Medical Pathology: Disease Factors & Specific Conditions
Factors Contributing to Disease
Immunologic Agents
Immunologic agents protect the host against various injurious agents but may also turn lethal and cause cell injury. Examples include:
- Hypersensitivity reactions
- Anaphylactic reactions
- Autoimmune diseases
Nutritional Derangements
A deficiency or an excess of nutrients may result in nutritional imbalances.
Nutritional deficiency diseases may be due to an overall deficiency of nutrients (e.g., starvation), of protein-calorie (e.g., marasmus, kwashiorkor), of minerals (e.g., anemia), or of trace elements.
Nutritional excess is a problem of affluent societies, resulting in obesity, atherosclerosis, heart disease, and hypertension.
Aging
Cellular aging or senescence leads to impaired ability of cells to undergo replication and repair, ultimately leading to cell death and culminating in the death of the individual.
Psychogenic Diseases
Psychogenic diseases are conditions influenced by psychological factors.
Iatrogenic Factors
Iatrogenic factors refer to diseases and deaths attributed to medical intervention (owing to a physician). Examples include the occurrence of disease or death due to error in judgment by the physician and untoward effects of administered therapy (e.g., drugs, radiation).
Idiopathic Diseases
Idiopathic diseases are conditions of unknown cause.
Pseudotumors
Definition: An enlargement that resembles a tumor that may result from inflammation, accumulation of fluid, or other causes, and may or may not regress spontaneously.
A pseudotumor is a pathological lesion that grossly or clinically resembles a genuine tumor, but its nature is non-neoplastic. Biologically, all pseudotumors are benign.
Pathological Changes in Pseudotumors
- Cysts
- Inflammation
- Developmental Anomalies
- Hyperplasia
Epidermoid Cyst: A Type of Pseudotumor
An epidermoid cyst is a cavity that arises from the dilatation of a pre-existing structure and is generally lined by epithelium.
These are a common type of keratinous cyst (cysts filled with keratin). They are situated in the dermis or subcutaneous tissue and appear spontaneously. The cyst is filled with horny keratinous material. A foreign body reaction may occur when the wall of the cyst ruptures, thus forming a keratin-induced granuloma.
Epidermoid cysts are often induced by epidermis being transplanted into deeper skin layers from trauma.
Inflammatory Pseudotumors
These are a group of inflammatory enlargements, especially in the orbit of the eye, which clinically look like tumors but surgical exploration and pathologic examination fail to reveal any evidence of neoplasm.
They are composed of granulation tissue with leukocyte infiltration.
Pseudotumor Cerebri
Pseudotumor cerebri is characterized by idiopathic cerebral edema and raised intracranial pressure without neurological signs, except for occasional sixth cranial nerve palsy.
Bacterial Pneumonias
Bacterial infection of the lung parenchyma is the most common cause of pneumonia or consolidation of one or both lungs. Two types of acute bacterial pneumonias are distinguished:
- Lobar pneumonia
- Broncho- (lobular-) pneumonia
Each type has distinct etiologic agents and morphologic changes. Another type, confluent pneumonia, combines the features of both lobar and bronchopneumonia.
Lobar Pneumonia
Lobar pneumonia is an acute bacterial infection affecting a part of a lobe, an entire lobe, or even two lobes of one or both lungs.
Etiology of Lobar Pneumonia
- Pneumococcal pneumonia: Caused by Streptococcus pneumoniae.
- Staphylococcal pneumonia: Staphylococcus aureus causes pneumonia by hematogenous spread of infection.
- Gram-negative aerobic bacteria: Less common causes include Haemophilus influenzae, Klebsiella pneumoniae (Friedländer’s bacillus), Pseudomonas, Proteus, and Escherichia coli.
Complications of Lobar Pneumonia
- Organization: In about 3% of cases, resolution of the exudate does not occur; instead, it undergoes organization. This involves the ingrowth of fibroblasts from the alveolar septa, resulting in fibrosed, tough, airless, leathery lung tissue. This type of post-pneumonic fibrosis is called carnification.
- Pleural effusion: Inflammation of the pleura with fluid accumulation.
- Empyema: Encysted pus in the pleural cavity, often a complication of lobar pneumonia.
- Lung abscess: Especially when there is secondary infection by other organisms.
- Metastatic infection: Occasionally, infection in the lungs and pleural cavity in lobar pneumonia may extend into the pericardium and heart, causing purulent pericarditis, bacterial endocarditis, myocarditis, or brain abscess.
Clinical Features of Lobar Pneumonia
- Shaking and chills
- Fever, malaise with pleuritic chest pain, dyspnea, and cough with expectoration (which may be mucoid, purulent, or even bloody)
- Tachycardia, tachypnea, and sometimes cyanosis if the patient is severely hypoxemic
Bronchopneumonia (Lobular Pneumonia)
Bronchopneumonia, or lobular pneumonia, is an infection of the terminal bronchioles that extends into the surrounding alveoli, resulting in patchy consolidation of the lung.
Etiology of Bronchopneumonia
- Staphylococci
- Streptococci
- Pneumococci
- Klebsiella pneumoniae
- Haemophilus influenzae
- Gram-negative bacilli like Pseudomonas and coliform bacteria
Complication of Bronchopneumonia
Bronchiectasis
Clinical Features of Bronchopneumonia
Patients with bronchopneumonia are generally infants or elderly individuals. There may be a history of preceding bedridden illness, chronic debility, aspiration of gastric contents, or upper respiratory infection.
Inflammations of the Larynx
Inflammatory Conditions of the Larynx
Acute Laryngitis
Acute laryngitis may occur as part of an upper or lower respiratory tract infection. Atmospheric pollutants like cigarette smoke, exhaust fumes, industrial, and domestic smoke, etc., predispose the larynx to acute bacterial and viral infections. Streptococci and H. influenzae cause acute epiglottitis, which may be life-threatening. Acute laryngitis may also occur in other illnesses like typhoid, measles, and influenza. Acute pseudomembranous (diphtheritic) laryngitis occurs due to infection with C. diphtheriae.
Chronic Laryngitis
Chronic laryngitis may result from repeated attacks of acute inflammation, excessive smoking, chronic alcoholism, or vocal abuse. The surface is granular due to swollen mucous glands. Extensive squamous metaplasia may occur due to heavy smoking, chronic bronchitis, and atmospheric pollution.
Tuberculous Laryngitis
Tuberculous laryngitis occurs secondary to pulmonary tuberculosis. Typical caseating tubercles are present on the surface of the larynx.
Acute Edema of the Larynx
This hazardous condition is an acute inflammatory state causing swelling of the larynx that may lead to airway obstruction and death by suffocation. Acute laryngeal edema may occur due to trauma, inhalation of irritants, drinking hot fluids, or may be infective in origin.