history of present illness is a very important part of your history taking and it should include three main things that is the three c's that it should include first is what is the system involved that is what is the case so whenever a patient comes with a symptom you first need to know what is the system involved like if it is a cardiac it is a respiratory it is git it is cns it is renal or it is endocrine or any hematological cause so you need to localize what is the system involved and we will say that what is the case first c is what is the case the second is you need to know what is the cause that is if the let's say the patient has respiratory system involvement what is the disease that is occurring in that system that is causing this symptom and the third is the complication that is if there are any complication due to the disease that the patient is suffering from we will try to understand this with the help of an example so let's say the patient comes with breathlessness so first we need to check what is the system involved the two main systems that can lead to breathlessness is one is a cardiac cause one is a respiratory cause so one first we have to know if the system involved is a respiratory or it is a cardiac for that we will have to ask the cardinal features of each of the system involvement like for cardiac system if there is breathlessness present it is usually associated with paroxysmal nocturne dyspnea orthopnea palpitations chest pain syncope or pedal edema whereas in case of a recipe system involvement there will be usually history of preceding cough and sputum and may be associated with these or hemoptysis so you need to ask all this history and need from that you need to evaluate which system is involved for example in this case the patient that we took in that case the patient had initially symptoms of cup with sputum and it was followed by breathlessness whereas there are no cardinal features of cvs like there is no pnd north of near no palpitation so we have evaluated that probably respiratory cause respiratory system is being involved so the first point is clear that is the case is probably respiratory now we need to know what can be the cause of breathlessness in this respiratory cause for this you need to know that whenever a system is involved there can be different causes or different diseases that can be involved for this you can learn a simple mnemonic that is vitamin cd that is for any system involvement the cause can either be vascular or infectious or traumatic autoimmune allergic metabolic which includes endocrine nutritional electrolyte hydrogenic idiopathic neoplastic congenital or drugs and toxins okay for example in this case we have localized that the system is respiratory so the vascular cause for respira the vascular cause in respiratory system that can cause breathlessness is pulmonary embolism the infectious cause can be pneumonia lung abscess bronchitis or a plural effusion the traumatic cause can be pneumothorax and the autoimmune cause can be interstitial lung disease or pleural effusion the allergic cause can be asthma the neoplastic cause can be a lung tumor the congenital cause may be cystic fibrosis congenital diaphragmatic hernia and the toxin that can lead to breathlessness is chronic smoking so while evaluating the cause you have to take history regarding all these causes so that you can know which causes exactly patients suffering from for example if as this case is a respiratory case we will have to ask history of if there is any history of dvt or immobilization to rule out pulmonary embolism you will take if patient has any fever any sputum any foul smelling sputum or a historic tv contact to rule out an infection you can take history of trauma to rule out pneumothorax history of alopecia oral ulcer skin rash or joint pains to rule out if there is any autoimmune cause for asthma you can check if the patient has any allergen exposure or patient has associated exima rhinitis conjunctivitis or a family history of asthma for neoplastic causes you can ask if the patient has constitutional weight loss anorexia or the patient has any paraneoplastic symptoms or any symptoms of metastasis similarly for congenital cause you can ask if the symptoms are present since birth or if there is any family history present similarly for drugs and toxin you can ask for the history of any toxin or drug exposure so in this case we have suspected that the patient had breathlessness due to a respiratory cause and the patient has a history of chronic smoking and has history of chronic progressive breathlessness with acute exacerbation so you probably we are going into the lines of now copd so first what we did is we checked what is the case that is what is the system involved by asking the cardinal features and then to know what is the cause i asked history of every point of vitamin cd to check what is the cause once we have come to know what is the cause now we have to know if the patient has the disease if there are any complications due to it because the management will depend on it also so let's say in this case the patient is copd and copd can lead to acute exacerbations or a multifocal lateral tachycardia or a respiratory failure type 2. so in this case we will ask history to rule out if there are any complications present like we will ask if there is any history of acute attacks of fever purulence bottom for which the patient might have been hospitalized or if the patient has any history of palpitations or if the patient has any history of morning headache abnormal behavior altered sleep altered sensorium or edema and another one which where another important complication that can occur is the core pulmonal it can also occur for that we can check if the if we can ask the patient if there's any patel edema or if there is any jaundice or if the patient has any distended veins so by this you can know that if the patient has any complications or not so finally as a for any symptom it can be any symptom for you should know what is the case that is what is the system involved it can be recipe cvs git endo renal hematological for this what you need to know what will you do we will ask for cardinal features so you need to read cardinal features of all the systems that what are the symptoms that point out this to this system second is what is the cause for this what you can do is you can remember the mnemonic vitamin cd and rule out all options by asking history for each and third is the complication complication you need to know what can be the different complication occurring in different diseases like in this case we have discussed for a copd in let's say if the patient has any serious cause then the complication might be either the patient might have infective endocarditis or the patient might have arrhythmias so you have to ask history for these things so if you know what are the cardinal features of each system you remember well the vitamin cd of all systems all causes and you remember what are the complications that can occur for the each symptom in that case you can take a good hopi and you will surely never miss any negative history because what we are doing here is if the patient has smoking and the patient is giving history of chronic smoking with progressive breathlessness this will be a positive history for you whereas all this is the negative history that you are taking to rule out all the other causes similarly here if the patient has a respiratory cause then all this is the negative history that you are taking to rule out the cardiac cause