A 53-year-old man comes to the emergency department due to severe heartburn and difficulty swallowing for the last few weeks. He has had mild to moderate heartburn for several years and has tried weight loss, elevation of the head of his bed while sleeping, and several months of proton pump inhibitor therapy. Other medical conditions include hypertension and hypothyroidism. Temperature is 36.7 C (98.1 F), blood pressure is 130/80 mm Hg, pulse is 78/min, and respirations are 16/min. BMI is 25 kg/m2. Physical examination is unremarkable. An upper gastrointestinal endoscopy is performed, and esophageal biopsy shows columnar epithelium with interspersed goblet cells. A similar adaptive response is most likely to be seen in which of the following scenarios?
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The esophagus is normally lined by nonkeratinized, stratified squamous epithelium. However, chronic exposure to acidic stomach contents can damage the epithelial surface and result in the release of cytokines and growth factors that cause esophageal stem cells to differentiate into an alternate epithelial cell type (columnar epithelium with goblet cells) better suited for an acidic environment. The substitution of one differentiated epithelial cell type for another in response to adverse environmental conditions is called metaplasia.
Metaplasia is also seen in the trachea and bronchi of chronic cigarette smokers; there, the irritative effect of smoke leads to replacement of normal ciliated columnar cells with heartier stratified squamous epithelium. Although this cellular adaptation reduces epithelial injury, it also eliminates the cell types that contain cilia and produce mucus, which increases the risk for respiratory infection.
Metaplasia is a reversible condition, but continued environmental stress can lead to malignant transformation (metaplasia → dysplasia → invasive cancer). For instance, the metaplasia seen in the distal esophagus in response to chronic acid exposure (Barrett esophagus) is associated with a risk for malignant transformation into esophageal adenocarcinoma.
(Choice B) Hyperplasia refers to an increase in the number of cells within a tissue due to hormones or growth factors. Psoriasis is characterized by epidermal hyperplasia that results in acanthosis (ie, epidermal thickening).
(Choice C) Neoplasia refers to uncontrolled clonal cellular growth; it can be malignant (ie, capable of invading and metastasizing) or benign. A firm, fixed breast mass is concerning for a malignant neoplasm, such as invasive ductal carcinoma, which is characterized by infiltrative neoplastic epithelial cells.
(Choice D) Dysplasia (ie, disordered growth) is often characterized by abnormal cellular architecture and cytologic atypia. Irregular moles (eg, dysplastic nevi) likely contain dysplastic melanocytes.
(Choice E) Hypertrophy is an increase in the size, but not the number, of cells. Left ventricular hypertrophy can occur with aortic stenosis due to the higher systolic pressures necessitating increased myocardial effort.
(Choice F) Atrophy is a reduction in cell size and number. It can occur in skeletal muscles secondary to disuse, such as a period of immobility (eg, patient with a mobility disability).
Educational objective:
Metaplasia is the substitution of one differentiated cell type for another in response to an adverse environmental stimulus. It is often seen in the bronchi of chronic cigarette smokers (ciliated columnar epithelium replaced by stratified squamous epithelium) and in the distal esophagus of patients with chronic gastroesophageal reflux (stratified squamous epithelium replaced by intestinal columnar epithelium).