Cow's Milk protein allergy

Definition and Pathophysiology

Definition

Cow's Milk Protein Allergy (CMPA) is an immunologically mediated adverse reaction to one or more proteins present in cow's milk (primarily caseins and whey proteins like beta-lactoglobulin and alpha-lactalbumin). It is distinct from non-immunological cow's milk intolerance (e.g., lactose intolerance).

Pathophysiology

CMPA is categorized into three distinct immunological mechanisms:

• IgE-Mediated: Type I hypersensitivity reaction. Exposure triggers cross-linking of surface IgE on mast cells and basophils, causing immediate degranulation and release of vasoactive amines (histamine, leukotrienes).
• Non-IgE-Mediated: Type IV cell-mediated hypersensitivity or localized T-cell and eosinophilic infiltration. Driven by antigen-specific T-cells causing subacute or chronic localized inflammation, primarily within the gastrointestinal tract.
• Mixed (IgE and Non-IgE) Mechanism: Features overlap of both immediate and delayed cellular inflammatory responses.

Clinical Features and Phenotypes

Presentation Timelines

• Immediate Reactions (IgE-mediated): Occur within minutes up to 2 hours post-ingestion.
• Delayed Reactions (Non-IgE mediated): Occur hours to days (up to 1–2 weeks) following chronic ingestion.

Target Organ Manifestations

• Gastrointestinal: Vomiting, diarrhea, abdominal pain/infantile colic, hematochezia (blood in stools), dysphagia, food refusal, failure to thrive (FTT), and perianal erythema.
• Cutaneous: Acute urticaria, angioedema, atopic dermatitis (moderate to severe, subacute or chronic flare-ups).
• Respiratory: Rhinorrhea, chronic wheezing, stridor, persistent dry cough. Anaphylaxis represents the severe, life-threatening systemic manifestation.

Recognized Non-IgE/Mixed Phenotypes

• Food Protein-Induced Allergic Proctocolitis (FPIAP): Typically presents in healthy-appearing, breastfed or formula-fed young infants (1–4 months) with blood-streaked, mucoid stools without systemic illness or growth failure.
• Food Protein-Induced Enteropathy (FPIE): Characterized by chronic diarrhea, malabsorption, steatorrhea, iron deficiency anemia, and failure to thrive.
• Food Protein-Induced Enterocolitis Syndrome (FPIES): A severe phenotype presenting 1–4 hours post-ingestion with profuse, repetitive projectile vomiting, diarrhea, lethargy, dehydration, and systemic hypotension mimicking septic shock.
• Eosinophilic Gastrointestinal Disorders (EGIDs): Eosinophilic Esophagitis (EoE) or Gastroenteritis, presenting with food impaction, reflux refractory to acid suppression, and dysphagia.

Diagnostic Evaluation

Clinical Diagnostics

Diagnosis rests heavily on a detailed clinical history, physical examination, and structured elimination-challenge protocols.

Diagnostic Algorithms by Mechanism

• For Suspected IgE-Mediated CMPA:
  • Skin Prick Testing (SPT): Demonstrates localized wheal-and-flare response; high negative predictive value (>95%).
  • Serum Specific IgE (sIgE) Quantification: ImmunoCap assays measuring circulating IgE levels against whole cow's milk extract or specific molecular components ($nBosd8$ [casein], $nBosd4$, $nBosd5$).
• For Suspected Non-IgE-Mediated CMPA:
  • SPT and sIgE are characteristically negative.
  • Diagnostic relies strictly on a Diagnostic Elimination Diet followed by an Oral Food Challenge (OFC).

Reference Standard Test

• Double-Blind, Placebo-Controlled Food Challenge (DBPCFC): The diagnostic gold standard.
• In clinical practice: An open oral food challenge (OFC) is typically used after a 2-to-4 week elimination period, provided it is performed under strict medical supervision equipped to manage anaphylaxis.

Supplementary Investigations

• Stool Examination: To document occult/gross blood, fecal leukocytes, or elevated fecal calprotectin (non-specific marker of bowel inflammation).
• Endoscopy and Biopsy: Reserved for atypical cases, suspected FPIE, or EoE. Histology reveals mucosal inflammation, villous atrophy, or intraepithelial eosinophilic infiltration (>15 eosinophils per high-power field in EoE).

Therapeutic Management

General Dietary Principles

Absolute avoidance of cow's milk protein from the infant's diet. If the infant is exclusively breastfed, the mother must implement a strict cow's milk-free diet, supplemented with calcium (1000 mg/day) and Vitamin D.

First-Line Specialized Formulations

For formula-fed infants, choice of formula depends on clinical severity: