Page 101 - Problem-Based Feline Medicine

7 – THE COUGHING CAT 93

● Serotonin Signs may be episodic (with asthma) or chronic (with
– Serotonin is released from feline mast cell gran- bronchitis).
ules during exposure to an allergen.
There may be a history of exposure to the offending
– Serotonin antagonists are useful in decreasing
allergen, including dusty litter, perfumes, carpet clean-
associated signs.
ers, smoke from fireplaces, cigarette smoke and insula-
– Mast cell stabilizing agents may play a role in
tion materials.
decreasing the severity and frequency of attacks.
● Histamine Cats may present severely air-starved, with cyanosis,
– It has been demonstrated that histamine does not open-mouth breathing, and a significant abdominal
play a role in feline asthma. expiratory push.
– Stimulation of the H3 receptors in the feline air-
way causes relaxation of the airway smooth
muscle, the exact opposite effect seen in
Diagnosis
humans.
– This work might suggest that antihistamines are Many cats with asthma may have eosinophilia on
contraindicated in feline asthma. hematology.
● Leukotrienes
On auscultation, typical lung sounds are wheezes and
– Cats have far fewer leukotriene (LT) receptors in
crackles, which may be worse on expiration.
the airways than do people, but enough are pres-
● Severely affected cats may have diminished air
ent to make a significant contribution to the
sounds from emphysema.
inflammatory cascade.
– Leukotrienes are released from eosinophils, Thoracic radiographs may be normal or abnormal.
and via the lipoxygenase cascade, are converted ● Asthma is characterized by hyperlucency, hyperinfla-
to various forms of leukotrienes, all with vari- tion and flattening of the diaphragm from air trap-
able inflammatory effects. ping.
– Because cats have poor glutathione pathways, ● Chronic bronchitis typically has a diffuse, promi-
the inflammatory leukotrienes LTC4 and LTD4 nent peribronchiolar pattern, with or without patchy
are not produced in significant amounts, but the alveolar infiltrates (especially the right middle lobe
pathway is directed toward LTB4 production. from atelectasis). Right heart enlargement may be
– LTB4 is a known chemotactic agent for present.
eosinophils. ● A lung wash for cytology and culture can be
– Recent evidence questions the role of obtained via transtracheal wash in the awake cat, or
leukotriene in asthmatic cats. using a catheter or bronchoscope to lavage the
– Mast cells have recently been incriminated in bronchi and alveoli in the anesthetized cat, which
having a more profound role is asthmatic patho- is the method preferred by most clinicians. Culture
genesis in humans than previously thought. for mycoplasma should be requested, because
Research is on-going in cats. mycoplasmal infection may cause chronic cough-
ing.
● Cytological examination typically reveals highly
Clinical signs
cellular samples with intact non-degenerative neu-
Signs can occur at any age, although the average is 2–8 trophils as the primary cells. Eosinophils are not a
years. reliable marker because of the increased prevalence
(up to 24%) in the airways of normal cats.
Typically there is a history of coughing for weeks or
Neutrophilic or mixed inflammatory cellular patterns
months. The cough may be mild to severe and inter-
are common.
mittent or continuous. It may be productive and stimu-
● There is on-going research looking for other bio-
lated with coupage of the chest wall.
chemical markers of asthma leukotriene levels,
Dyspnea may range from mild, to severe life-threaten- IgA, IgG and IgE titers, etc., but none is yet clini-
ing respiratory distress from bronchoconstriction. cally available as a test.