Lactase Deficiency (Acquired)

Overview

Plain-Language Overview

Lactase deficiency is a condition where the small intestine produces less of the enzyme lactase, which is needed to digest lactose, the sugar found in milk and dairy products. When lactase levels are low, lactose is not properly broken down and can cause symptoms like bloating, diarrhea, and stomach pain after consuming dairy. This condition often develops in adulthood and is more common in certain ethnic groups. It is not the same as a milk allergy, which involves the immune system. People with lactase deficiency may need to adjust their diet to manage symptoms.

Clinical Definition

Acquired lactase deficiency, also known as secondary lactase deficiency, is characterized by a reduction in lactase enzyme activity in the brush border of the small intestinal mucosa, leading to impaired hydrolysis of lactose into glucose and galactose. This deficiency results in malabsorption of lactose, causing osmotic diarrhea, abdominal pain, bloating, and flatulence upon ingestion of lactose-containing foods. It typically occurs after an insult to the small intestine such as infectious gastroenteritis, celiac disease, Crohn's disease, or other causes of mucosal injury. The condition differs from primary lactase deficiency, which is genetically determined and progressive. Diagnosis involves clinical suspicion supported by tests demonstrating lactose malabsorption. The pathophysiology involves decreased expression or activity of the lactase-phlorizin hydrolase enzyme complex. Symptoms arise due to fermentation of unabsorbed lactose by colonic bacteria producing gas and short-chain fatty acids. Management focuses on treating the underlying cause and dietary modification to reduce lactose intake.

Inciting Event

Acute or chronic small intestinal mucosal injury from infections, inflammation, or ischemia.
Episodes of gastroenteritis caused by viral or bacterial pathogens.
Onset or exacerbation of inflammatory bowel disease involving the small intestine.

Latency Period

Symptoms typically develop within days to weeks after the inciting intestinal injury.

Diagnostic Delay

Symptoms may be attributed to other causes such as irritable bowel syndrome or food intolerance.
Lack of awareness that lactase deficiency can be acquired rather than only genetic.
Overlap of symptoms with underlying gastrointestinal diseases complicates diagnosis.

Clinical Presentation

Signs & Symptoms

Postprandial abdominal cramps and bloating after lactose-containing meals.
Watery diarrhea due to osmotic effect of unabsorbed lactose.
Excessive flatulence and borborygmi from bacterial fermentation of lactose.
Nausea and occasional vomiting may occur.

History of Present Illness

Postprandial abdominal bloating, cramping, and diarrhea occurring after ingestion of lactose-containing foods.
Onset of symptoms following recent gastrointestinal infection or flare of inflammatory bowel disease.
Symptoms include flatulence and sometimes nausea without systemic signs of infection.

Past Medical History

History of gastroenteritis or small intestinal infections.
Chronic inflammatory bowel disease such as Crohn's disease.
Previous diagnosis of celiac disease or other causes of small intestinal mucosal damage.

Family History

Usually no significant family history as acquired lactase deficiency is not inherited.
Family history may reveal primary lactase deficiency in some cases, which is genetically determined.

Physical Exam Findings

Abdominal distension may be observed due to gas accumulation.
Bowel sounds are typically normal or hyperactive.
No signs of peritoneal irritation or abdominal tenderness.

Diagnostic Workup

Diagnostic Criteria

Diagnosis of acquired lactase deficiency is based on clinical history of symptoms such as diarrhea, bloating, and abdominal pain following lactose ingestion, combined with objective evidence of lactose malabsorption. This can be confirmed by a positive lactose hydrogen breath test showing increased hydrogen production after lactose challenge, or by a lactose tolerance test demonstrating a failure to increase blood glucose levels after lactose ingestion. Small bowel biopsy showing decreased lactase activity may be used in uncertain cases. Exclusion of other causes of malabsorption and correlation with an underlying intestinal pathology support the diagnosis.

