Sudden onset of cough followed by increasing dyspnoea is characteristic of

Pneumonia,paicularly lobar pneumonia,usually presents as an acute illness with sudden onset fever,chills,rigor,cough and malaise.Cough is characteristically sho,painful and dry,but later accompanied by the expectoration of mucopurulent sputum(rusty coloured in case of Strep.pneumoniae),with pleuritic chest pain.The patients also presents with increasing dyspnoea with increased respiratory rate(>30/min) and use of accessory muscles of respiration. Pleural effusion has got an insidious onset with breathlessness,with or without cough and pleuritic chest pain.In pneumothorax,the most common symptoms are sudden- onset unilateral pleuritic chest pain or breathlessness.In MI,pain is the cardinal symptom with breathlessness,vomiting & collapse. Reference:Davidson's Medicine-22nd edition,page no:683,661,729,590.