In many patients, symptoms are present for a considerable time before diagnosis. The most common clinical features of IPF include the following:

- Age over 50 years

- Dry, non-productive cough on exertion

- Progressive exertional dyspnea (shortness of breath with exercise)

- Dry, inspiratory bibasilar "velcro-like" crackles on auscultation (a crackling sound in the lungs during inhalation similar to Velcro being torn apart slowly, heard with a stethoscope).

- Clubbing of the digits, a disfigurement of the finger tips or toes (see image)

- Abnormal pulmonary function test results, with evidence of restriction and impaired gas exchange.

Some of these features are due to chronic hypoxemia (oxygen deficiency in the blood), are not specific for IPF, and can occur in other pulmonary disorders. IPF should be considered in all patients with unexplained chronic exertional dyspnea who present with cough, inspiratory bibasilar crackles, or finger clubbing.

Assessment of "velcro" crackles on lung auscultation is a practical way to improve the earlier diagnosis of IPF. Fine crackles are easily recognized by clinicians and are characteristic of IPF.

If bilateral fine crackles are present throughout the inspiratory time and are persisting after several deep breaths, and if remaining present on several occasions several weeks apart in a subject aged ≥60 years, this should raise the suspicion of IPF and lead to consideration of an HRCT scan of the chest which is more sensitive than a chest X-ray. As crackles are not specific for IPF, they must prompt a thorough diagnostic process.

In disorders that are intrinsic to the lung parenchyma, the underlying process is usually pulmonary fibrosis (scarring of the lung). As the disease progresses, the normal lung tissue is gradually replaced by scar tissue interspersed with pockets of air. This can lead to parts of the lung having a honeycomb-like appearance.

Idiopathic pulmonary fibrosis (IPF) is a chronic irreversible and ultimately fatal disease characterized by a progressive decline in lung function. American Thoracic Society/European Respiratory Society International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. This official statement of the American Thoracic Society (ATS), and the European Respiratory Society (ERS) was approved by the ATS board of directors, June 2013 and by the ERS Steering Committee, March 2013. "Am Respir Crit Care Med." 188 (6): 733–748. September 15, 2013. The term pulmonary fibrosis means scarring of lung tissue and is the cause of worsening dyspnea (shortness of breath). Fibrosis is usually associated with a poor prognosis.

IPF belongs to a large group of more than 200 lung diseases known as interstitial lung diseases (ILDs), characterized by the involvement of lung interstitium. The interstitium, the tissue between the air sacs in the lung, is the primary site of injury in ILDs. However, these disorders frequently affect not only the interstitium, but also the airspaces, peripheral airways, and vessels. Lung tissue from people with IPF shows a characteristic histopathologic pattern known as usual interstitial pneumonia (UIP). UIP is therefore the pathologic counterpart of IPF. The term 'idiopathic' is used because the cause of pulmonary fibrosis is still unknown. IPF usually occurs in adults of between 50 and 70 years of age, particularly those with a history of cigarette smoking, and affects more men than women. The diagnosis of IPF requires exclusion of other known causes of ILDs and the presence of a typical radiological pattern identified through high resolution computed tomography (HRCT). In the right clinical setting, it is possible to make the diagnosis of IPF by HRCT alone, obviating the need for surgical lung biopsy.

Treatment to slow down the progression of the disease may include nintedanib or pirfenidone.

Restrictive lung diseases (or restrictive ventilatory defects) are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.

Extrapulmonary restriction is a type of restrictive lung disease, indicated by decreased alveolar ventilation with accompanying hypercapnia. It is characterized as an inhibition to the drive to breathe, or an ineffective restoration of the drive to breathe.

Extrapulmonary restriction can be caused by central and peripheral nervous system dysfunctions, over-sedation, or trauma (such as a broken rib).

Onset of symptoms is often gradual, but in necrotizing staphylococcal or gram-negative bacillary pneumonias patients can be acutely ill. Cough, fever with shivering, and night sweats are often present. Cough can be productive of foul smelling purulent mucus (≈70%) or less frequently with blood in one third of cases). Affected individuals may also complain of chest pain, shortness of breath, lethargy and other features of chronic illness.

Those with a lung abscess are generally cachectic at presentation. Finger clubbing is present in one third of patients. Dental decay is common especially in alcoholics and children. On examination of the chest there will be features of consolidation such as localized dullness on percussion and bronchial breath sounds.

Rare nowadays but include spread of infection to other lung segments, bronchiectasis, empyema, and bacteremia with metastatic infection such as brain abscess.

Airway obstruction may cause obstructive pneumonitis or post-obstructive pneumonitis.

Causes of upper airway obstruction include foreign body aspiration, blunt laryngotracheal trauma, penetrating laryngotracheal trauma, tonsillar hypertrophy, paralysis of the vocal cord or vocal fold, acute laryngotracheitis such as viral croup, bacterial tracheitis, epiglottitis, peritonsillar abscess, pertussis, retropharyngeal abscess, spasmodic croup. In basic and advanced life support airway obstructions are often referred to as "A-problems". Management of airways relies on both minimal-invasive and invasive techniques.

