Background Information of Clinical Importance
Anatomy and Physiology
An atlas of the caprine brain in 23 transverse sections has been published (Yoshikawa 1968). The gross anatomy of the caprine central nervous system (CNS) and peripheral nerves has been described elsewhere and compared with sheep and cattle (Dellmann and McClure 1975; Godhinho and Getty 1975; Ghosal 1975).
Published studies on the neurophysiology of goats are uncommon and no neurophysiologic attributes of clinical importance unique to the species have surfaced.Thalamic melanosis has been reported frequently as an incidental finding at post mortem in goats with brown haircoats and occasionally white coats, but has no clinical significance (Bestetti et al. 1980). One anomaly of the goat that could affect the clinical evaluation of the nervous system is a high frequency of variation in vertebral body numbers and the occurrence of transitional vertebrae (Simoens et al. 1983). This variation can complicate the technique of cerebrospinal fluid (CSF) collection at the lumbosacral site and confuse interpretation of spinal radiographs and myelography. Details concerning vertebral anomalies are given in Chapter 4.
Neurologic Examination
The small size and reasonably cooperative nature of goats facilitate the performance of a thorough neurologic examination. A consistent, systematic approach should be taken. Protocols and procedures for neurologic evaluation of small ruminants have been published and are similar to those used in small animal medicine (Brewer 1983; Constable 2004). The examination must always include assessments of five major factors: mental status and behavior, cranial nerve functions, postural reactions, locomotion, and spinal reflexes. A summary of the types of signs associated with lesions in different regions of the CNS is given in Table 5.1 and details of the evaluation of cranial nerve function are given in Table 5.2.
Cerebrospinal Fluid Analysis
Analysis of CSF can be used to diagnostic advantage in caprine medicine (Smith 1982). Two sites, atlanto-occipital and lumbosacral, are routinely used for collection of CSF from the subarachnoid space. Heavy sedation or general anesthesia of the goat is required to accomplish an atlanto- occipital tap. Several methods have been recorded, including use of intravenous (IV) diazepam (5-10 mg total dose), intramuscular (IM) xylazine at a dose of 0.1 mg/kg bodyweight (bw), IV thiopental sodium at a dose of 15 mg/kg, or inhalation anesthesia with halothane (Brewer 1983; Chandna et al. 1983). The lumbosacral tap may be accomplished using tranquilization or, if the risks of medication are high, manual restraint. A lumbosacral CSF tap without chemical restraint is best attempted only in comatose, paralyzed, or severely paretic goats. Because abnormal CSF is not necessarily homogeneous in character, the site of collection should be closest to the suspected lesion to maximize the value of the sample. Regardless of the site selected, the procedure should be done using strict aseptic techniques to avoid iatrogenic meningitis.
For atlanto-occipital puncture, the goat is laid in lateral recumbency. The head is flexed at a right angle to the cervical spine and positioned so that the head and neck are in a single plane parallel to the ground or table. This extreme flexion of the neck may compromise air movement through the trachea, particularly when a flexible tracheal tube is in place. The site of skin penetration is on the dorsal midline at the point of intersection with an imaginary line connecting the anteriormost aspects of the wings of the atlas. Ideally, a styletted, 2.5 in. (6.4 cm), 20-gauge spinal needle should be used, but an ordinary 1.5 in. (3.8 cm) 20- or 22- gauge disposable needle can be used if necessary (Brewer 1983). The needle should be directed toward the lower jaw as it penetrates the skin. The usual depth to the
Table 5.1 Clinical signs associated with lesions in different regions ofthe nervous system.
