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The primary function of the respiratory system is to provide adequate and adaptive gas exchange with a supply of oxygen to the body and removal of carbon dioxide. Illness can disturb this function by affecting 1 or more of the following: the central control of breathing, the respiratory pump comprising the chest cage and respiratory muscles, the small and large airways, and the pulmonary parenchyma. Nonrespiratory functions of the lung include production and regulation of surfactant, defense against infections, effective mucociliary clearance, participation in water and fluid balances, filtering of blood cells and emboli, and elimination of volatile substances.
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Respiratory illness in children usually presents with clinical symptoms and signs that offer important diagnostic information. A clinical examination of the respiratory system should including inspection, palpation/percussion, and auscultation.
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The thoracic cage is vital for the efficient bellows action of the respiratory pump. Congenital or acquired malformations of the chest wall can, therefore, impact considerably on lung volume and function. Congenital anomalies involve the sternum with concavity (pectus excavatum, see Fig. 498-1) or protrusion (pectus carinatum), the spine (eg, scoliosis, kyphosis), or the ribs themselves, sometimes in combination with an overall small thoracic cage (eg, Jeune syndrome or cerebrocostomandibular syndrome).
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Acquired deformations of the chest wall can be secondary to neuromuscular weakness (eg, flattening of the chest in children with spinal muscular atrophy) or reflect underlying chronic respiratory diseases. The Harrison sulcus, for example, is a groove along the lower ribs corresponding to the attachment of the diaphragm that develops after prolonged increase in the work of breathing. A secondary pectus excavatum might develop after longstanding upper airway obstruction. Chronic hyperinflation (eg, in asthma or cystic fibrosis) can lead to a barrel chest with increase of the anterior-posterior diameter of the thorax.
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The respiratory rate (breaths per minute) is essential for assessing the respiratory function of children. Normal ranges are dependent on age, weight, body temperature, wakefulness, and the activity level of the child. The respiratory rate is counted by observing chest and abdominal movements or by listening to breaths with a stethoscope. The respiratory rate can be calculated by counting breaths for 15 or 30 seconds and multiplying the resulting number by 4 or 2, respectively. Table 498-1 shows reference values for afebrile children from birth to 18 years of age.
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In young febrile children, tachypnea, that is, a respiratory rate faster than normal, is an important predictive sign for pneumonia when the respiratory rate per minute exceeds 59 in those younger than 6 months of age, 52 in those between 6 and 11 months, and 42 in those between 1 and 2 years.
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Abnormal breathing rates are not seen only in respiratory conditions. Cardiac disorders, metabolic acidosis, and psychogenic conditions also lead to tachypnea, whereas bradypnea (abnormally low rate) can indicate raised intracranial pressure.
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Apart from the respiratory rate, it is important to recognize pathologic breathing patterns. The most relevant in pediatrics include the following:
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Apnea (complete cessation of breathing due to central or obstructive causes)
Hypopnea (shallow breathing)
Hypo- and hyperventilation (decreased or increased alveolar ventilation leading to hypercapnea or hypocapnea, respectively)
Kussmaul breathing (deep, regular sighing respiration due to metabolic acidosis)
Cheyne-Stokes breathing (repetitive pattern of increasing then decreasing tidal volumes followed by an apnea, indicative for brain injury)
Periodic breathing (clusters of breaths interrupted by apneas lasting as long as 10 seconds, a common finding in neonates and preterm babies)
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DYSPNEA AND WORK OF BREATHING
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Dyspnea is the subjective feeling of breathlessness and can be accompanied by increased work of breathing. Reasons for increased work of breathing in respiratory illness include not only increased resistance to air flow (eg, in airway obstruction) or decreased pulmonary compliance (eg, in atelectasis and restrictive lung diseases, or marked air trapping), but also restrictive chest wall conditions (eg, in severe thoracic scoliosis).
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Objective signs of increased respiratory effort are a tracheal tug (an indrawing seen at the sternal notch) and intercostal or subcostal recessions; the latter is readily seen in young children, as the chest wall is more compliant.
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Children in respiratory distress also use the accessory respiratory muscles (sternocleidomastoid and scalene muscle, the pectoralis major, trapezius, and abdominal muscles). This effort can lead to “head bobbing” in infants, whereas older children tend to adopt a tripod position (resting of the arms or hands on the knees while bending forward). Nasal flaring also may be observed, especially in infants, and helps to decrease the resistance in the upper airways during inspiration.
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Severe respiratory distress is characterized by seesaw-type movements of the thorax and abdomen; whereas normal inspiration causes the abdominal content to be pushed outward, seesaw breathing is characterized by an inward movement of the abdomen during inspiration.
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Increased work of breathing with asymmetric chest excursion (with possible tracheal deviation from the midline) may occur in a pneumothorax, lung aplasia/hypoplasia, and paralysis of 1 hemidiaphragm.
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Digital clubbing is thickening of the connective tissue of the distal phalanges of toes and fingers with a flattening of the nail bed. While typically found in suppurative lung disorders such as cystic fibrosis, bronchiectasis, chronic empyema, and lung abscesses, digital clubbing also is associated with cardiac diseases, endocarditis, liver diseases, or inflammatory bowel disease. Rarely, clubbing can be idiopathic or familial.
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Clubbing can be demonstrated by Schamroth’s sign: opposing the thumbs or index fingers nail-to-nail creates a diamond-shaped gap in healthy individuals that is obliterated in the presence of digital clubbing. Additionally, the hyponychial angle (angle between the skin fold from which the nail originates and the nail surface) is > 180° in digital clubbing, whereas healthy individuals have an angle of < 180° (Fig. 498-2).
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Several hypotheses are discussed for the development of clubbing, and most involve vascular endothelial growth factor (VEGF). Local overproduction of VEGF and also systemically raised levels of VEGF are thought to lead to increased mesenchymal proliferation of the distal phalanges of fingers and toes. Activated megakaryocytes and thrombocytes may be local sources of VEGF. Megakaryocytes normally are filtered in the pulmonary capillary bed; however, in conditions with intrapulmonary shunts, they can end up in the capillary bed of the phalanges, where they are thought to release VEGF. Generalized hypoxemia also leads to increased levels of VEGF.
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Occasionally, clubbing can be associated with increased periosteal inflammation called hypertrophic osteoarthropathy; typical signs are painful swelling of the wrists, knees, ankles, or elbows.
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Cyanosis refers to bluish or purplish discoloration of skin and mucous membranes caused by an increased proportion of deoxygenated hemoglobin in the circulation. Deoxygenated hemoglobin has a blue hue, whereas oxyhemoglobin has a bright red color. Cyanosis becomes clinically detectable only after considerable hypoxemia: deoxygenated hemoglobin needs to exceed 3 g/dL in arterial blood and 4 to 6 g/dL in venous blood for cyanosis to become apparent. Additionally, the detection of cyanosis also is influenced by skin pigmentation, intensity of light, and the patient’s hemoglobin concentration. Clinical detection of cyanosis is quite unreliable. In polycythemia, for example, cyanosis will easily become apparent at arterial oxygen saturations below 85%, whereas in anemia, the saturation has to fall below 65%.
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Central cyanosis indicates arterial hypoxemia and is always a serious sign. It is best seen by examining the mucous membranes, lips, and tongue. Peripheral cyanosis of fingers and toes can be present without arterial hypoxemia when oxygen extraction in the capillary bed is increased due to sluggish circulation, for example, with cold-induced vasoconstriction or decreased perfusion pressures.
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A reliable method to detect hypoxemia in clinical practice is pulse oximetry, which is sometimes called the fifth vital sign in addition to the 4 classical vital signs of temperature, heart rate, respiratory rate, and blood pressure. Pulse oximetry, however, does have some clinical limitations. Measurements of oxygen saturation (SpO2) rely on the absorption characteristics of oxyhemoglobin and deoxyhemoglobin and the systolic pulsatile wave. During hemodynamic shock and in situations with severely compromised circulation, pulse oximetry may yield inaccurate or failed readings. Pulse oximetry also is unreliable in carbon monoxide intoxication and sickle cell vaso-occlusive crises (false normal or high SpO2), methemoglobinemia (both false low or high SpO2), inherited dyshemoglobinemias, excessive movement, severe anemia, and ambient light interference (false low SpO2 readings).
