1.1.4: Pulmonary parenchymal disease - interstitial disease Flashcards
French heartworm =
Angiostrongylus vasorum
This is a vascular worm; the adults live in the pulmonary arteries.
Describe the life cycle of Angiostrongylus vasorum
Indirect life cycle
Definitive host = dog/wild canids
Intermediate host = slugs/snails
Secondary intermediate/ paratenic host = frogs
Clinical signs of Angiostrongylus vasorum
- Most common: breathlessness / cough
- Bleeding
- Neuro signs
- Often complex signs not limited to respiratory tract
- Often asymptomatic in early stages
- Chronic cough: productive, with occasional haemoptysis
- Dyspnoea
- Tachypnoea
What causes the clinical signs of Angiostrongylus vasorum infection?
Larval migration through lung airway
In heavy burdens, Angiostrongylus vasorum causes hypertension where and what effect does this have on the heart?
Pulmonary hypertension
Pressure within right ventricle increases because it is trying to eject blood into a vascular bed that is full or worms
Dogs with Angiostrongylus vasorum can show prolonged bleeding/ anaemia/ subcutaneous or internal haemorrhage. What tests could you do for this and what would they find?
- Angiostrongylus vasorum can cause immune-mediated thrombocytopaenia ± thrombopathia
- There is prolonged Activate Partial Thrombin Time (APTT)
- There is prolonged Prothrombin Time (PT)
- There are elevated D-dimers/ FDPs which can lead to chronic DIC
Describe the neurological signs you might see with Angiostrongylus vasorum infection
- Paresis
- Seizures
- Depression
- Spinal pain
- Behavioural changes
- Ataxia
- Loss of vision
These signs are associated with aberrant nematode migration or subdural haemorrhage secondary to coagulopathies
Egg deposition/ the presence of L1 A. vasorum leads to:
a) Type III hypersensitivity
b) complement activation
c) granuloma formation
c) granuloma formation
* And also pulmonary inflammation and pulmonary arteriolar vasoconstriction which contributes to pulmonary hypertension.
* There is end arteritis and fibrosis of vessels.
Adult antigens of A. vasorum cause:
a) pulmonary inflammation and granuloma formation
b) Type III hypersensitivity and complement activation
b) Type III hypersensitivity and complement activation
This leads to immune infiltrate into the lungs and other tissues
Why might it be hard to diagnose A. vasorum ?
- Larvae are intermittently shed in faeces
- Take a pooled sample to try and minimise the chances of this
How can you diagnose A. Vasorum ?
- Pooled faecal sample -> L1 in faeces and flotation techniques
- L1 in faeces can be detected by smear methods
- L1 in BAL fluid
- SNAP tests
- PCR on BAL / pharynx swabs
- Supportive evidence: radiograph may show alveolar infiltrates
Describe the radiographic changes you might see with A. vasorum
Mixed alveolar and interstitial pattern
There is haemorrhage into the alveoli, and larval migration through the interstitium
What are the licensed treatments for A. vasorum in dogs?
- Imidacloprid + moxidectin
- Milbemycin oxime + praziquantel
Unlicensed but effective: fenbendazle orally for 7-21 days; levamisole, ivermectin
What are the risks associated with treatment of A. vasorum ? What supportive treatment can you give to mitigate this?
- There is danger associated with treatment - killing lots of parasites at once, releasing lots of antigens at once and thereby provoking host response
- Clotting problems may persist after treatment
Supportive treatment
* Bronchodilators to mitigate airway hyper-responsiveness
* Corticosteroids may reduce tendency for acute deterioration after beginning anthelmintic therapy
* Phosphodiester inhibitors for ongoing pulmonary hypertension
* Cage rest ± oxygen therapy if dyspnoea present
Prevention for A. vasorum
- Moxidectin + Imidacloprid
- Treatment in the PPP prevents establishment of the adult parasites
Signalment for Interstitial Pulmonary Fibrosis (IPF)
IPF a.k.a. Westie lung
* WHWT and other terriers e.g. staffies
* Middle-aged to older dogs
* Seen in cats uncommonly
History suggestive of IPF
- Insidious onset
- Chronic breathlessness which is slowly progressive
- May have coughing - this indicates that there is some degree of airway disease as well
- Exercise intolerance
- Cyanosis
- Syncope
Where can respiratory problems occur and how can we localise them?
