======Approach to Cough======
  * Definitions: Subacute cough: 3–8 wk; Chronic cough: >8 wk
  * Epidemiology: Cough is common symptom-based visit complaint (NHAMCS 2010, cdc.gov)
  * Pathophysiology: Cough receptors found in airways, lung parenchyma, tympanic membranes, esophagus, & pericardium; cough is reflex w/ cortical control (may be initiated or suppressed voluntarily); cough mechanism involves diaphragm, glottis, & muscles of expiration
  * Etiology: Varies by duration, can include airway (upper airway cough syndrome [UACS]), HEENT, GI, and CV causes

=====Evaluation=====
  * General approach: Hx/exam to screen potential etiologies; if none discovered → trial of empiric tx for either UACS (upper airway cough syndrome), asthma, or GERD
  * History: Often nonspecific; ask about onset (post-URI), duration, triggers (after meals—GERD, allergens—asthma); Red flags: Wt loss, hemoptysis, systemic sx
    * Assoc sx: Postnasal drip, sinusitis, hoarseness, reflux sx, edema
    * PMHx: Atopy, GERD, CHF, immunocompromise, CA, TB exposure/RF
    * Meds/toxins: ACEI, βB, smoking status/exposure, occupational/environmental exposures
  * Physical exam: VS: Incl SaO2, HEENT: Auditory canal foreign body, nasal polyps (asthma), cobblestoning (UACS); Pulm: wheezes, crackles; Cardiac: volume overload, valvular disease; Extremities: clubbing
  * Diagnostics: If dx not suggested by above (e.g., ACEI) → CXR; given that most chronic cough 2/2 GERD, UACS, or asthma, may be deferred in nonsmokers until failure of 1st-line empiric tx; further studies (PFTs, CBC, sinus films) as per Ddx (below)

=====Differential Diagnosis=====
  * Subacute cough: Postinfectious cough (48%), infectious sinusitis (33%), asthma (16%) (Chest 2006;129:1142; NEJM 2006;355:2125)
    * Postinfectious cough: Respiratory tract infection → postnasal drip, tracheobronchitis; resolves w/o tx; average duration of bronchitis-associated cough is 24 d
    * Sinusitis: See “Sinusitis”
  * Chronic cough: Often multifactorial; may require tx of multiple causes

^ Etiology ^ Management/Notes ^
| Smoking | Tx: Smoking cessation; see “Tobacco Use” |
| ACEI | Sx can occur 1 wk–6 mo after starting Rx; \\ cough resolves w/in 2–4 wk of discontinuation of Rx | 
| UACS (34%) | Allergic or nonallergic rhinitis, sinusitis \\ Tx: See “Allergic Rhinitis” |
| Cough-variant asthma (28%) | Dx: PFTs (for cough, may start w/ trial of empiric SABA tx) \\ Tx: See “Asthma” | 
| GERD | Dx/Tx: Empiric trial of PPI; see “Gastroesophageal Reflux Disease” |
  
  * Other: COPD, bronchiectasis, eosinophilic bronchitis (dx’ed w/ induced sputum, rx w/ ICS), B. pertussis (see “URI and Influenza”), CHF, ILD, bronchogenic CA, metastatic CA, mediastinal or hilar tumors, allergic alveolitis, lung abscess, EGPA, sarcoidosis, TB, fungal pneumonia (e.g., Cryptococcus), hypersensitivity pneumonitis, allergic bronchopulmonary aspergillosis, habitual cough, foreign body, irritation of external auditory meatus, recurrent aspiration