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.

How to think about this

Primary immunodeficiencies (PIDs) are a broad and increasingly recognized group of genetic disorders that result in impaired immune function, leading to a variety of clinical manifestations beyond just recurrent infections. While many present in childhood, it's crucial to remember that PIDs can manifest at any age, with some common types like Common Variable Immunodeficiency (CVID) often diagnosed in adulthood after years of non-specific symptoms. A key takeaway is that these conditions are not always rare; for example, Selective IgA Deficiency is quite common, though often asymptomatic. Think of PIDs as disorders of immune regulation that can predispose to infections, autoimmunity, inflammation, and malignancy. Early recognition, even in adults, and appropriate management with immunoglobulin replacement or, in some cases, hematopoietic stem cell transplant (HSCT), significantly improves patient outcomes and quality of life.

Check yourself with 2 bullets.

• What are the hallmark clinical features that should make you consider a primary immunodeficiency in an adult patient, even if they don't fit the classic pediatric warning signs?
• Beyond infections, what other major categories of complications are associated with primary immunodeficiencies, and why is this understanding important for long-term patient management?

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