Residency · Residency · Medicine Pediatrics

Primary Immunodeficiency: Presentation and Lifelong Management

Overview

Primary immunodeficiencies (PIDs) are a group of >450 inborn errors of immunity with genetic basis. Estimated prevalence: ~1 in 1,200-2,000 live births (more common than previously recognized) Most present in childhood but some have delayed onset or are diagnosed in adulthood. Hallmark: increased susceptibility to infections, autoimmunity, inflammation, and malignancy. Early diagnosis and treatment dramatically improve outcomes.

Warning Signs of Primary Immunodeficiency

Jeffrey Modell Foundation Warning Signs (Pediatric)

>= 4 new ear infections in one year; >= 2 serious sinus infections in one year; >= 2 months on antibiotics with little effect; >= 2 pneumonias in one year; Failure to thrive; Recurrent deep skin or organ abscesses; Persistent thrush or fungal skin infections after age 1; Need for IV antibiotics to clear infections; >= 2 deep-seated infections (septicemia, meningitis, osteomyelitis); Family history of primary immunodeficiency.

Adult Warning Signs

Recurrent sinopulmonary infections (>= 2 per year requiring antibiotics); Bronchiectasis without known cause; Chronic diarrhea with weight loss; Recurrent herpes infections (oral, genital, or visceral); Autoimmune cytopenias (especially combined AIHA + ITP = Evans syndrome); Granulomatous disease without sarcoidosis or infection; Family history of immunodeficiency.

<image>Infographic showing the 10 warning signs of primary immunodeficiency in children with corresponding adult presentations and key differences by age group</image>

Classification by Immune Component

Combined Immunodeficiencies (T-cell +/- B-cell)

Severe Combined Immunodeficiency (SCID): Most severe form; fatal within first 1-2 years without treatment. Multiple genetic forms: X-linked (IL2RG, most common), ADA deficiency, RAG1/2 deficiency, IL-7R deficiency. Presentation: early-onset severe infections (PCP, CMV, disseminated BCG, persistent rotavirus), failure to thrive, chronic diarrhea, absent thymic shadow on CXR. Lymphopenia is the hallmark lab finding (absolute lymphocyte count <2,500 in neonates is concerning) Newborn screening: T-cell receptor excision circle (TREC) assay detects low T-cell numbers; now universal in US/Canada. Treatment: hematopoietic stem cell transplant (HSCT) — best outcomes if performed before age 3.5 months; gene therapy approved for ADA-SCID (Strimvelis) and X-linked SCID (investigational)

DiGeorge Syndrome (22q11.2 deletion): Thymic hypoplasia/aplasia, conotruncal cardiac defects, hypoparathyroidism (hypocalcemia), palatal abnormalities, facial dysmorphism. Variable T-cell deficiency (partial DiGeorge is more common than complete) Associated: developmental delay, behavioral differences, psychiatric illness (schizophrenia in adolescence/adulthood) Complete DiGeorge (<1% of T cells): requires thymus transplant. Partial DiGeorge: T-cell function often improves with age.

Predominantly Antibody Deficiencies (Most Common Group)

X-linked Agammaglobulinemia (XLA / Bruton disease): BTK gene mutation; absent B cells and all immunoglobulin classes. Boys present at 6-12 months (when maternal antibodies wane) with recurrent sinopulmonary infections, sepsis, meningitis. Absent or very small tonsils/lymph nodes (no B-cell follicles) Treatment: lifelong immunoglobulin replacement (IVIG or SCIG)

Common Variable Immunodeficiency (CVID): Most common symptomatic PID in adults. Low IgG + low IgA and/or IgM with poor vaccine responses. Peak diagnosis: 20-40 years (bimodal with smaller childhood peak) Infections: sinopulmonary (most common), GI. Non-infectious complications (often drive diagnosis): autoimmune cytopenias (20-25%), granulomatous-lymphocytic interstitial lung disease (GLILD), lymphoid hyperplasia, enteropathy, increased malignancy risk (lymphoma, gastric cancer) Treatment: IVIG or SCIG replacement; manage autoimmune and inflammatory complications.

Selective IgA Deficiency: Most common PID (1 in 300-700); most patients are asymptomatic. When symptomatic: recurrent sinopulmonary and GI infections, association with celiac disease, autoimmune conditions. Risk of anaphylaxis to blood products containing IgA (rare; screen with IgA level before transfusion if known IgA deficiency) No specific treatment; some evolve to CVID (monitor immunoglobulins)

Transient Hypogammaglobulinemia of Infancy: Delayed maturation of IgG production; physiologic nadir prolonged beyond normal; Usually resolves by age 2-4 years; Most children remain well; treatment rarely needed.

Phagocyte Defects

Chronic Granulomatous Disease (CGD): Defective NADPH oxidase in phagocytes; cannot generate respiratory burst to kill catalase-positive organisms. Infections: S. aureus, Aspergillus, Nocardia, Serratia, Burkholderia cepacia. Granuloma formation in lungs, liver, GI tract, lymph nodes. Diagnosis: dihydrorhodamine (DHR) flow cytometry (replaces nitroblue tetrazolium test) Treatment: TMP-SMX prophylaxis, itraconazole prophylaxis, interferon-gamma (controversial), HSCT (curative) X-linked (gp91phox) is most common; carrier mothers may have autoimmune features.

Leukocyte Adhesion Deficiency (LAD): Defective neutrophil adhesion and migration. Presentation: delayed umbilical cord separation (>30 days), severe bacterial infections without pus formation, very high WBC (neutrophilia due to inability to migrate to tissue) HSCT is curative.