Usually the atypical causes also involve atypical symptoms:

- No response to common antibiotics such as sulfonamide and beta-lactams like penicillin.

- No signs and symptoms of lobar consolidation, meaning that the infection is restricted to small areas, rather than involving a whole lobe. As the disease progresses, however, the look can tend to lobar pneumonia.

- Absence of leukocytosis.

- Extrapulmonary symptoms, related to the causing organism.

- Moderate amount of sputum, or no sputum at all (i.e. non-productive).

- Lack of alveolar exudate.

- Despite general symptoms and problems with the upper respiratory tract (such as high fever, headache, a dry irritating cough followed later by a productive cough with radiographs showing consolidation), there are in general few physical signs. The patient looks better than the symptoms suggest.

Chest radiographs (X-ray photographs) often show a pulmonary infection before physical signs of atypical pneumonia are observable at all.

This is occult pneumonia. In general, occult pneumonia is rather often present in patients with pneumonia and can also be caused by "Streptococcus pneumoniae", as the decrease of occult pneumonia after vaccination of children with a pneumococcal vaccine suggests.

Infiltration commonly begins in the perihilar region (where the bronchus begins) and spreads in a wedge- or fan-shaped fashion toward the periphery of the lung field. The process most often involves the lower lobe, but may affect any lobe or combination of lobes.

Tuberculosis may infect any part of the body, but most commonly occurs in the lungs (known as pulmonary tuberculosis). Extrapulmonary TB occurs when tuberculosis develops outside of the lungs, although extrapulmonary TB may coexist with pulmonary TB.

General signs and symptoms include fever, chills, night sweats, loss of appetite, weight loss, and fatigue. Significant nail clubbing may also occur.

Patients with miliary tuberculosis often experience non-specific signs, such as coughing and enlarged lymph nodes. Miliary tuberculosis can also present with enlarged liver (40% of cases), enlarged spleen (15%), inflammation of the pancreas (<5%), and multiple organ dysfunction with adrenal insufficiency (adrenal glands do not produce enough steroid hormones to regulate organ function). Miliary tuberculosis may also present with unilateral or bilateral pneumothorax rarely. Stool may also be diarrheal in nature and appearance.

Other symptoms include fever, hypercalcemia, chorodial tubercles and cutaneous lesions.

Firstly, many patients can experience a fever lasting several weeks with daily spikes in morning temperatures.

Secondly, hypercalcemia prevails in 16 to 51% of tuberculosis cases. It is thought that hypercalcemia occurs as a response to increased macrophage activity in the body. Such that, 1,25 dihydroxycholecalciferol (also referred to as calcitriol) improves the ability of macrophages to kill bacteria; however, higher levels of calcitriol lead to higher calcium levels, and thus hypercalcemia in some cases. Thus, hypercalcemia proves to be an important symptom of miliary tuberculosis.

Thirdly, chorodial tubercules, pale lesions on the optic nerve, typically indicate miliary tuberculosis in children. These lesions may occur in one eye or both; the number of lesions varies between patients. Chorodial tubercules may serve as important symptoms of miliary tuberculosis, since their presence can often confirm suspected diagnosis.

Lastly, between 10 and 30% of adults, and 20–40% of children with miliary tuberculosis have tuberculosis meningitis. This relationship results from myobacteria from miliary tuberculosis spreading to the brain and the subarachnoid space; as a result, leading to tuberculosis meningitis.

The risk factors for contracting miliary tuberculosis are being in direct contact with a person who has it, living in unsanitary conditions, and having an unhealthy diet. In the U.S., risk factors for contracting the disease include homelessness and HIV/AIDS.

If a tuberculosis infection does become active, it most commonly involves the lungs (in about 90% of cases). Symptoms may include chest pain and a prolonged cough producing sputum. About 25% of people may not have any symptoms (i.e. they remain "asymptomatic"). Occasionally, people may cough up blood in small amounts, and in very rare cases, the infection may erode into the pulmonary artery or a Rasmussen's aneurysm, resulting in massive bleeding. Tuberculosis may become a chronic illness and cause extensive scarring in the upper lobes of the lungs. The upper lung lobes are more frequently affected by tuberculosis than the lower ones. The reason for this difference is not clear. It may be due to either better air flow, or poor lymph drainage within the upper lungs.

If left untreated, miliary tuberculosis is almost always fatal. Although most cases of miliary tuberculosis are treatable, the mortality rate among children with miliary tuberculosis remains 15 to 20% and for adults 25 to 30%. One of the main causes for these high mortality rates includes late detection of disease caused by non-specific symptoms. Non-specific symptoms include: coughing, weight loss, or organ dysfunction. These symptoms may be implicated in numerous disorders, thus delaying diagnosis. Misdiagnosis with tuberculosis meningitis is also a common occurrence when patients are tested for tuberculosis, since the two forms of tuberculosis have high rates of co-occurrence.

A septic embolism can be difficult to identify, as it is often attributed to other disorders or infections of the body. As a result, it may wreak havoc with CT scans. It can also be confused with lymph nodules, considering the similarity in shape and size. However, septic emboli usually lodge in the heart valves, where there are no lymph nodes.

