Granulomatous Inflammation MCQ — NEET PG Practice Question | NEETPGAI
Granulomatous Inflammation
medium
microscope Pathology
A 28-year-old woman from Maharashtra with a 6-month history of painless nodules on the shins, fever, and cough undergoes chest imaging showing bilateral hilar lymphadenopathy. Skin biopsy of the nodule shows non-caseating granulomas. Which investigation would be most appropriate to differentiate this condition from tuberculosis?
A. Caseation necrosis assessment on repeat biopsy of the same lesion
B. Interferon-gamma release assay (TB-IGRA)
C. Sputum smear microscopy for acid-fast bacilli
D. Serum lysozyme level
Explanation
Differentiating Sarcoidosis from Tuberculosis
Clinical Presentation
The patient presents with the classic triad of Löfgren syndrome (acute sarcoidosis):
Erythema nodosum (painless nodules on shins)
Bilateral hilar lymphadenopathy
Constitutional symptoms (fever, cough)
The skin biopsy already demonstrates non-caseating granulomas, which is the hallmark of sarcoidosis. The critical question is: which investigation best differentiates this from tuberculosis, especially in an endemic region like Maharashtra, India?
Why TB-IGRA (Interferon-Gamma Release Assay) is the Most Appropriate Investigation
High-YieldNEET PG
In a patient where the biopsy has already shown non-caseating granulomas, the TB-IGRA (QuantiFERON-TB Gold or T-SPOT.TB) is the most appropriate investigation to differentiate sarcoidosis from tuberculosis because:
1.
Specificity for Mycobacterium tuberculosis: IGRA detects T-cell responses to TB-specific antigens (ESAT-6 and CFP-10), which are absent in M. bovis BCG and most non-tuberculous mycobacteria. A negative IGRA strongly supports sarcoidosis over TB.
2.
Non-invasive and practical: It requires only a blood sample and does not require repeating an invasive biopsy.
3.
Endorsed by guidelines: In TB-endemic countries, IGRA is recommended as a key tool to rule out TB infection when sarcoidosis is suspected (Harrison's 21e, Ch. 335; RNTCP guidelines).
4.
Sarcoidosis patients typically test IGRA-negative (unless co-infected), whereas active or latent TB patients test positive.
Table
Investigation
Sensitivity for TB
Specificity for TB vs. Sarcoidosis
Practicality
TB-IGRA
~80–90%
High (TB-specific antigens)
Blood test, non-invasive
Sputum AFB smear
40–60%
Low (negative in both)
Requires sputum, 3 samples
Repeat biopsy for caseation
N/A
Moderate (already non-caseating)
Invasive, redundant
Serum lysozyme
N/A
Low (elevated in both)
Non-specific
Why Other Options Are Suboptimal
Option B – Caseation necrosis on repeat biopsy:
The biopsy has already been performed and shows non-caseating granulomas. Repeating the biopsy to assess caseation is redundant and invasive.
AFB staining on the existing biopsy specimen would be more logical, but even that is less definitive than IGRA.
Repeating biopsy is not standard clinical practice for this differential.
Option A – Sputum smear microscopy for AFB:
Sensitivity is only 40–60% for pulmonary TB; a negative result does not rule out TB.
Completely negative in sarcoidosis, so it cannot reliably differentiate the two conditions.
Option D – Serum lysozyme:
Elevated in sarcoidosis but also in TB and other granulomatous diseases.
Non-specific; not used for differentiation in routine clinical practice.
Diagnostic Approach
Clinical Pearl
In TB-endemic regions like India, TB-IGRA is the investigation of choice to exclude TB when non-caseating granulomas are found on biopsy. A negative IGRA, combined with the clinical picture of Löfgren syndrome, strongly supports a diagnosis of sarcoidosis. Serum ACE and calcium levels provide additional supportive evidence.
Harrison 21e Ch. 335; Robbins & Cotran Pathologic Basis of Disease 10e Ch. 15; RNTCP/NTEP Guidelines
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