Complement Deficiencies

Terminal complement deficiency (C5-C9): recurrent Neisseria infections (meningitis, gonorrhea) C3 deficiency: recurrent pyogenic infections (similar to antibody deficiency) C1q, C2, C4 deficiency: predispose to SLE (especially C1q) MBL deficiency: common (~5%); increased infection risk mainly when combined with other immune defects. Screen with CH50 (total complement); if abnormal, pursue individual component levels.

<image>Diagnostic algorithm for primary immunodeficiency showing initial screening tests (CBC with differential, quantitative immunoglobulins, complement levels, lymphocyte subsets) with branching to specific confirmatory testing based on suspected immune component defect</image>

Immunoglobulin Replacement Therapy

IVIG (Intravenous Immunoglobulin)

Dose: 400-600 mg/kg every 3-4 weeks. Administered in infusion center or hospital. Side effects: headache, fever, chills, nausea (rate-related); rare: aseptic meningitis, renal toxicity, thrombosis. Pre-medication with acetaminophen and diphenhydramine.

SCIG (Subcutaneous Immunoglobulin)

Dose: equivalent weekly dose (total monthly IVIG dose divided by number of weekly infusions) Self-administered at home by patient/family. More stable IgG trough levels; fewer systemic side effects. Local site reactions common (swelling, redness) but generally well-tolerated. Improves quality of life and independence, especially for adolescents/adults. Hyaluronidase-facilitated SCIG (HyQvia): allows larger volume subcutaneous infusion monthly.

Monitoring on Ig Replacement

Trough IgG levels: target >500-800 mg/dL (individualize based on clinical response) Monitor for end-organ damage: PFTs (bronchiectasis), CT chest periodically, LFTs. Infection log: frequency, severity, antibiotic use.

Newborn Screening for SCID

TREC Assay

T-cell receptor excision circles are byproducts of T-cell receptor gene rearrangement in the thymus. Low/absent TRECs indicate low T-cell production. Universal newborn screening in all US states and many countries. Detects: SCID (all forms), DiGeorge syndrome (severe), other causes of T-cell lymphopenia. False positives: prematurity (low TRECs normalize), cardiac surgery (low lymphocytes), trisomy 21. Positive screen: urgent confirmatory lymphocyte subset analysis (flow cytometry); immediate referral to immunology.

Impact of Newborn Screening

Pre-screening: most SCID diagnosed after life-threatening infection; transplant outcomes worse. Post-screening: diagnosis before infection; HSCT before age 3.5 months has >95% survival. Screening saves lives and is cost-effective.

Adult Presentation of PIDs

CVID in Adults

Often diagnosed years after symptom onset (diagnostic delay averages 4-9 years) Recurrent pneumonia leading to bronchiectasis is a common trajectory. Autoimmune complications may precede diagnosis (ITP, AIHA, autoimmune thyroiditis) Granulomatous disease mimicking sarcoidosis. GI: chronic diarrhea, nodular lymphoid hyperplasia, malabsorption, IBD-like enteropathy. Increased cancer risk: non-Hodgkin lymphoma (especially gastric MALT lymphoma), gastric carcinoma.

Late-Onset Combined Immunodeficiency (LOCID)

Subset of CVID with T-cell deficiency. Higher rates of opportunistic infections, malignancy, and granulomatous disease. May require prophylaxis similar to HIV (PCP, MAC)

Good Syndrome

Thymoma + immunodeficiency (hypogammaglobulinemia + low/absent B cells) Adults; presents with recurrent sinopulmonary infections, opportunistic infections (CMV, PCP) Thymectomy does not correct immunodeficiency. Requires lifelong Ig replacement.

<image>Comparison of clinical features, age of presentation, laboratory findings, and management approaches for XLA, CVID, IgA deficiency, and SCID highlighting the spectrum from mild to severe antibody and combined immunodeficiency</image>

Clinical Pearls

An absolute lymphocyte count <2,500 in a neonate is abnormal until proven otherwise — consider SCID. Never give live vaccines (rotavirus, MMR, varicella, BCG, live influenza) to a patient with suspected or confirmed T-cell deficiency — disseminated infection can be fatal. CVID cannot be diagnosed before age 4 (earlier, consider transient hypogammaglobulinemia of infancy); requires exclusion of secondary causes (medications, nephrotic syndrome, protein-losing enteropathy) Vaccine responses help distinguish primary antibody deficiency from secondary causes — check pre- and post-immunization titers to pneumococcal polysaccharide antigens. CGD patients with Aspergillus need aggressive antifungal therapy — Aspergillus is the leading cause of death in CGD. IgA-deficient patients can have anaphylaxis to blood products containing IgA — use washed RBCs or IgA-deficient donor products if transfusion needed. Bronchiectasis in a young adult without cystic fibrosis should prompt immunoglobulin levels and vaccine response evaluation — CVID is a leading cause. Family history is often negative because many PIDs are X-linked (carrier mothers are unaffected) or autosomal recessive — absence of family history does not exclude PID.

References

• Tangye SG, Al-Herz W, Bousfiha A, et al. Human Inborn Errors of Immunity: 2022 Update on the Classification from the IUIS Expert Committee. J Clin Immunol. 2022;42(7):1473-1507.
• Bonilla FA, Khan DA, Ballas ZK, et al. Practice Parameter for the Diagnosis and Management of Primary Immunodeficiency. J Allergy Clin Immunol. 2015;136(5):1186-1205.
• Kwan A, Abraham RS, Currier R, et al. Newborn Screening for Severe Combined Immunodeficiency in 11 Screening Programs in the United States. JAMA. 2014;312(7):729-738.
• Ameratunga R, Woon ST, Gillis D, et al. New Diagnostic Criteria for CVID. Clin Exp Immunol. 2013;174(2):203-211.

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