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Cerebellar Disease in Horses and Foals
Cerebellar Disease in Horses including cerebellar hypoplasia, abiotrophy, & transient cerebellar dysfunction
Introduction
The cerebellum is a anatomically distinct area of the brain that is responsible for attenuating and fine tuning voluntary movement of the skeletal muscles. Disease of the cerebellum is seen as inappropriate rate, range, and force of head, body, or limb motion. This is seen as exaggerated movement (hypermetria) and may be accompanied by stiffness (spasticity) and intention tremors. Noticeably absent from primary cerebellar disease is weakness and when present suggests lesions of the spinal cord. This article describes the clinical signs, causes, diagnosis, treatment, and prognosis of diseases of the cerebellum.
Clinical Signs
Cerebellar disorders are rare and most often seen in neonates or foals. Horses and foals with cerebellar diseases have a wide based stance and a stiff exaggerated “goose step” walk and trot. Also seen are crashing into fences and falling over backwards. This is important when differentiating from diseases of the brain stem where there is stiffness but the movements are not exaggerated. When moving and particularly when drinking or eating there are tremors, called intention tremors. Normally cranial nerve signs like head tilt or blindness are not present but exceptions exist. Symptoms can appear suddenly or gradually overtime.
There are 4 important diseases of foals:
- cerebellar hypoplasia and
- cerebellar abiotrophy
- transient cerebellar dysfunction
- occipital atlantoaxial (base of the skull and first 2 vertebrae) malformation
Cerebellar Hypoplasia and Abiotrophy
Foals may be affected at birth, but disease often is not evident until 2 to 4 months of age and almost always seen before 6 months of age. Arabian foals seem to be effected, but cases have been identified in several breeds. Cerebellar abiotrophy seems to be associated with an inherited metabolic defect of cortical cerebellar neurons. The result is formation and then premature death of these neurons during late fetal or early postnatal life. The prognosis is poor for recovery and a ridable horse.
Transient Cerebellar Dysfunction
The pathology of this disease is not well described, because given time, foals recover. Foals develop the disease most commonly at a few months of age. Foals afflicted at birth have recovered after a few months of age. Thoroughbreds seem to be affected, but cases have been identified in several breeds. With transient cerebellar disease, the menace response may be normal to slow or missing, but intention tremors often are not present. The prognosis is excellent for complete recovery.
Occipital-Atlantoaxial Malformation
Malformation of the occipital calvarium and/or cervical vertebrae I and 2 occurs. Foals may be affected at birth, but disease often is not evident until a few months of age. Arabian foals seem to be affected, but cases have been identified in several breeds. With occipital atlantoaxial malformation the wings of the atlas often are palpably malformed.
Foals may be born dead or foals may be severely uncoordinated. Dystocia often occurs because on an inability for the unborn foal to align the head with the legs during birth. These horses often posture with the head and neck extended. The prognosis is poor for recovery and a ridable horse.
Other Diseases
Adults and foals can have a primary cerebellar disease from trauma or infection.
Diagnosis
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