Pathophysiology

Key Mechanisms

Acquired lactase deficiency results from decreased expression of the lactase enzyme on the brush border of the small intestinal mucosa.
Reduced lactase activity leads to impaired hydrolysis of lactose into glucose and galactose, causing lactose malabsorption.
Unabsorbed lactose is fermented by colonic bacteria, producing short-chain fatty acids and gases that cause symptoms.

Involvement	Details
Organs	Small intestine is the organ responsible for lactose digestion and nutrient absorption.
Tissues	Intestinal mucosa contains the brush border where lactase is expressed and lactose digestion occurs.
Cells	Enterocytes in the small intestine produce lactase enzyme on their brush border membrane.
Cells	Goblet cells secrete mucus that protects the intestinal lining but do not produce lactase.
Chemical Mediators	Lactase is the key enzyme that hydrolyzes lactose into glucose and galactose for absorption.

Treatment

Pharmacological Treatments

Lactase enzyme supplements
- Mechanism: Provide exogenous lactase to digest lactose in the intestine
- Side effects: bloating, abdominal cramps, diarrhea

Non-pharmacological Treatments

Avoidance of lactose-containing foods such as milk and dairy products.
Use of lactose-free dairy alternatives like almond or soy milk.
Gradual introduction of small amounts of lactose to improve tolerance.

Prevention

Pharmacological Prevention

Oral lactase enzyme supplements taken before lactose ingestion to improve digestion.

Non-pharmacological Prevention

Avoidance of lactose-containing foods such as milk and soft cheeses.
Use of lactose-free dairy products.
Gradual introduction of small amounts of lactose to improve tolerance.

Outcome & Complications

Complications

Nutritional deficiencies such as calcium and vitamin D deficiency due to dairy avoidance.
Weight loss and malnutrition in severe cases.
Dehydration from chronic diarrhea.

Short-term Sequelae	Long-term Sequelae
Acute diarrhea and abdominal discomfort after lactose ingestion. Electrolyte imbalance secondary to diarrhea.	Chronic calcium deficiency leading to osteopenia or osteoporosis. Persistent malnutrition if dairy products are not adequately replaced.

Differential Diagnoses

Lactase Deficiency (Acquired) versus Celiac Disease

Lactase Deficiency (Acquired)	Celiac Disease
Normal small bowel biopsy without villous atrophy.	Presence of villous atrophy on small bowel biopsy and positive anti-tissue transglutaminase (tTG) antibodies.
Symptoms limited to lactose intolerance without systemic malabsorption signs.	Symptoms include weight loss, iron deficiency anemia, and steatorrhea beyond lactose intolerance.
Symptom relief primarily with lactose avoidance rather than gluten restriction.	Improvement with a strict gluten-free diet rather than lactose restriction.

Lactase Deficiency (Acquired) versus Irritable Bowel Syndrome (IBS)

Lactase Deficiency (Acquired)	Irritable Bowel Syndrome (IBS)
Onset of diarrhea and bloating specifically after lactose-containing food ingestion.	Presence of abdominal pain relieved by defecation and associated with altered bowel habits without malabsorption.
Positive lactose hydrogen breath test indicating lactose malabsorption.	Normal lactose hydrogen breath test and absence of osmotic diarrhea.
Improvement of symptoms with lactose-free diet.	Symptoms often triggered by stress or certain foods but not specifically by lactose ingestion.

Lactase Deficiency (Acquired) versus Small Intestinal Bacterial Overgrowth (SIBO)

Lactase Deficiency (Acquired)	Small Intestinal Bacterial Overgrowth (SIBO)
Positive lactose hydrogen breath test with symptoms specifically after lactose ingestion.	Positive glucose hydrogen breath test with early hydrogen peak indicating bacterial overgrowth.
Symptoms primarily triggered by lactose-containing foods.	Symptoms include bloating, flatulence, and diarrhea not exclusively related to lactose ingestion.
Improvement with lactose-free diet rather than antibiotics.	Response to antibiotic therapy rather than lactose restriction.