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Fetal and adult hemoglobin do not differ in regard to their absorption characteristics, which renders pulse oximetry a reliable test in neonates.
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PALPATION AND PERCUSSION
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Palpation of the chest is used to feel for transmitted vibrations and to examine chest excursions during respiration. The air-filled lungs normally dampen all vibrations caused by phonation. In diseases with increased tissue density (eg, caused by pneumonic consolidation), vibrations originating from the vocal cords might become palpable, a phenomenon called vocal fremitus.
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Palpation of the chest wall can also be used to detect loose secretions while the patient coughs or “huffs”—a forced expiration with maximal flow. Palpable secretions are found in patients with cystic fibrosis and can indicate a pulmonary exacerbation.
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To assess chest excursion, the examiner’s hands are positioned on the lateral thorax with the thumbs meeting over the sternum. Normal expansion of the ribcage leads to a “bucket handle movement,” which causes the examiner’s thumbs to move away from the midline.
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Palpation of the chest also includes assessment of the position of the trachea above the suprasternal notch, which should normally adopt a central position.
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Percussion of the lungs plays an important role in detecting pneumothoraces (hyperresonant percussion) or consolidation and pleural effusion (dullness to percussion).
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Chest auscultation and assessment of respiratory sounds are central components of the chest examination. Still, the subjective nature of perceiving and describing respiratory sounds and the confusing nomenclature often limit the value of auscultation. New methods using recording of respiratory sounds and computerized sound analysis might help in the future in standardizing the nomenclature and training.
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Respiratory sounds fall into the broad categories of normal or basic breath sounds and abnormal or adventitious breath sounds. Table 498-2 gives an overview of the types of respiratory sounds, their acoustic characteristics, and their clinical relevance.
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Normal Respiratory Sounds
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Normal (basic) lung sounds can be heard over the chest wall in healthy individuals. The term vesicular has been used previously as a descriptive term but is inaccurate because normal lung sounds do not originate from airflow in the alveolar (vesicular) space. Rather, they are generated in the central to segmental airways, while at the level of the alveolar space, gas movement is facilitated by silent diffusion.
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Lung sounds should always be compared between corresponding lung areas to detect overall or localized change in breath sounds. Reduced breath sounds are caused by either diminished sound generation or decreased sound transmission. Diminished generation of breath sounds typically occurs in conditions with reduced respiratory drive (in uncooperative or sedated patients) or weakness of the respiratory muscles (either due to neuromuscular diseases or tiring during a severe asthma attack) and also in obesity or air trapping. During an acute asthma attack, sound production and transmission both are affected as the airway obstruction leads to reduced flow intensity (ie, sound production) as well as reduced sound transmission due to hyperinflation of the lungs.
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Localized reduction of breath sounds is typical for atelectasis and consolidations in the lung parenchyma or for abnormalities of the pleural space (pneumothorax, empyema, or pleural effusion or fibrotic thickening of the pleura).
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Tracheal sounds are best heard over the suprasternal notch and originate from the turbulent air flow in the central airways. In healthy individuals, they cannot be heard over the lateral chest wall due to dampening by the air-filled lungs. Consolidation of lung tissue surrounding a ventilated bronchus (eg, in pneumonia) facilitates better acoustic conductance, and typical sounds from the central airways (tracheal sounds) can be heard over the chest wall. This phenomenon is then called bronchial breathing and is the acoustic equivalent to an air bronchogram seen on a chest x-ray film.
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Additionally, voice transmission also may be enhanced over areas with consolidated lung tissue. While in healthy individuals speech is perceived only as an incomprehensible mumbling when auscultating the chest wall, compressed and consolidated lung tissue improves transmission. This phenomenon is called bronchophony for normal speech or, in case of whispered sounds, pectoriloquy.
