STEPTRACKERRESPIRATORY | PATHOLOGY + IMMUNOLOGY | HIGH-YIELD REVIEW

Sarcoidosis & Hypersensitivity Pneumonitis

Noncaseating granulomatous lung diseases — one with an unknown trigger and many organs, one with an inhaled antigen you can avoid.

FOCUS ON
Sarcoidosis: young Black woman, bilateral hilar adenopathy, noncaseating granulomas, ↑ ACE, hypercalcemia (macrophage 1α-hydroxylase), ↑ CD4:CD8 ratio. Know Löfgren and Heerfordt syndromes. HP: inhaled organic antigen (hay, birds, hot tubs), type III + IV, improves when exposure stops.
TOPIC
DETAIL
MECHANISM
CLUE
Sarcoidosis — who & why
Young adults; Black women in the US; Northern Europeans.
Th1 (CD4) response to an unknown antigen → noncaseating granulomas in many organs
Diagnosis of exclusion
Lungs & nodes
Bilateral hilar lymphadenopathy, often found incidentally; interstitial disease (restrictive) with dry cough, dyspnea.
Granulomas along lymphatics
Can progress to upper-lobe fibrosis
Skin & eyes
Erythema nodosum, lupus pernio (violaceous nose/cheeks), skin nodules; anterior uveitis.
Granulomas / panniculitis
Löfgren: BHL + erythema nodosum + ankle arthritis + fever → good prognosis
Other organs
Heart (heart block, restrictive CM, sudden death), CNS (facial palsy, diabetes insipidus), parotids, liver, marrow, kidney.
Granulomatous infiltration
Heerfordt: uveitis + parotitis + facial palsy + fever
Labs
↑ ACE, hypercalcemia/hypercalciuria, ↑ CD4:CD8 in BAL, hypergammaglobulinemia, cutaneous anergy.
Granuloma macrophages make ACE and calcitriol (1α-hydroxylase)
Kidney stones; PPD may be negative
Pathology & treatment
Tight noncaseating granulomas with Schaumann bodies (laminated calcium) and asteroid bodies (stellate inclusions in giant cells).
Often remits on its own
Steroids for organ-threatening disease
Hypersensitivity pneumonitis
Inhaled organic antigens: farmer's lung (thermophilic actinomycetes in moldy hay), bird fancier's lung, hot-tub lung (MAC), humidifiers.
Type III (acute) + type IV (chronic); loose peribronchiolar granulomas; ↑ CD8 lymphocytes in BAL
Fever, cough, dyspnea hours after exposure · chronic → upper-lobe fibrosis · avoid antigen, steroids
Eosinophilic lung disease
Löffler syndrome (migrating parasite larvae — Ascaris, Strongyloides — or drugs), chronic eosinophilic pneumonia, ABPA, EGPA.
Eosinophil-rich infiltrates
Chronic eosinophilic pneumonia: peripheral "photographic negative" of pulmonary edema

Mechanism — the sarcoid granuloma

Unknown antigen
→
APC → CD4 Th1IL-2, IFN-γ
→
Epithelioid cells, giant cellsNoncaseating granuloma
→
Macrophage productsACE, calcitriol → ↑ Ca²⁺

T cells pile into granulomas, so the blood has fewer of them — explaining skin-test anergy.

Granulomatous lung diseases compared

FEATURE
SARCOIDOSIS
HYPERSENSITIVITY PNEUMONITIS
TB
Granuloma
Tight, noncaseating
Loose, peribronchiolar
Caseating
Trigger
Unknown
Inhaled organic antigen
M tuberculosis
Nodes
Bilateral hilar
Not prominent
Hilar (primary)
BAL
CD4:CD8 ↑
CD8 lymphocytes ↑
AFB
Calcium
Often ↑
Normal
Sometimes ↑

How it's tested

COMMON CONFUSIONNoncaseating granulomas also appear in berylliosis, HP, Crohn and foreign-body reactions. Always ask about exposures before calling it sarcoidosis.
THE TRAPA sarcoid patient with kidney stones and confusion has hypercalcemia from macrophage calcitriol. PTH is suppressed, and steroids fix it.
YOUR APPROACHGranulomas + no caseation → exposure history (beryllium, birds, hay) → hilar nodes and systemic signs → sarcoidosis if nothing else fits.

If you see… think…

Young Black woman with bilateral hilar nodes, ↑ ACE, ↑ Ca²⁺ → sarcoidosis
Hilar nodes + erythema nodosum + ankle arthritis + fever → Löfgren syndrome
Violaceous plaques on the nose → lupus pernio
Uveitis + parotid swelling + facial palsy → Heerfordt syndrome
Asteroid and Schaumann bodies in granulomas → sarcoidosis
Sarcoid patient with syncope and heart block → cardiac sarcoid
Farmer with fever and cough hours after moving moldy hay → farmer's lung
Pigeon keeper with recurrent dyspnea → bird fancier's lung
Hot-tub user with granulomatous pneumonitis → MAC "hot-tub lung"
Migratory infiltrates + eosinophilia after travel → Löffler syndrome (Ascaris)