Sarcoidosis is a relatively common disease of unknown etiology, characterized by multiple, uniform, discrete, noncaseating granulomas in almost any organ of the body. The lymphnodes and the lung are most commonly involved.

Visit:  Infectious Granuloma of the Lung  ; Pathological Diagnosis of Granulomatous Lung Diseases ; Non-necrotising Granulomatous Inflammation of the lung ; An approach to Histopathological examination of Pulmonary Granulomatous Inflammation ;

In pulmonary sarcoidosis radiologically, there is a diffuse reticulonodular infiltrate, but in occasional cases larger nodules are present, a situation referred to as nodular or alveolar sarcoidosis.

Pulmonary sarcoidosis is apparent by lung and hilar lymph node involvement, lymph node enlargement alone or lung disease.

Microscopic features:

Histologically, involvement of both lung and lymph nodes occurs in nearly all instances.

Multiple sarcoid nodules are scattered in the interstitium, particularly in relation to lymphatics, that is, in the bronchovascular bundle and in the lobular septa.

 There is increased cellularity of the alveolar walls, owing to an infiltrate of mononuclear cells.

The central part of the granuloma is fibrotic and surrounded by palisaded histiocytes.  In about 60 % cases, Schaumann bodies (laminated calcified proteinaceous concretions) and asteroid bodies (stellate inclusions within giant cells) are found.

Giant cells at the periphery resemble those of the tuberculosis.

The cuff of lymphocytes that surrounds the histiocytes is inconspicuous, compared with tuberculosis , hence the term “naked tubercle”.

Granulomas also occur in the airways and occasionally may be so prominent as to lead to airway obstruction (endobronchial sarcoid).

Pulmonary lesions have strong tendency to heal, so that only hyalinized scars may be seen microscopically.

The effects on pulmonary function are highly variable.

There may be no abnormalities, classic restrictive lung disease, chronic airflow obstruction, or a mixture of restrictive and obstructive lung disease.

Clinical presentation:

Women are more commonly affected.

Sarcoidosis may be asymptomatic and diagnosed at autopsy or as bilateral hilar adenopathy on a chest x-ray taken for other reasons.

The patients may present as isolated cutaneous or ocular lesions, peripheral lymphadenopathy or hepatospenomegaly, with the insidious onset of respiratory difficulties or constitutional symptoms (fever, night sweats, weight loss), or with an acute onset accompanied by fever, erythema nodosum and polyarthritis.

Hypercalcemia and small lytic lesions in bones, particularly of the hand, may be observed.

Diagnosis of sarcoidosis is one of exclusion of other similar diseases with non-caseating granulomas (Eg. tuberculosis, berylliosis, fungal infections).

Clinically, the lesion is slowly progressive, pursue a remitting or resolving course and spontaneously resolved (with or without steroid therapy).

Most patient with sarcoidosis respond well to treatment with corticosteroids or spontaneously remit.

However, some progress to end stage lung disease with honeycombing.

In 65 to 70 % of patients, there are no or only minimal residual manifestations, 20 % have permanent lung or ocular dysfunction, and 10 % die, primarily from progressive pulmonary fibrosis and cor pulmonale.

 Laboratory tests used to diagnose sarcoidosis include subcutaneous injection of Kveim antigen (an extract of spleen from a patient with sarcoidosis) and measurements of the serum level of angiotensin converting enzyme.

About 6 weeks after injection of the Kveim antigen, an indurated granulomatous nodule appears in the skin.

The test is seldom used , since the material is scarce.

It is also derived from human material and may therefore by hazardous.

It is now apparent that the raised serum angiotensin converting enzyme is nonspecific and may occur in many interstitial lung diseases.

 However it is useful for monitoring the activity of sarcoidosis and the effects of treatment.

Most physicians now use bronchoalveolar lavage to monitor the cell content.

The most reliable procedure for the diagnosis of sarcoidosis is transbronchial lung biopsy, a procedure in which lung tissue is obtained through a fiberoptic  bronchoscope.

Occasionally, biopsy of a mediastinal lymph node by mediastinoscopy is diagnostic.