Allergic colitis overview

# Overview
Allergic colitis is a non IgE immunological reaction against food protein antigens, particularly cow-milk and soy proteins. The exact mechanism is not known. It usually develops insidiously, and is believed to be T-cell mediated. Allergic colitis is most commonly caused by allergy to cow's milk protein. Symptoms and signs of allergic colitis are non-specific and observed in other causes of colitis and some systemic diseases. Detailed history and physical examination is needed to make the diagnosis. In addition, endoscopy with biopsy may be required to confirm the diagnosis. The exact prevalence of allergic colitis is unknown. Allergic colitis typically develops in early infancy. Allergic colitis is benign, resolving completely in most children without any sequelae. The most common symptoms of allergic colitis is passage of blood streaked stool in an otherwise healthy young infant. There are no specific laboratory findings that are pathognomonic of allergic colitis. Laboratory studies should therefore be correlated with a carefully taken history and a detailed physical examination. Presence of eosinophils in the stool is suggestive of allergic colitis in the presence of typical clinical findings. The mainstay of treatment of allergic colitis is dietary management. Medical therapy includes allergen avoidance, treatment of severe manifestations of the allergy, and eventual reintroduction of the allergy into the diet.

# Historical Perspective
Allergic colitis was first described by Kaijser in 1937. Allergic proctocolitis was described by Rubin in 1940. In the 1960s, Gryboski subsequently described proctocolitis and enterocolitis.

# Classification
Allergic colitis can be classified into two subtypes based on the anatomical site involved, proctocolitis and enterocolitis. Allergic colitis manifests more commonly as proctocolitis. It is also more common among infants.

# Pathophysiology
Allergic colitis is a non IgE immunological reaction against food protein antigens, particularly cow-milk and soy proteins. The exact mechanism is not known. It usually develops insidiously, and is believed to be T-cell mediated. The activated T-cells lead to recruitment of eosinophils and other polymorphonuclear cells into the intestinal tract, which then cause intestinal inflammation and damage. Some of these children may later develop specific IgE. Genetic influence may also play a role, since disease is sometimes present within families. On gross pathology, there is evidence of inflammation with ulcers and friable, erythematous mucosa. On microscopy, the mucosa architecture is preserved with eosinophil infiltrates.

# Causes
Allergic colitis is most commonly caused by allergy to cow's milk protein. 20-40% of patients with allergic colitis have allergies to both cow's milk protein and soy protein.

# Differential Diagnosis
Symptoms and signs of allergic colitis are non-specific and observed in other causes of colitis and some systemic diseases. Detailed history and physical examination is needed to make the diagnosis. In addition, endoscopy with biopsy may be required to confirm the diagnosis. In infancy, allergic colitis must particularly be differentiated from necrotizing enterocolitis, infectious colitis, anal fissure, intussusception, and volvulus. In adolescent and adults, allergic colitis must be differentiated from inflammatory bowel disease, infectious colitis, and colorectal malignancy.

# Epidemiology and Demographics
The exact prevalence of allergic colitis is unknown. Prevalence of food protein-induced allergic proctocolitis (FPIAP) has been reported to range from a low of 16% to a high of 64% among infants with rectal bleeding. FPIAP is the most common cause of non-infectious colitis in infancy. Allergic colitis is mainly a disease of infants, with onset usually in the first two to three months of life. There is a slight male predominance (5061.6%) for allergic colitis.

# Risk Factors
Risk factors for allergic colitis include family history of atopy and previous sibling with IgE mediated food allergy.

# Screening
Screening is not recommended for allergic colitis.

# Natural History, Complications, and Prognosis
Allergic colitis typically develops in early infancy. Allergic colitis is benign, resolving completely in most children without any sequelae. The infants with food protein-induced allergic proctocolitis are usually on exclusive breastfeeding while those with food protein-induced enterocolitis syndrome are often on infant formula. If left untreated, spontaneous resolution may occur in 20% of the children with allergic colitis without elimination of the triggering food. Most infants with allergic colitis will tolerate the offending food by 1 to 3 years of age.

# Diagnosis

## History and Symptoms
The most common symptoms of allergic colitis is passage of blood streaked stool in an otherwise healthy young infant especially in FPIAP. History of failure to thrive may also be gotten in the infant with FPIES. There may be a family history of allergy.

## Physical Examination
Patients with allergic colitis may appear well in the case of FPIAP or may appear lethargic when they have FPIES. Physical examination of patients with FPIES is usually remarkable for signs of dehydration, pallor, and poor weight.

## Laboratory Findings
There are no specific laboratory findings that are pathognomonic of allergic colitis. Laboratory studies should therefore be correlated with a carefully taken history and a detailed physical examination. Presence of eosinophils in the stool is suggestive of allergic colitis in the presence of typical clinical findings.

## Imaging Findings

### X Ray
There are no diagnostic x ray findings associated with allergic colitis.

### CT
There are no diagnostic CT findings associated with allergic colitis.

### MRI
There are no diagnostic MRI findings associated with allergic colitis.

### Ultrasound
There are no diagnostic ultrasound findings associated with allergic colitis.

## Other Imaging Findings
Other imaging studies for allergic colitis include endoscopy. Endoscopy is not recommended in the routine diagnosis of allergic colitis. Endoscopy is usually required for atypical presentation in addition to detailed clinical assessment. The lesions in allergic colitis are most often observed in the the rectosigmoid area. Gross endoscopic findings associated with allergic colitis include; focal or diffuse erythema, edematous and friable mucosa, with nodular hyperplasia and/ or ulcerations. Characteristic circumscribed central pit-like erosions may also be observed.

# Other Diagnostic Studies
There are no additional diagnostic studies associated with allergic colitis.

# Treatment

## Medical Therapy
The mainstay of treatment of allergic colitis is dietary management. Medical therapy includes allergen avoidance, treatment of severe manifestations of the allergy, and eventual reintroduction of the allergy into the diet.

## Surgery
There is no indication for surgical intervention in allergic colitis.

## Primary Prevention
There are presently no established methods to prevent allergic colitis.

## Secondary Prevention
There are presently no secondary preventive measures for allergic colitis. However, it is important to avoid food allergens identified in the individual until tolerance has been demonstrated.