| Region of nervous system | Clinical signs possibly observed |
| Autonomic nervous system | Miosis or mydriasis, salivation, increased or decreased gut motility, changes in fecal and urinary continence, muscle twitching |
| Cerebrum | Changes in mental status, mania, hyperexcitability, hysteria, depression, nonresponsiveness, coma Changes in behavior, convulsions, opisthotonos, head pressing, teeth grinding, constant chewing or vocalizing, yawning, inability to chew, blindness with normal pupillary responses Changes in gait, compulsive walking or circling, contralateral proprioceptive deficits |
| Cerebellum | Incoordination with no accompanying weakness, hypermetria in all limbs, wide-base stance, possible intention tremors, loss of menace response (also involves cranial nerves, cerebrum, and brain stem) |
| Vestibular system Brain stem | Ipsilateral head tilt, circling, hemiparesis with staggering gait, resting nystagmus Ipsilateral weakness, incoordination, spasticity, proprioceptive deficits |
| Cranial nerves | Deficits in vision, smell, hearing, or swallowing; changes in tone, motor control, or sensation of facial structures; abnormal eyeball position; carriage of head or balance |
| Spinal cord C1-C6 | Incoordination and weakness in affected limbs with loss of proprioception, potentially all four limbs affected, usually worse in hindlimbs; reflexes are hyperactive in all affected limbs; skin sensation diminished in affected dermatomes |
| Spinal cord C7-T2 | Incoordination and weakness in affected limbs with loss of proprioception, forelimb deficits often equal hindlimb deficits; hyporeflexia of forelimbs, hyperreflexia of hindlimbs; loss of skin sensation in affected dermatomes |
| Spinal cord T3-L3 | Incoordination, weakness, and loss of proprioception in one or both hindlimbs; hindlimb reflexes hyperactive; forelimbs normal in all respects; loss of skin sensation in affected dermatomes |
| Spinal cord L4-S2 | Incoordination, weakness, and loss of proprioception in one or both hindlimbs; hyporeflexia of hindlimbs; forelimbs normal in all respects; loss of skin sensation in affected dermatomes |
| Spinal cord S1-S3 | Distended bladder and loss of anal and tail tone; caprine spinal cord ends at spinal cord S3 and subarachnoid space extends to second caudal vertebra |
| Peripheral nerves | Deficits of extension, flexion, or adduction; muscle atrophy in a single limb; localized loss of skin sensation on affected portions of limb; possible hyporeflexia |
| Neuromuscular junctions | General weakness, muscle twitching, or tremors |
C, cervical spinal segment; L, lumbar spinal segment; S, sacral spinal segment; T, thoracic spinal segment.
subarachnoid space is 2.5-3.8 cm (1-1.5 in.), but the needle should not be passed the full depth without stopping frequently to remove the stylette and check the progress. The advancing needle should remain perpendicular to the dorsal midline to avoid hemorrhage from entering the paravertebral venous sinuses.
The CSF should rise readily up the needle when the subarachnoid space is reached and the stylette removed. The fluid may be allowed to drip into a collecting tube, or aspirated gently with a syringe. If it runs forcefully from the needle, this may suggest increased CSF pressure, and rapid egress or aspiration of fluid could result in caudal herniation of the brain. A manometer can be attached to the needle hub via a three-way stopcock to record CSF pressure. If CSF pressure is not increased, up to 0.22 mL of CSF/kg of bw may be extracted safely. On average, the total volume of CSF in adult goats is 20-25 mL, 8-12 mL of which is in the ventricles (Pappenheimer et al. 1962).
For a lumbosacral tap, the animal is restrained in lateral recumbency and the spine markedly flexed, with the plane of the midline parallel to the supporting surface. The puncture site is located on the dorsal midline, where it intersects an imaginary line connecting the anteriormost aspects of the two tuber sacrale. There is frequently a palpable depression in the skin at this point. A local skin block of the puncture site with lidocaine is advised if the goat is not sedated. The occurrence of transitional lumbosacral vertebrae may make it difficult to identify and penetrate the lumbosacral space in goats. If frequent attempts are met with failure, the tap should be attempted in the L5-L6 intervertebral space. This is accomplished by palpating the two caudal- most dorsal spinous processes identifiable cranial to the
Table 5.2 Evaluation of cranial nerve function in goats.
