prominent atlas were identified. Neurological evaluation revealed hypermetria, circumduction and reduced proprioception, predominantly in the hindlimbs. Occipitoatlantoaxial malformation (OAAM) was diagnosed based on radiography and computed tomography, and confirmed on post-mortem magnetic resonance imaging and pathological examination. Both the atlas and axis were hypoplastic and dysplastic, and a fusion of the atlanto- occipital joint was found. A dynamic compression of the spinal cord was present at the first and second cervical vertebrae. Histologically, the spinal cord was degenerated due to compression. Furthermore, there were muscular malformations including a fibrotic obliquus capitis cranialis muscle, aplasia of parts of the rectus capitis muscles and presence of additional abnormal muscle. Such muscular abnormalities associated with OAAM have not been reported yet and this is the first report of a case of OAAM in a Warmblood horse.
Introduction
Congenital occipitoatlantoaxial malformations (OAAM) are seldom diagnosed in domestic animals (Mayhew et al. 1978a). Cases have been reported in cattle (Leipold et al. 1972; White et al. 1978; Watson et al. 1985), sheep (Cravero et al. 1976; Van Nie and Folkerts 1977; Schmidt et al. 1993), dogs (Watson 1979; Read et al. 1987; Galban et al. 2010) and cats (Jaggy et al. 1991), but the vast majority of cases have been described in horses (Schmaltz 1915; Leipold et al. 1974; Mayhew et al. 1978a; Watson et al. 1985; Wilson et al. 1985; Watson and Mayhew 1986; deLahunta et al. 1989; Gonda et al. 2001). Anatomical abnormalities associated with OAAM can be
found in the occiput, atlas (C1) and axis (C2). The most commonly encountered malformations include abnormalities of the occipital condyles, fusion of occiput and C1, incorrect localisation and development of C1 and a hypoplastic denticular process (dens) of C2 (Leipold et al. 1974; Mayhew et al. 1978a; Jaggy et al. 1991; Schmidt et al. 1993; Rush 2012). Clinical signs are variable, ranging from mild ataxia to tetraplegia and may become more severe with increasing patient age (Mayhew et al. 1978a). The Arabian horse is the most common breed affected by OAAM. In this breed, OAAM is inherited in an autosomal
recessive manner without a sex predilection (Noden and deLahunta 1985; Watson and Mayhew 1986). Isolated cases have been reported in Appaloosas, Quarter Horses, Morgan Horses and Standardbreds (Mayhew et al. 1978a; Wilson et al. 1985). Although Warmblood horses represent one of the most widespread breed, the authors are unaware of any literature describing OAAM in Warmbloods. The purpose of this case report is to describe a case of congenital OAAM in a Warmblood horse.
Case details
History A 3-year-old Swiss Warmblood mare was referred to the Equine Hospital, Vetsuisse Faculty, University of Zurich, Switzerland with a 3-month history of ataxia. The horse had been bred by the current owner who reported a normal development until the mare was due to be broken and trained. At this time, the owner noted an atypical swaying of the hindlimbs with an increased range of motion of the pelvis whilst trotting. The owner suspected a luxation of the hip to be the origin of the problem. No history of trauma was reported, although this cannot be excluded completely as the mare had been kept on pasture together with other horses. At the age of 1.5 years, the horse had been presented to a veterinarian for a fetlock laceration and no neurological deficits had been noted on that occasion.
Clinical examination At presentation, the mare was in excellent body condition. Rectal temperature, heart rate and respiratory rate were within normal ranges. The head was carried in an extended position (Fig 1) and a prominent C1-C2 area was visible. Palpation of the neck revealed bilateral
painful protrusions at the C1-C2 region. Active neck flexibility was moderately reduced to both sides. The mare showed a generalised ataxia at the walk and trot that was graded as 2 out of 5 (Mayhew et al. 1978b) in the forelimbs (moderate dysmetria, hypermetria and proprioceptive deficits) and 3 out of 5 in the hindlimbs (severe dysmetria, hypermetria and proprioceptive deficits, moderate toe dragging and circumduction). Walking the horse with its chin lifted exacerbated the ataxia and whilst backing a tendency to buckle was observed in the hindlimbs. There was no evidence of cranial nerve deficits.
ummerle†
†Equine Department, ‡Section of Diagnostic Imaging, and ¶Institute of Veterinary Anatomy, Vetsuisse Faculty, University of Zurich, Zurich; and §PathoVet AG, Tagelswangen, Zurich, Switzerland. *Corresponding author email:
hbruenisholz@vetclinics.uzh.ch
© 2017 EVJ Ltd
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