Child Interstitial Lung Disease (chILD)

I. Definition

Interstitial Lung Disease (ILD) refers to a heterogeneous group of rare respiratory disorders affecting the pulmonary parenchyma (alveoli, distal airways, and interstitium).

• Pathology: Characterized by inflammation and/or fibrosis of the interalveolar septa, leading to impaired gas exchange and diffuse infiltrates on imaging.
• Pediatric Context: Unlike adults, "chILD" encompasses developmental disorders and growth abnormalities specific to the developing lung.

II. Classification of Pediatric ILDs

The classification is age-dependent (American Thoracic Society / chILD Foundation).

A. Disorders More Prevalent in Infancy (less than 2 years)

1. Diffuse Developmental Disorders:
   • Acinar Dysplasia.
   • Congenital Alveolar Dysplasia.
2. Growth Abnormalities:
   • Pulmonary Hypoplasia.
   • Chronic Lung Disease of Prematurity (BPD).
3. Specific Conditions of Unknown Etiology:
   • Neuroendocrine Hyperplasia of Infancy (NEHI): Benign, "noisy breather."
   • Pulmonary Interstitial Glycogenosis (PIG).
4. Surfactant Dysfunction Mutations:
   • SFTPB, SFTPC, ABCA3 mutations.

B. Disorders More Prevalent in Older Children (>2 years)

1. Systemic Disease Associated:
   • Connective Tissue Disease (SLE, JIA).
   • Sarcoidosis.
   • Langerhans Cell Histiocytosis (LCH).
2. Environmental/Inhalational:
   • Hypersensitivity Pneumonitis (e.g., Bird fancier's lung).
3. Immunocompromised Host:
   • Opportunistic infections (PCP, CMV).
   • Graft-vs-Host Disease (GVHD).

III. Lymphocytic Interstitial Pneumonitis (LIP)

A benign lymphoproliferative disorder characterized by diffuse infiltration of the interstitium by mature polyclonal lymphocytes.

• Etiology/Association:
  • HIV/AIDS: LIP is an AIDS-defining illness in children (rare in adults).
  • Autoimmune: Sjögren’s syndrome, SLE.
  • Immunodeficiency: CVID (Common Variable Immunodeficiency).
• Pathology: Alveolar septal infiltration with lymphocytes, plasma cells, and histiocytes. Lymphoid follicles may form.
• Clinical Features:
  • Insidious onset of cough and dyspnea.
  • Painless generalized lymphadenopathy and parotid enlargement (classic in HIV-LIP).
  • Clubbing is common.
• Diagnosis:
  • HRCT: Ground-glass opacities and cysts.
  • Biopsy: Required for confirmation.
• Prognosis: Variable. HIV-associated LIP often improves with HAART; autoimmune forms may progress to lymphoma (rare).

IV. Treatment Options for ILD in Children

Management is often empirical due to the rarity of randomized trials.

1. Supportive Care (The Cornerstone)

• Oxygen Therapy: Maintain SpO2 >92–95% to prevent pulmonary hypertension.
• Nutrition: High-calorie diet (increased work of breathing causes failure to thrive).
• Vaccination: Annual Influenza, Pneumococcal, and RSV prophylaxis (if eligible).
• Avoidance: Removal of environmental antigens (e.g., birds, mold) if Hypersensitivity Pneumonitis is suspected.

2. Pharmacotherapy

• Systemic Corticosteroids (First Line):
  • Oral Prednisolone: 1–2 mg/kg/day.
  • Pulse Methylprednisolone: 10–30 mg/kg/day for 3 days monthly (preferred for rapid control with fewer side effects).
• Steroid-Sparing Agents (Second Line):
  • Hydroxychloroquine (HCQ): Often used for surfactant protein disorders (SP-C) and stable ILD.
  • Azithromycin: For anti-inflammatory and immunomodulatory effects.
• Immunosuppressants (Refractory Cases):
  • Azathioprine, Mycophenolate Mofetil, or Cyclophosphamide.
  • Rituximab: For autoimmune-associated ILD.

3. Advanced/Surgical Options

• Lung Transplantation: The final option for end-stage fibrosis or surfactant protein B deficiency (fatal without transplant).