| Activity, condition, or test response observed in normal goats | Cranial nerves and other components of nervous system responsible for normal activity, condition, or response |
| Goat can see | II, cerebrum, connecting pathways, eye |
| Normal menace response (eyelids close in response to noncontact threatening gesture) | II, VII, cerebrum, cerebellum, brain stem |
| Bilaterally similar pupil size | II, III, sympathetic nervous system, brain stem |
| Normal pupillary light response | II, III |
| Eyes normally positioned in head | III, IV, VI, VIII |
| Eyeball retracts when cornea is touched | III, V, VI |
| Jaw tone and nostril sensation are normal | V |
| Eyelids close when canthus is touched | V, VII |
| Ear twitches when inside of ear is touched | V, VII, X |
| Lips retract when probe is introduced into commissure of lips | V, VII |
| Nostrils held symmetrically and move normally | VII |
| Ears held in normal position | VII |
| Eyelids held open normally | III, VII, sympathetic nervous system |
| Goat responds to sound | VIII |
| Head is held in normal position | VIII, cerebrum |
| Eyeballs drop slightly and evenly when head is tilted upward | VIII |
| Normal vestibular nystagmus is seen when head is turned to side, fast component is toward turned side | III, IV, VI, VIII, brain stem |
| No spontaneous nystagmus is observed | VIII |
| Swallowing and tongue movement are normal | IX, X, XII |
| Tongue tone is normal | XII |
I, olfactory nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve; VIII, vestibulo-cochlear nerve; IX, glossopharyngeal nerve; X, vagus nerve; XI, spinal accessory nerve; XII, hypoglossal nerve.
sacrum and passing the needle between them on the midline, just anterior to the more caudal spinous process.
The L4-L5 space can be used similarly.A technique for placement of a styletted, stainless steel cannula in the third ventricle of the goat under anesthesia has been described (Mogi et al. 2003). This allows for repeated collection of CSF during research studies requiring multiple samples over time.
Some interpretation of the CSF is possible without laboratory support. Normal CSF is clear and colorless. Cloudiness suggests inflammation caused by increased cells or protein. Xanthochromia, or yellow discoloration, suggests earlier presence of blood in the CSF, frequently associated with trauma. Increased CSF pressure may be recorded in cases of PEM, hydrocephalus, or other causes of cerebral edema. Reagent test strips designed for urinalysis may be applied to CSF in the field (Brewer 1983). Protein content more than 1+ is abnormal, blood should not be present, and the absence of glucose may suggest bacterial meningitis. Blood could be present, as a result of contamination by a traumatic tap.
Normal laboratory values reported for cellular and chemical constituents of caprine CSF are given in Table 5.3. Glucose levels in the CSF are normally 60% of those in blood. If xylazine is used to sedate goats for a CSF tap, glucose concentration in the CSF may double within 30 minutes of administration (Amer and Misk 1980).
Imaging Techniques
Plain radiography is useful to identify bony lesions that may affect the integrity of the brain and spinal cord. Myelography can aid in identification and localization of intramedullary and extramedullary lesions of the spinal cord and meninges. Preparation and positioning of goats for myelography are similar to those described above for the CSF tap, and procedures and applications for myelography of goats at both the atlanto-occipital and lumbar sites have been described (Chandna et al. 1978; Rowe 1979; Chandna et al. 1983). Cerebral angiography has been used in goats to assist in the diagnosis and surgical treatment of
Table 5.3 Selected normal values for constituents of cerebrospinal fluid of goats.