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Abnormal Respiratory Sounds
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Abnormal breath sounds, also known as adventitious sounds, comprise stridor, wheeze, crackles, squeaks, and pleural rub. They are classically divided into musical (continuous; ie, longer) and nonmusical (discontinuous; ie, shorter) sounds.
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Stridor is a musical, high-pitched sound that is in most cases audible without a stethoscope. Inspiratory stridor indicates narrowing of the extrathoracic airways (larynx and proximal trachea) due to croup, laryngomalacia, or vocal cord lesions, whereas expiratory stridor is caused by intrathoracic pathologies such as tracheobronchomalacia or extrinsic compression of the trachea or main bronchi.
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Biphasic stridor indicates fixed lesions and severe obstruction (eg, croup, paralysis of both vocal cords, laryngeal mass or web).
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Wheeze and rhonchi are breath sounds indicating partial airway obstruction. The musical aspect is caused by the periodic sinusoidal waveform, which is less prominent in rhonchi, which have a harsher and more “snoring” character.
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Wheeze is one of the most commonly reported symptoms; however, it can be difficult to recognize, especially for parents but also for health professionals. It is often confused with noisy breathing such as rattles or noisy whistling noises from the upper airways. This confusion can lead to considerable overdiagnosis of asthma, especially in preschool children, and consequent overtreatment.
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Wheezes are mainly expiratory and signify partial airway obstruction in the second to seventh generations of airway branches. To overcome the increased resistance in the obstructed airways, maximal driving pressures are generated, which at one point fail to translate into higher air flow. Consequently, the resulting excess energy causes vibrations of the airway walls, which create the characteristic expiratory wheeze.
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The absence of wheeze does not rule out airway obstruction. For example, wheeze may not be heard in shallow breathing, as the airflow intensity is not strong enough to cause the airways to oscillate. With deep breaths, the wheeze becomes audible. However, it is important to note that very forceful expirations can cause wheeze even in healthy individuals. On the other hand, airway obstruction may be so severe that the resulting decreased flow is insufficient to cause any sounds. This phenomenon is called a silent chest and is characteristic of severe, life-threatening asthma attacks or upper airway obstruction.
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Wheeze caused by airway obstruction can be disseminated throughout the lung, as in asthma, or localized, for example due to mucous plugs, bronchomalacia, or a foreign body. Failure to recognize a localized wheeze can lead to an erroneous diagnosis of asthma. Consequently, this might result in unnecessary and especially ineffective treatment, and some patients might even be misdiagnosed with difficult-to-treat asthma.
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Rhonchi are “snore-like” musical sounds of lower frequency than wheeze, and they disappear or change with coughing. They are generated by secretions in the airways and increased airway instability and are typical for asthma or bronchitis.
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Crackles are nonmusical (discontinuous), mostly inspiratory sounds that are subcategorized into fine and course crackles. Fine crackles are most likely due to sudden opening of small airways during inspiration and are heard predominately late during inspiration. They are typical for pediatric interstitial lung diseases in which small airways collapse due to increased elastic recoil forces, edema, or inflammation, as, for example, in acute bronchiolitis.
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Course crackles are louder with a lower frequency and occur during early to mid-inspiration but also in expiration. Course crackles are attributed to the movement of secretions in bronchi and bronchioles. Another mechanism is intermittent opening of airways as pockets of air pass through. Crackles can be present in bronchiectasis, cystic fibrosis, and the early stages of pneumonia (changing to more end-inspiratory fine crackles with further progression of the disease). Course crackles with long duration during inspiration can be a sign of congestive cardiac failure. Transmitted sounds from the pharynx in patients with swallowing difficulties and constant pooling of oral secretions can resemble course crackles. They are loud, have a snoring character, and disappear after suctioning or swallowing.
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Some respiratory sounds are detectable without a stethoscope and are often referred to as noisy breathing. These sounds include snoring, rattling, snuffling, and grunting.
