Lactose intolerance overview

# Overview
Lactose intolerance is the term used to describe a decline in the level of lactase, an enzyme needed for proper metabolization of lactose (a sugar that is a constituent of milk and other dairy products), in human beings.

# Historical Perspective
Lactose intolerance first discovered by Hippocrate, ancient Greek physician 2500 years ago. In 1906, Pimmer discovered lactase enzyme in the intestine of infant dogs, pigs, and rats. The association between ethnic and lactose intolerance was discovered in 1966 by Bayless and Rosensweig. In1978, breath hydrogen test was used by Levitt, to diagnose lactose intolerance.

# Classification
There is no established system for the classification of lactose intolerance. Lactose intolerance may be classified according to its causes into 2 groups: primary lactose malabsorption and secondary lactose malabsorption. Primary lactose malabsorption may be classified into 3 subtypes: acquired primary lactase deficiency, congenital lactase deficiency and developmental lactase deficiency. Secondary lactose malabsorption occurs as a result of the underlying intestinal diseases such as small intestinal bacterial overgrowth, small intestinal infection such as giardiasis and small intestinalinflammation.

# Pathophysiology
It is thought that lactose intolerance is the result of lactose malabsorption that it is caused by low level of small intestinal lactase. Lactose is metabolized by intestinal lactase to galactose and glucose in villous enterocytes. In colon, unabsorbed lactose is converted to hydrogen gas and short chain fatty acids such as acetate, butyrate and propionate by intestinal bacteria and creates symtoms of lactose intolerance. Lactose intolerance is transmitted in an autosomal recessive pattern. Acquired primary lactase deficiency is associated with a CC genotype at -13.9 kb upstream of the lactase gene. On gross and microscopic pathology, there are no characteristic findings of lactose intolerance.

# Causes
The most common cause of lactose intolerance is acquired primary lactase deficiency. Less common causes of lactose intolerance include Small intestinal bacterial overgrowth, Infections such as giardiasis, Drug induced enteritis, Celiac sprue, Tropical sprue, Whipple's disease.

# Differentiating Lactose Intolerance from other Diseases
The differential diagnosis must distinguish lactose intolerance from milk allergy, which is an abnormal immune response (usually) to milk proteins.

# Epidemiology and Demographics
The prevalence of lactose intolerance is approximately 75000 per 100,000 individuals worldwide. The prevalence of lactose intolerance is low in children younger than six years. Europeans and European Americans individuals are less likely to develop lactose intolerance. Lactose intolerance affects men and women equally. The majority of lactose intolerance cases are reported in the Far East

# Risk Factors
The most potent risk factor in the development of lactose intolerance is ethnicity. Other risk factors include increasing age, infection and drug.

# Screening
There is insufficient evidence to recommend routine screening for lactose intolerance.

# Natural History, Complications and Prognosis
If left untreated, patients with lactose intoelrance may progress to develop malnutrition, osteomalacia , and osteopenia. Common complications of lactose intoelrance include if they do not intake calcium include osteoprosis, osteopenia, osteomalacia and malnutrition. Prognosis is generally excellent.

# Diagnosis

## Diagnostic study of choice
Small bowel biopsy such as jejunal or duodenal biopsy is the gold standard test for the diagnosis of lactose intolerance. Low lactase activity in small bowel biopsy is confirmatory of lactose intolerance.The diagnostic study of choice for lactose intolerance is lactose breath hydrogen test. Lactose intolerance is diagnosed based on a rise in hydrogen concentration of 20 ppm ( parts per million) and presentation of symptoms such as bloating, diarrhea and abdominal pain.

## History and Symptoms
A positive history of abdominal pain and bloating after ingestion of milk-containing products is suggestive of lactose intolerance. Common symptoms of lactose intolerance include abdominal pain, bloating and flatulence. Less common symptoms of lactose intolerance include nausea, vomiting, and watery diarrhea.

## Physical Examination
Physical examination findings are usually normal. Borborygmi may be audible.

## Laboratory Findings
Laboratory tests include hydrogen breath test, stool acidity test, and intestinal biopsy. Since lactose intolerance is the normal state for most adults on a worldwide scale, and not considered a disease condition, diagnosis is not necessarily required.

## Electrocardiogram
There are no ECG findings associated with lactose intolerance.

## Chest X Ray
There are no x-ray findings associated with lactose intolerance.

## CT
There are no CT scan findings associated with lactose intolerance.

## MRI
There are no MRI findings associated with lactose intolerance.

## Echocardiography or Ultrasound
There are no echocardiography/ ultrasound findings associated with lactose intolerance.

## Other Imaging Findings
There are no other imaging findings associated with lactose intolerance.

## Other Diagnostic Studies
Lactose intolerance test may be helpful in the diagnosis of lactose intolerance. Findings suggestive of lactose intolerance include bloating, diarrhea and abdominal pain and rising of blood glucose by less than 20 mg/dL after ingestion of lactose. Genetic test can also be used for diagnosis of primary lactase deficiency that is associated with CC genotype at -13.9 kb upstream of the lactase gene.

# Treatment

## Medical Therapy
The mainstay of treatment for lactose intolerance is lifestyle modification that includes reducing dairy products from the diet and taking lactose-free or reduced lactose dairy products. Pharmacologic medical therapies for lactose intolerance include lactase enzyme preparations such as lactaid, lactogest, dairyease.

## Surgery
Surgical intervention is not recommended for the management of lactose intolerance.

## Primary Prevention
There are no established measures for the primary prevention of lactose intolerance.

## Secondary Prevention
Effective measures for the secondary prevention of lactose intolerance include reducing dairy products from the diet, taking lactose-free or reduced lactose dairy products and ingestion of lactaseenzyme tablets before eating the dairy product.