| Constituent | Unit | Mean | Range (or ±standard deviation) | Reference |
| Aspartate aminotransferase | IU/L | 79.8 | (±27) | Aminlari and Mehran (1988) |
| Calcium | mg/dL | 4.6α | Kaneko (1980) | |
| mg/dL | 9b | 5.5-14.5 | Cissik et al. (1987) | |
| Chloride | mEq/L | 116-130 | Cissik et al. (1987) | |
| Glucose | mg/dL | 56 | Fletcher et al. (1964) | |
| mmol/L | 1.8 | (±0.8) | Aminlari and Mehran (1988) | |
| Lactate dehydrogenase | IU/L | 8.9 | (±9.3) | Aminlari and Mehran (1988) |
| Magnesium | mg/dL | 2.4 | 1.7-3.2 | Cissik et al. (1987) |
| Pandy testc | negative | negative | Brooks et al. (1984) | |
| pH | 7.3-7.4 | Brooks et al. (1984) | ||
| Phosphorus | mg/dL | 11.6 | Brooks et al. (1984) | |
| Potassium | mEq/L | 3 | Kaneko (1980) | |
| Sodium | mEq/L | 131 | Kaneko (1980) | |
| Specific gravity | 1.005 | 1.004-1.008 | Fletcher et al. (1964); Brooks et al. (1984) | |
| Total protein | mg/dL | 12 | 0.0-45 | Smith (1982); Kaneko (1980); Brooks et al. (1984) |
| mg/dL | 29.6 | (±15.1) | Aminlari and Mehran (1988) | |
| Urea | mg/dL | 5-6.2 | Brooks et al. (1984) | |
| White blood cellsd | #/mm3 | 0-9 | Smith (1982); Fletcher et al. (1964) |
a Characteristics of goats not specified.
b Pregnant does only, n = 20.
c The Pandy test is a semiquantitative precipitation test that identifies the presence of globulin in the cerebrospinal fluid. Normally there is no globulin present.
d Cells normally present may be lymphocytes, macrophages, or intact neutrophils. Red blood cells are not found in the normal caprine cerebrospinal fluid.
coenurosis (Sharma et al. 1974). Scintigraphy with radiolabeled 99mTc-ciprofloxacin was used as a diagnostic aid in a case of vertebral osteomyelitis and diskospondylitis in a 3-week-old goat with acute hindlimb paresis (Alexander et al. 2005). Image quality was best four hours after injection of the radiolabeled drug.
A topographic study of the cranioencephalic structures of the goat using computed tomography (CT) has been reported (Arencibia et al. 1997), though the use of CT in clinical practice has been limited in goats. CT has been used as a diagnostic aid in a case of paraplegia in an adult Boer goat (Levine et al. 2006). The scan revealed the presence of disko- spondylitis and a compressive myelopathy. CT was also employed in the diagnosis of a glioma in the right frontoparietal cortex of the brain of an adult male goat that presented with a one-week history of circling (Marshall et al. 1995).
Magnetic resonance imaging (MRI) has been used to identify spinal cord compression due to a mass in the lumbar region of an adult goat with paraparesis (Gygi et al. 2004). At necropsy the mass was determined to be a lymphosarcoma. MRI was also used to identify lesions in the thoracic segment of the spinal cord of a 5-month-old goat with posterior paresis in support of a diagnosis of the neurologic form of CAE (Steiner et al. 2006). The use of MRI was reported as an aid in the diagnosis of PEM in a 2-month-old Boer goat kid, identifying bilateral symmetrical high-water-content lesions of the frontoparietal cortex (Schenk et al. 2007).
Electroencephalogram
The normal electroencephalogram (EEG) of goats has been recorded in varying states of consciousness and in reference to rumination (Sugawara 1971; Bell and Itabisashi 1973). The EEG of goats also has been recorded under experimental disease conditions, including urea poisoning (Itabisashi 1977) and Bermuda grass-induced tremors (Strain et al. 1982), as well as in a clinical case of partial epilepsy in an adult Nubian doe (Olcott et al. 1987) and in a group of goats with pulaltve Solanum viarum toxicity (Porter et al. 2003).
Several physiologic studies have also included recordings of the EEG in goats (Sugawara et al. 1989; Bergamasco et al. 2005, 2006). Determination of the bispectral index of the EEG was reported to be useful in monitoring the depth of isoflurane anesthesia in goats (Antognini et al. 2000). The use of visual-evoked brain stem potentials (VEP) and electroretinograms (ERG) in the clinical assessment of PEM in a goat has been reported. The ERG was normal, but the VEP was abnormal in the acute phase of disease when the goat was clinically blind. At one year post treatment, vision was restored and the VEP showed an almost normal recording (Strain et al. 1990).