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Snoring is predominately inspiratory and caused by obstruction in the oropharynx due to adenotonsillar hypertrophy, increased instability of the upper airways (neuromuscular diseases, obesity), or craniofacial disorders. Rattles, which can be confused with wheeze when taking a history, are lower and harsher than a wheeze, present in inspiration and expiration, and often associated with palpable chest wall vibrations. They most likely are caused by increased secretions in the central and extrathoracic airways moving alongside with the normal airflow and will clear with coughing. Snuffling refers to nasal sounds only.
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Grunting is an important sign of respiratory distress in neonates and small infants. In older children, grunting is mainly associated with pneumonia. It is generated by short closure of the glottis during expiration, which creates the characteristic grunt. It is thought to generate a positive end-expiratory pressure preventing alveolar collapse.
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Cough is the most common symptom of respiratory disease and a frequent cause for seeking medical attention. In most cases, cough is harmless and self-limiting and a normal physiologic airway defense mechanism.
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Coughing is a complex process; subepithelial mechanoreceptors in the airways are triggered by a multitude of stimuli (dust, chemicals, inflammation, cold temperature, or airway distortion), initiating the cough reflex. After a deep inspiration, the initial forceful expiration is briefly halted by glottic closure, and explosive exhalation follows opening of the vocal cords and closing of the nasopharynx with the soft palate.
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Cerebral venous blood flow may be reduced by the high intrathoracic pressures generated by coughing, causing conjunctival hemorrhage, sparse petechial lesions on the face, and headaches. Paroxysmal coughing (bouts of coughing that cannot be stopped) is typical for pertussis infection or cystic fibrosis and sometimes causes vomiting. Additional complications such as air-leak or rib fractures are rare.
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Cough, especially when chronic, poses a considerable health burden for patients and families as it affects quality of life and causes considerable parental concern. The definition of chronic cough still differs among national guidelines and varies between 4 and 8 weeks; however, recent data suggest that using a 4-week cut off for seeking advice improves the outcome of children with chronic cough. A structured diagnostic approach is shown in Figure 498-3.
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Not all children with chronic cough need further investigations or therapy. Dry cough in otherwise healthy children is harmless in most cases, even if persisting for weeks, and “watchful waiting” might be appropriate. However, it is important to exclude any alarm signs or “pointers” in clinical history and examination. Additionally, it is often helpful to actually listen to the patient coughing either during the consultation or on a recording provided by the caregivers. Symptoms such as productive, wet cough, chest pain, hemoptysis, cyanosis, dyspnea at rest, and reduced activity levels equally point toward an underlying pathology. Cough associated with systemic signs such as failure to thrive or recurrent fever as well as a history of neurodevelopmental abnormalities, cardiac diseases, or immunodeficiency should also be investigated further. Respiratory diseases associated with chronic cough are summarized in Table 498-3.
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Hemoptysis is a rare symptom in children. Young children are more likely to swallow blood emanating from the lungs, and subsequent vomiting can be mistaken for gastrointestinal bleeding. Additionally, pulmonary hemorrhage does not always manifest with hemoptysis and may present with nonspecific symptoms such as cough, dyspnea, or wheeze or extrapulmonary symptoms of anemia.
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The causes of pulmonary hemorrhage can be divided into focal (localized) bleeding and diffuse bleeding. Focal hemorrhage usually originates from hypertrophied bronchial arteries and can be due to cystic fibrosis or other causes of bronchiectasis, or tuberculosis. Rarer causes include hemangiomas, arteriovenous fistulas, or tumors.
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Causes of diffuse hemorrhage are coagulation disorders or cardiac diseases that lead to pulmonary congestion (cardiac failure, left-sided obstruction, or left-to-right shunt), isolated pulmonary and systemic vasculitis (granulomatosis with polyangiitis, previously known as Wegener disease, Henoch-Schönlein purpura, Churg-Strauss syndrome, or microscopic polyangiitis), and diseases affecting the alveoli (in isolation [eg, idiopathic pulmonary hemosiderosis] or as part of a systemic disease [eg, Goodpasture syndrome]). Factitious and induced origins of hemoptysis also need consideration.
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