- URT obstruction
- Loss of thoracic capacity (pleural space disease)
- Pulmonary parenchymal disease (alveolar or interstitial)
- Non-CRS conditions
Localise using clinical exam and thoracic ultrasound
What clinical exam findings might you get with a terrier with IPF?
- Marked crackles throughout the lung fields - very crackly, more so than alveolar disease
- Prolonged expiratory phase with expiratory effort
What effect might IPF have on the heart and what changes would you see radiographically?
- May see right-sided cardiomegaly (could enter R-sided heart failure)
- This is because the right ventricle has difficulty pushing blood through the fibrous interstitium -> leads to high RV pressure and thus cardiomegaly
- May see “reverse D” on dorsoventral view
What interstitial disease might you see these radiographic changes with?
Interstitial pulmonary fibrosis (IPF)
Diagnosis of IPF
- Suggestive clinical signs: diffuse crackles on auscultation, dyspnoea, coughing
- Thoracic radiographs: generalised interstitial lung pattern (± chronic coexisting lung disease), ± R-sided cardiomegaly, ± pulmonary hypertension (seen as severe alveolar/interstitial pattern)
- CT : “ground glass” appearance with diffuse increased opacity without loss of blood vessels
- BAL : samples are normal or show low cellularity; this helps us rule out other inflammatory conditions e.g. CCB
- Lung biopsy: only definitive method of diagnosis
What clinical/radiographic signs might you see with pulmonary hypertension?
- Generalised / R-sided cardiomegaly/ R HF
- Severe alveolar/ interstitial pattern
- Abdominal distension
- Hepatomegaly
True/false: in an older dog with a heart murmur and breathlessness, you can safely assume the two are likely to be connected and can therefore be treated as the same problem.
False
in older, small breed dogs, heart murmurs and breathlessness should be considered 2 separate problems until you have established a connection between them!
What is the treatment and prognosis for IPF?
- Dog otherwise well but treatment options not great
- Guarded prognosis; survival ~15 months
- Treatment extrapolated from humans depends on form - in dogs likely to be usual interstitial pneumonitis
Symptomatic treatment
* Avoid collars -> harnesses only
* Avoid smoke inhalation
* Inhaled therapy: bronchodilator (unlikely to work), corticosteroids
* Oral therapy: bronchodilators (esp in concurrent airway disease), corticosteroids
* Additional immunosuppressive medication e.g. cyclosporin, azathioprine - NO EVIDENCE of clinical efficacy
* Management of pulmonary hypertension -> phosphodiesterase inhibitors e.g. sildenafil, tadalafil, pimobendan
What drugs could you use to treat pulmonary hypertension?
Phosphodiesterase inhibitors e.g.
* Sildenafil
* Tadalafil
* Pimobendan
Imaging modality? Disease?
CT of a dog with IPF
Lung pattern? Disease?
Interstitial pattern: there is a generalised increase in radiodensity but no border obliteration.
This is from a dog with IPF.
Interstitial pneumonia
Disease affects the interstitium; alveoli and airways are relatively spared.
How might metastatic lung disease present?
- May be an incidental finding
- May present with respiratory difficulty/ tachypnoea
- Usually presents with dyspnoea rather than cough because tumour arrives by haematogenous spread so is in the interstitium not the airways
True/false: all tumours can metastasise to the chest.
False
Not all do. The commonest:
* Osteosarcoma
* Haemangiosarcoma
* Thyroid carcinoma
* Melanoma of mucocutaneous junction
An owner has opted for solitary metastasis removal of a tumour in their dog’s lungs. What diagnostic imaging modality will help you identify how many areas there are and what surgical approach you need to take?
CT
Nodular interstitial pattern
Diffuse interstitial pattern/ disease
