Definition and general characteristics of the disease
Sarcoidosis is a systemic inflammatory disease of unknown etiology characterized by the formation of non-caseating granulomas, multisystem involvement of various organs, and T-cell activation at the site of granulomatous inflammation. Although mediastinal and pulmonary lymph node involvement is most common, the disease can manifest as lesions of the skin, heart, nervous system (neurosarcoidosis), joints, visual organs, and other systems.
The only criterion for establishing the diagnosis is histological verification following a biopsy. All other data—clinical, laboratory, and imaging—merely allow the physician to suspect the disease and direct further diagnostic workup.
Clinical presentation and physical examination
Clinical manifestations of sarcoidosis are variable and depend on the affected system. Some patients are asymptomatic, and the disease is discovered incidentally during routine fluorography or chest radiography.
During the physical examination, attention should be paid to:
- the condition of the skin, scars, and tattoos (reactivation in the scar area is possible);
- the presence of erythema nodosum and subcutaneous nodules—Darier–Roussy sarcoids, which are frequently tender upon palpation;
- joint status when joint involvement is suspected;
- eye examination—an ophthalmologist consultation is required to rule out uveitis.
Diagnostic radiology
Imaging modalities are key for suspecting and staging the disease. The initial finding is most commonly enlarged intrathoracic lymph nodes detected on fluorography or radiography.
- High-resolution computed tomography (HRCT) is the primary method that allows simultaneous assessment of the mediastinal lymph nodes and lung parenchyma. With the introduction of HRCT, the detection rate of combined lymph node and pulmonary tissue involvement has significantly increased.
- MRI is used when neurosarcoidosis and cardiac sarcoidosis are suspected.
- Ultrasound of various localizations.
- PET-CT to assess disease activity and search for extrathoracic lesions.
- Perfusion lung scintigraphy.
Laboratory diagnostics
There are no specific laboratory markers capable of confirming or ruling out sarcoidosis. Laboratory findings play an ancillary role and are evaluated as either "for" or "against" the diagnosis.
- Complete blood count—elevated ESR, lymphopenia, and monocytosis may occur; a normal blood count does not rule out the disease.
- Serum calcium and 24-hour urinary calcium levels (hypercalcemia and hypercalciuria are characteristic).
- Angiotensin-converting enzyme (ACE) activity.
- ALT, AST activity, and creatinine levels to assess liver and kidney involvement.
- Intradermal tests (Mantoux test, Diaskintest) and a phthisiatrician consultation are mandatory for differential diagnosis with tuberculosis.
Invasive diagnostics and biopsy
Invasive methods are divided into bronchoscopic and surgical. In modern practice, preference is given to less traumatic bronchoscopic techniques.
- Bronchoalveolar lavage with cytological analysis.
- Transbronchial lung biopsy.
- Transbronchial cryobiopsy is a highly informative modern verification method.
- CT-guided transthoracic needle biopsy.
- Video-assisted thoracoscopic surgery (VATS) biopsy of the lung and intrathoracic lymph nodes.
- Open biopsy (thoracotomy) is used extremely rarely due to higher invasiveness.
Morphological verification
The morphological substrate of sarcoidosis is an epithelioid cell granuloma without caseous necrosis. The pathomorphologist describes a compact accumulation of mononuclear phagocytes, lymphocytes, and granulocytes. Typical localization is subpleural and peribronchovascular.
In the center of the granuloma are epithelioid cells and Pirogov–Langhans giant multinucleated cells with a characteristic peripheral arrangement of nuclei. A lymphocytic rim surrounds the periphery. In some cases, the morphological picture may present as lymphocytic alveolitis with inflammatory infiltration of the pulmonary interstitium without formed granulomas.
Sarcoidosis is referred to as the "great imitator": no imaging or laboratory method can definitively confirm the diagnosis without morphological examination. Exceptions include situations where a biopsy is impossible due to the patient's critical condition or refusal of invasive intervention.
Key points
- Sarcoidosis is a systemic granulomatous disease of unknown etiology with multiorgan involvement.
- The only criterion for establishing the diagnosis is histological verification of the epithelioid cell granuloma.
- The disease is often detected incidentally during fluorography due to enlarged intrathoracic lymph nodes.
- High-resolution CT is the main imaging modality for diagnosis and staging.
- Laboratory parameters (ACE, calcium, ESR) play only an ancillary role.
- Differential diagnosis with tuberculosis is mandatory: Mantoux test, Diaskintest, phthisiatrician consultation.
- The modern trend is a shift from surgical to bronchoscopic biopsy methods, including transbronchial cryobiopsy.
- Morphological feature: non-caseating granuloma with Pirogov–Langhans giant cells.