Page 229 - Small Animal Internal Medicine, 6th Edition

CHAPTER 10 Pulmonary Hypertension and Heartworm Disease 201

therapy (if there is evidence of cardiovascular shock); and interstitial pulmonary infiltrates; hilar and mediastinal
cough suppressants could be useful. Antibiotics are of ques- lymphadenopathy may also be present. Eosinophilic granu-
VetBooks.ir tionable benefit unless there is evidence of concurrent bacte- lomatosis is treated initially with prednisone (1-2 mg/kg PO
q12h); however, additional cytotoxic therapy (e.g., cyclo-
rial infection. Endothelial changes in survivors regress within
4 to 6 weeks after an adulticide. Pulmonary hypertension and
all dogs respond completely, and relapses are common, espe-
arterial disease, along with radiographic changes, diminish phosphamide or azathioprine) may be necessary as well. Not
over the next several months. Eventually, pulmonary arterial cially when therapy is reduced or discontinued. The response
pressure and the contour of the proximal pulmonary arteries to immunosuppressive drugs after relapse may be poor. Sur-
normalize, although some fibrosis may remain. gical removal of a severely affected lung lobe is a strategy
sometimes used. Therapy for adult HWs is given when pul-
Treatment of Dogs With Complicated monary disease improves.
Heartworm Disease Severe pulmonary arterial disease, including PAH and
PTE, is more common in dogs with long-standing HW
PULMONARY COMPLICATIONS infection, in those with many adult worms, and in active
Allergic or eosinophilic pneumonitis develops in a minority dogs. Severe cough, exercise intolerance, tachypnea or
of dogs with HWD. It tends to develop early in the disease dyspnea, episodic weakness, syncope, weight loss, fever, and
process and is thought to involve an immune-mediated reac- pallor are common clinical signs; sudden death sometimes
tion to dying larvae in the pulmonary microvasculature. occurs. Typical radiographic findings include markedly
Clinical manifestations of HW pneumonitis include a pro- enlarged, tortuous, and blunted pulmonary arteries with or
gressively worsening cough, crackles heard on auscultation, without pulmonary interstitial and alveolar infiltrates; signs
tachypnea or dyspnea, and sometimes cyanosis, weight loss, usually are more severe in the caudal lobes. Marked hypox-
and anorexia. Eosinophilia, basophilia, and hyperglobulin- emia occurs in some cases. Thrombocytopenia and some-
emia are inconsistent findings. HW Ag tests are usually posi- times hemolysis can occur in dogs with severe pulmonary
tive, but many cases do not have circulating microfilaria. arterial disease and thromboembolism; DIC develops in
Diffuse interstitial and alveolar infiltrates, especially in the some dogs. As for postadulticide PTE, treatment with
caudal lobes, are common on radiographs; these can be oxygen, sildenafil, prednisone, strict cage rest, and some-
similar to those in dogs with pulmonary edema, PTE, blas- times a bronchodilator (e.g., theophylline) is indicated to
tomycosis, or metastatic hemangiosarcoma. There is often no improve oxygenation and reduce pulmonary artery pres-
clinically relevant cardiomegaly or pulmonary lobar artery sures. Caution is indicated to avoid systemic hypotension.
enlargement. Tracheal wash cytology usually reveals a sterile Antiplatelet therapy (clopidogrel or aspirin) or anticoagulant
eosinophilic exudate with variable numbers of well-preserved therapy (unfractionated heparin or low-molecular-weight
neutrophils and macrophages. Therapy with a glucocorticoid heparin) could be considered, although benefit of anticoagu-
(e.g., prednisone, 0.5 mg/kg PO q12h) usually results in lation must be weighed against risk of bleeding, particularly
rapid and marked improvement. Prednisone may be contin- in patients with thrombocytopenia or hemoptysis.
ued as needed, in gradually tapered doses (to 0.5 mg/kg After the animal’s condition is stabilized, the typical HW
every other day) and does not appear to adversely affect the treatment protocol can commence as recommended by
adulticide efficacy of melarsomine. the American Heartworm Society (macrocyclic lactone
Pulmonary eosinophilic granulomatosis is an uncommon and doxycycline; 3-injection melarsomine protocol after 2
syndrome that has been associated with HWD, although months).
some affected dogs have negative HW tests. Its pathogenesis
is thought to involve a hypersensitivity reaction to HW Ag RIGHT-SIDED CONGESTIVE
or immune complexes, or both. Pulmonary granulomas are HEART FAILURE
composed of a mixed cell population, with predominantly Severe pulmonary arterial disease and PAH can cause right-
eosinophils and macrophages. A proliferation of bronchial sided CHF. Jugular venous distention or pulsation, ascites,
smooth muscle within granulomas and an abundance of syncope, exercise intolerance, and arrhythmias are typical
alveolar cells in the surrounding area are typical. Lympho- signs; other physical and auscultatory signs secondary to
cytic and eosinophilic perivascular infiltrates may also occur. severe PAH might also occur (see p. 191). Although ascites
Eosinophilic granulomas involving the lymph nodes, trachea, is the most common manifestation of right-sided CHF in
tonsils, spleen, gastrointestinal (GI) tract, and the liver or dogs, pleural or pericardial effusion can occur as well. Car-
kidneys may occur concurrently. The clinical signs of pul- diogenic pulmonary edema is not expected. Treatment is the
monary eosinophilic granulomatosis are similar to those of same as for dogs with severe PAH (sildenafil 1-3 mg/kg PO
eosinophilic pneumonitis. Clinicopathologic findings vari- q8-12h), with the addition of abdominocentesis or thoraco-
ably include leukocytosis, neutrophilia, eosinophilia, baso- centesis as needed, furosemide (e.g., 1-2 mg/kg PO q12h or
philia, monocytosis, and hyperglobulinemia. In some cases, as needed), pimobendan (0.2-0.3 mg/kg PO q12h), an ACEI
an exudative, primarily eosinophilic pleural effusion devel- (e.g., enalapril or benazepril 0.5 mg/kg PO q12h), and mod-
ops. Radiographic findings include multiple pulmonary erate dietary salt restriction. Clopidogrel or aspirin could be
nodules of varying size and location with mixed alveolar and considered, because PTE is one of the major mechanisms of