Pneumocystosis is an infection by "Pneumocystis jirovecii"that primarily occurs as a pulmonary infection AIDS patients, with extrapulmonary involvement being uncommon but, if occurring in the skin, presenting most often as nodular growths in the auditory canal.

"M. pneumoniae" infections can be differentiated from other types of pneumonia by the relatively slow progression of symptoms. A positive blood test for cold-hemagglutinins in 50–70% of patients after 10 days of infection (cold-hemagglutinin-test should be used with caution or not at all, since 50% of the tests are false-positive), lack of bacteria in a Gram-stained sputum sample, and a lack of growth on blood agar.

PCR has also been used.

A septic embolism is a type of embolism that is infected with bacteria, resulting in the formation of pus. These may become dangerous if dislodged from their original location. Like other emboli, a septic embolism may be fatal.

One of the common microbes that can lead to widespread dissemination of septic emboli is "Fusobacterium necrophorum", a Gram negative anaerobic bacillus. Fusobacteria are commensal organisms in the oral cavity.

"F. necrophorum" and" F. nucleatum" are the most important among the non-spore forming anaerobic bacilli in causing human infections." F. necroporum" may occasionally cause septicaemia with metastatic abscesses (Lemierre's syndrome).

"Mycoplasma pneumoniae" is spread through respiratory droplet transmission. Once attached to the mucosa of a host organism, "M. pneumoniae" extracts nutrients, grows, and reproduces by binary fission. Attachment sites include the upper and lower respiratory tract, causing pharyngitis, bronchitis, and pneumonia. The infection caused by this bacterium is called atypical pneumonia because of its protracted course and lack of sputum production and wealth of extrapulmonary symptoms. Chronic "Mycoplasma" infections have been implicated in the pathogenesis of rheumatoid arthritis and other rheumatological diseases.

"Mycoplasma" atypical pneumonia can be complicated by Stevens–Johnson syndrome, autoimmune hemolytic anemia, cardiovascular diseases, encephalitis, or Guillain–Barré syndrome.

Mild ascites is hard to notice, but severe ascites leads to abdominal distension. Patients with ascites generally will complain of progressive abdominal heaviness and pressure as well as shortness of breath due to mechanical impingement on the diaphragm.

Ascites is detected on physical examination of the abdomen by visible bulging of the flanks in the reclining patient ("flank bulging"), "shifting dullness" (difference in percussion note in the flanks that shifts when the patient is turned on the side) or in massive ascites with a "fluid thrill" or "fluid wave" (tapping or pushing on one side will generate a wave-like effect through the fluid that can be felt in the opposite side of the abdomen).

Other signs of ascites may be present due to its underlying cause. For instance, in portal hypertension (perhaps due to cirrhosis or fibrosis of the liver) patients may also complain of leg swelling, bruising, gynecomastia, hematemesis, or mental changes due to encephalopathy. Those with ascites due to cancer (peritoneal carcinomatosis) may complain of chronic fatigue or weight loss. Those with ascites due to heart failure may also complain of shortness of breath as well as wheezing and exercise intolerance.

Once considered rare, its occurrence has increased due to AIDS. It is now the third most common opportunistic infection (after extrapulmonary tuberculosis and cryptococcosis) in HIV-positive individuals within the endemic area of Southeast Asia.

Penicilliosis (or penicillosis) is an infection caused by "Penicillium marneffei".

It is a dimorphic fungus.

Ascites is the abnormal buildup of fluid in the abdomen. Technically it is more than 25 mL of fluid in the peritoneal cavity. Symptoms may include increased abdominal size, increased weight, abdominal discomfort, and shortness of breath. Complications can include spontaneous bacterial peritonitis.

In the developed world the most common cause is liver cirrhosis. Other causes include cancer, heart failure, tuberculosis, pancreatitis, and blockage of the hepatic vein. In cirrhosis the underlying mechanism involves high blood pressure in the portal system and dysfunction of blood vessels. Diagnosis is typically based on a examination together with ultrasound or a CT scan. Testing the fluid can help in determining the underlying cause.

Treatment often involves a low salt diet, medication such as diuretics, and draining the fluid. A transjugular intrahepatic portosystemic shunt (TIPS) may be placed but is associated with complications. Effects to treat the underlying cause, such as by a liver transplant may be considered. Of those with cirrhosis, more than half develop ascites in the ten years following diagnosis. Once ascites has developed in this group, average life expectancy is less than three years. The term is from the Greek "askítes" meaning "baglike".

Small-cell carcinoma of the lung usually presents in the central airways and infiltrates the submucosa leading to narrowing of bronchial airways. Common symptoms include cough, dyspnea, weight loss, and debility. Over 70% of patients with small-cell carcinoma present with metastatic disease; common sites include liver, adrenals, bone, and brain.

Due to its high grade neuroendocrine nature, small-cell carcinomas can produce ectopic hormones, including adrenocorticotropic hormone (ACTH) and anti-diuretic hormone (ADH). Ectopic production of large amounts of ADH leads to syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH).

Lambert-Eaton myasthenic syndrome (LEMS) is a well-known paraneoplastic condition linked to small-cell carcinoma.