Chest Expansibility - Normal Value (Macleod's)

How it is measured:

• The circumference of the chest is measured at the level of the 4th intercostal space (nipple level in men).
• Measured first at full expiration, then at full inspiration.
• The difference between the two readings = chest expansibility.
• Normal = 5 cm or more.

Clinical significance:

Key causes of reduced chest expansion:

• Unilateral reduction: Pleural effusion, pneumothorax, consolidation, collapse, fibrosis
• Bilateral reduction: COPD (hyperinflation), Ankylosing Spondylitis (costovertebral fusion), bilateral pleural disease, obesity

Note: In Ankylosing Spondylitis, a chest expansion of < 2.5 cm has good specificity (though poor sensitivity) for the diagnosis, and it is one of the modified New York criteria for AS. - Washington Manual of Medical Therapeutics; Firestein & Kelley's Textbook of Rheumatology

Ankylosing Spondylitis (AS)

Definition

Epidemiology

• Prevalence: ~0.2% of the general population
• ~2% of HLA-B27 positive individuals develop AS
• ~20% of HLA-B27 positive individuals with an affected family member develop AS
• Male : Female = 3 : 1 (historically up to 5:1, but more recent studies show lower ratio)
• Onset: typically young adults, can begin in adolescence

Pathogenesis (Pathobiology)

• Strongly associated with HLA-B27 (90% of patients)
• HLA-B27 has a unique tendency to misfold in the endoplasmic reticulum, triggering a pro-inflammatory cascade called the unfolded protein response
• HLA-B27 also forms heavy-chain homodimers on the cell surface, contributing to inflammation
• Molecular mimicry with gram-negative enteric bacteria has been proposed
• Gut microbiome plays a role - germ-free HLA-B27 transgenic rats show markedly reduced joint disease
• Inflammation begins at entheses (sites where ligaments/tendons insert into bone), especially around the sacroiliac joints and spine

Clinical Features

Axial Symptoms (Primary)

• Chronic low back pain lasting > 3 months
• Inflammatory pattern: worse in the morning, improves with exercise, NOT relieved by rest
• Early-morning stiffness (often lasting hours)
• Pain around sacroiliac joints, may radiate to buttocks
• Back pain that wakes the patient from sleep is a red flag for inflammatory back pain
• Fatigue is common

As Disease Progresses

• Progressive loss of spinal mobility
• Reduced chest expansion (< 2.5 cm is specific for AS)
• Forward stoop / kyphosis

Peripheral Joint Involvement (~30%)

• Asymmetric oligoarthritis, predominantly lower limbs
• Hip joints - second most commonly affected (after sacroiliac joints)
• Enthesitis: Achilles tendinitis, plantar fasciitis (heel pain)

Extra-articular Manifestations

MRI of Sacroiliac Joints in AS

MRI of Thoracic Spine in AS

Radiology

Note: Spinal fractures are a serious complication - the fused, osteopenic spine is paradoxically brittle and transverse fractures can be catastrophic.

Diagnostic Criteria

Modified New York Criteria for AS

1. Low back pain and stiffness for > 3 months, improves with exercise but not rest
2. Limitation of lumbar spine motion in both sagittal and frontal planes
3. Limitation of chest expansion

• Sacroiliitis: grade ≥2 bilateral, or grade 3-4 unilateral

Differential Diagnosis

Treatment

• Anti-TNF agents (e.g., infliximab, adalimumab, etanercept) - first-line biologic
• IL-17 inhibitors (e.g., secukinumab, ixekizumab) - strongly recommended for active AS with inadequate NSAID response; preferred over TNF inhibitors in patients with demyelinating disease risk

Causes of Tracheal Deviation

The Core Principle (Easy Memory Rule)

Causes: Trachea Deviated AWAY from the Lesion (Pushed)

1. Tension pneumothorax - most urgent/life-threatening cause; air under pressure pushes trachea away
2. Massive pleural effusion - large fluid accumulation pushes trachea to opposite side
3. Large haemothorax
4. Diaphragmatic hernia - abdominal contents herniate into chest, pushing mediastinum
5. Large mediastinal mass / tumour - e.g., lymphoma, thymoma
6. Aortic aneurysm - displaces trachea
7. Multinodular goiter / large thyroid mass - enlarged thyroid can deviate trachea to the contralateral side

On chest X-ray: tracheal deviation AWAY from an opacified (white) hemithorax = volume-occupying process (e.g., pleural effusion). - Frameworks for Internal Medicine

Causes: Trachea Deviated TOWARD the Lesion (Pulled)

1. Pulmonary collapse / atelectasis - most common; lung collapses, pulling trachea toward it
2. Pulmonary fibrosis - scarring contracts the lung, pulling trachea ipsilaterally
3. Pleural fibrosis - fibrothorax/old empyema with fibrosis
4. Post-pneumonectomy - removal of a lung pulls trachea to that side
5. Post-lobectomy (if large enough)
6. Phrenic nerve palsy with subsequent lung collapse

On chest X-ray: tracheal deviation TOWARD an opacified (white) hemithorax = volume-losing process (e.g., atelectasis, collapse, fibrosis). - Frameworks for Internal Medicine

Quick Summary Table

Important Clinical Note

• In simple (non-tension) pneumothorax, tracheal deviation is usually absent - it only occurs with tension pneumothorax when pressure is sufficient to shift the mediastinum.
• Pemberton's sign: Raising both arms above the head can worsen tracheal compression/deviation from a large goiter, causing facial flushing and respiratory distress.
• Tracheal compression > 70% of the tracheal diameter is usually required before significant airway compromise occurs (e.g., from goiter). - Harrison's Principles of Internal Medicine, 22nd Ed.

Retrosternal Goiter (Intrathoracic Goiter)

Definition / "Kya hoti hai?"

1. Any goiter that extends below the thoracic inlet (with patient in surgical position), OR
2. Any goiter where more than 50% of the gland lies below the thoracic inlet

Types

Chest X-Ray - Primary Intrathoracic Goiter

Why Does It Grow Downward? (Aetiology)

• Neck musculature obstructs extra-thoracic growth, directing the goiter downward
• Negative intrathoracic pressure and downward traction from swallowing pull it into the chest
• 90% grow into the anterior mediastinum; only 10-15% grow into the posterior mediastinum
• Majority are right-sided - because the great vessels (aorta) impede extension into the left thorax

Clinical Presentation

Asymptomatic

• Up to 40% are asymptomatic, discovered incidentally on chest X-ray
• May present as a barely palpable or impalpable neck mass (majority of thyroid is in the chest)

Symptomatic (due to compression)

Pemberton's Sign (IMPORTANT)

When both arms are raised above the head, facial congestion, cyanosis, and respiratory distress appear - indicating increased thoracic inlet pressure from the retrosternal mass. This is pathognomonic of retrosternal goiter.

Investigations

1. Thyroid function tests (TFTs/TSH) - most are euthyroid (80%); up to 30% have subclinical thyrotoxicosis
2. Ultrasound - good for cervical thyroid; cannot assess intrathoracic component
3. CT scan - best imaging modality for intrathoracic extension; shows extent, tracheal deviation/compression, mediastinal compartment involved
   • Sternotomy more likely needed if goiter extends below the aortic arch
4. MRI - useful for defining relationship with surrounding structures
5. Radionuclide scan (¹²³I / ¹³¹I) - confirms thyroid origin; primary intrathoracic goiters often show reduced iodine avidity
6. Flow-volume loop spirometry - to assess respiratory compromise (but correlates poorly with goiter weight)

Rule: If you cannot palpate the distal extent of a goiter, CT scan is mandatory.

Management

Non-Surgical Options

Surgery (Main Treatment)

• Surgery is indicated when trachea is compressed by ≥35% on axial CT (American Thyroid Association guideline)
• Route of surgery:
  • Cervical approach (standard) - used in >95% of cases; retrosternal portion delivered into operative field by dividing isthmus and taking down superior pole
  • Sternotomy - required if goiter extends below aortic arch or malignancy suspected; carries 25% risk of respiratory complications vs 2% for cervical approach
• Blood supply: Secondary intrathoracic goiter is ligated via neck vessels (superior/inferior thyroid arteries), NOT from thoracic vessels - this is why most can be removed via a cervical incision

Risks to Remember

• Recurrent laryngeal nerve injury
• Hypoparathyroidism
• Spontaneous intraglandular haemorrhage → acute respiratory distress (rare but real risk)
• Patients with retrosternal goiter tend to be older, frailer, with higher surgical risk