ASTHMA-PATHOPHYSIOLOGY AND DIAGNOSIS


PATHOPHYSIOLOGY OF ASTHMA

Current emphasis is on asthma as a "chronic inflammatory disorder of the airways"

  1. Mast cells, eos, PMN, T-lymphocytes
  2. Inflammation leads to airway hyperresponsiveness, resulting in:

 

DIAGNOSIS OF ASTHMA

I. Clinical definition: "recurrent episodes, particularly at night or early am, of the following, with reversible airflow obstruction [as demonstrated by variable nature of sx]":

  1. Cough
  2. Wheeze
  3. Chest tightness
  4. Dyspnea

II. Clear h/o consistent precipitants supports dx (and identifying inhalant allergens will help guide reccs for environmental controls)

III. Family hx supports dx

IV. Px

  1. Hyperexpansion of thorax
  2. Accessory mm. use & nasal flaring, esp. in kids
  3. Wheezing ("wheezing during forced exhalation is not a reliable indicator of airflow limitation")
  4. Prolonged expiratory phase
  5. Increase nasal secrations (evidence of allergic rhinitis), nasal polyps
  6. Evidence of allergic skin disease

V. Spirometry (FEV1, FVC, FEV1/FVC, before & after inhaled bronchodilator)

  1. "Spirometry is needed to establish a diagnosis of asthma"
  2. Demonstrates airflow obstruction and reversibility of same
  3. Us. Can do in kids by ages 4-7
  4. Us. See normal FVC (except in severe asthma w/ air trapping) and reduced FEV1
  5. Spirometric abnormalities aren't sufficient to make dx w/o corroborating sx
  6. PEF not a substitute for spirometry b/c not standardized enough, but can be useful for monitoring

VI. Other diagnostic measures (us. not necessary)

  1. Additional PFT's, esp. if there's a concern re: other coexisting lung disease
  2. PEF at diff. Times of day over 1-2 weeks to detect diurnal variation, esp. in pts with asthma sx but normal spirometry
  1. PEF normally lowest on first awakening, highest sev. Hours before midpoint of waking day; try at these 2 times, with an inhaled short-acting beta-agonist after the morning measurement and before the afternoon measurement; a 20% difference suggests asthma.
  2. Inhalation challenge testing (methacholine or histamine); should be done by trained personnel and not recc'd if FEV1 is < 65% predicted
  3. CXR may be needed to exclude other dx's
  1. Fractional exhaled nitric oxide
    1. An index of lower airways inflammation
    2. In a study in 150 children 6-18yo with cough, dyspnea, and wheezing being evaluated for asthma, a FENO of > 19 parts per billion was 86% sensitive and 89% specific for eventual (at 18mos) diagnosis of asthma-better than FEV1 or percent of eosinophils in induced sputum (J. Pediat. 155:211, 2009-JW)

VII. Exclude alternate diagnoses (diff. dx.)

  1. Vocal cord dysfunction
  1. Can present with severe SOB and wheezing (mostly inspiratory), in rare cases actually causing alveolar hypoventilation
  2. More common in adolescents w/ psychological disorders
  3. Px: monophonic wheeze loudest over the glottis
  4. Flow-volume curve shows inspiratory flow limitation
  5. Treat with speech therapy
  1. In infants and children:
  1. Allergic rhinitis and sinusitis
  2. Foreign body in airway
  3. Vocal cord dysfunction
  4. Vascular rings/laryngeal webs
  5. Tracheal or bronchial stenosis
  6. Viral bronchiolitis
  7. Cystic fibrosis
  8. Bronchopulmonary dysplasia
  9. Cardiac disease
  10. Aspiration from swallowing dysfunction or GERD
  1. In adults:
  1. COPD other than asthma
  2. CHF
  3. Pulmonary embolus
  4. Laryngeal dysfunction
  5. Mechanical airways obstruction, e.g. from tumors
  6. Cough due to meds (e.g. ACEIs)
  7. Vocal cord dysfunction (see above)