4.6 Common Medical Conditions Resulting in Behavioral Signs
4.6.1 Anxiety Disorders
Anxiety is the emotional response that occurs when there is the anticipation of future danger. What is critical for animal caretakers to be aware of is that the danger does not have to be real; it may be unknown or imagined. Equally important is that when animals perceive something to be dangerous or threatening, that is what they will respond to emotionally. The physiological responses to feelings of anxiety are similar to the responses that are seen with fear (see Box 4.2). Many of these behaviors can also be seen associated with particular medical conditions, further complicating some diagnoses.
In addition, it appears that some individuals have behavioral dysfunction due to pathological anxiety, and this results in maladaptive behavior. A definition for pathological anxiety has been proposed: “Pathological anxiety is a persistent, uncontrollable, excessive, inappropriate and generalized dysfunctional and aversive emotion, triggering physiological and behavioural responses lacking adaptive value. Pathological anxiety‐related behaviour is a response to the exaggerated anticipation or perception of threats, which is incommensurate with the actual situation” (Ohl et al. 2008).
Box 4.2 Behavioral Signs of Anxiety
Panting
Pacing
Trembling
Salivating
Increased blood pressure
Increased heart rate
Increased respiratory rate
Dilated pupils
Avoidance behaviors such as hiding
Hypervigilance
General behavioral arousal
Irritability
Restlessness
Freezing or tonic immobility response
Increased aggression or threatening behaviors
Sleep‐wake cycle disturbances
Lowered body posture (crouching)
Lowered ears
Tucked tail
Repeated lip or snout licking
Yawning
Differentiating pathological anxiety from the situational anxiety that might be expected in an animal that has recently been introduced into a shelter situation will not be easy as the line between normal and abnormal is often vague. However, caretakers should remain aware that some animals will not adapt well to the shelter environment due to preexisting behavioral pathology. In addition, the behavioral pathology may predispose these animals to illness and poor welfare due to the chronic stimulation of the HPA axis and the animal’s inability to adapt to the changing environment. Lastly, anxiety can occur as a result of any disease process, pain, or discomfort, especially if it remains unidentified by caretakers and thus untreated.
4.6.2 Neurological Disorders
A variety of different neurological disorders have the capability of affecting behavior in a variety of different ways. While many neurological disorders are steadily progressive and, thus, will eventually present additional non‐behavioral signs, in many cases, behavioral changes will precede the appearance of other more severe neurological signs by weeks or even months. Storage diseases, neoplasia, inflammatory conditions, degenerative conditions, toxicosis, malformations, ischemia, and infections can all lead to changes in behavior.
The location of a brain lesion will dictate the associated behavior changes. The limbic system, whose structures lie deep within the brain, functions to control memory, emotions, and basic drives such as sexual activity, anxiety, and feelings of pleasure. Damage to the limbic system can result in personality changes, including increases in fearfulness and aggressive behavior. In other cases, seizures may result. The forebrain, including the prefrontal area, is the part of the brain associated with cognitive behavior, motor planning, thought, and perception. Forebrain lesions can lead to changes in temperament, loss of previously learned behaviors, and failure to recognize or respond appropriately to environmental stimuli. Lesions of the brain stem or forebrain may lead to changes in awareness or consciousness and mentation. Animals with brain stem lesions may demonstrate altered responses to stimuli, dullness, and stupor and may become comatose (Lorenz et al. 2011).
4.6.2.1 Neoplasia
Intracranial neoplasia can be either primary or secondary, and, depending on the location within the brain and the character of the tumor, brain neoplasia can result in several different behavioral changes. Primary brain tumors originate from cells within the brain and meninges and are more likely to result in insidious, slowly progressive effects, whereas secondary tumors resulting from metastatic disease will usually result in acute changes.
Seizures, while the most recognizable, are not always the most common sign of a brain tumor. Other early behavioral and clinical signs of a brain tumor such as changes in behavior and mentation, visual deficits, circling, ataxia, head tilt, and cervical spinal hyperesthesia are often not appreciated. Reluctance to climb stairs, pacing, standing in corners, stumbling over objects, housesoiling, and agitation may also be seen.
4.6.2.1.1 Dogs
Primary brain tumors in the dog may include meningioma, astrocytoma, neuroblastoma, oligodendroglioma, and ependymoma, to name a few. Dogs with brain tumors are usually presented with concurrent neurologic deficits, but one study found that when brain tumors developed in the rostral cerebrum, behavioral changes commonly occurred prior to the appearance of other neurologic deficits (Foster et al. 1998). These changes were described as dementia, aggression, and alteration in established habits. Many of the dogs in the study, but not all, also had seizures, but 72% of them had no neurological deficits on presentation. Neurological deficits eventually appeared in all cases, with some taking up to three months to appear (Foster et al. 1998). Meningiomas, the most common primary brain tumor in dogs, usually occur in dogs more than seven years of age but have been seen in dogs as young as 11 weeks. Behavioral signs may include increases in aggression, head pressing, circling, housesoiling, pacing and panting (common signs of agitation), vocalizations, seizures, and changes in mentation.
While neoplasia in dogs younger than six months occurs less often, the brain is the second most common site for it to develop, so age alone cannot always rule out the possibility of a brain tumor. However, brain tumors occur most often in dogs more than five years of age.
4.6.2.1.2 Cats
Meningiomas are also the most common tumor of the feline brain and have been documented in cats as young as one year of age. Geriatric cats with meningioma have been presented to their veterinarian with the owner complaint of “just not being themselves” (Sessums and Mariani 2009). Clinical signs that have been reported include reluctance to play, episodic lethargy, and aggression. One owner reported apparent pain when she touched her cat’s head, three months prior to presentation with other clinical signs (Karli et al. 2013).