**2.2 Cardiopulmonary and laboratory tests**

Pulmonary function tests are also routinely used in sarcoidosis for early diagnosis and follow-up. They include the evaluation of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), the total lung capacity determination (TLC), vital capacity (VC), residual volume (RV) associated with body

plethysmography, and a carbon monoxide diffusion capacity test of the lungs for carbon monoxide (DLCO).

Sarcoidosis is commonly considered a restrictive disorder, but more recent studies are demonstrating some opposite results.

Restrictive disorders (infiltrative) are characterized by a reduction in lung volume, with difficult in taking air inside the lungs and decreased total lung capacity. Other restrictive disorders are chest wall disorders (neuromuscular, e.g., polio, kyphoscoliosis, pleural disease, and severe obesity); chronic interstitial and infiltrative disease (pulmonary fibrosis, pneumoconioses, granulomatous diseases, pulmonary eosinophilia, and pulmonary alveolar proteinosis); Acute diseases (ARDS and infections).

Typical symptoms are dyspnea, tachypnea, end inspiratory crackles without airway obstruction, honey-comb lung, secondary pulmonary hypertension, and cor pulmonale.

In restrictive pulmonary disease, lung volume is decrease, but flow rate is normal as follows:


Usually, a significant correlation between radiological stage and pulmonary function tests is found.

Cardiopulmonary exercise testing (CPET) is another useful tool to identify and quantify the extent of pulmonary involvement and also may suggest cardiac involvement that otherwise is not evident [2]. It provides an integrative assessment of involving the pulmonary, cardiovascular, muscular, and cellular oxidative systems and involves measurements of gas exchange as follows:


In patients who have normal gas exchange at rest, CPET unmasks the gas exchange abnormalities.

Laboratory tests can identify some serum abnormalities as high blood calcium with a normal parathyroid hormone level and hypercalciuria, or elevated levels of angiotensin converting enzyme (ACE) in the blood [1].

**35**

*Early Diagnosis of Sarcoidosis*

**2.3 FDG-PET**

tion on PET imaging.

several years [3].

monitoring the sarcoidosis activity [6].

*DOI: http://dx.doi.org/10.5772/intechopen.90523*

FDG-PET is a metabolic imaging technique and provides an insight into metabolism of this disease. It relies on the principle of increased accumulation and metabolism of glucose by the malignant or inflammatory areas. FDG is a radioactive analog of glucose that enters cells through the same receptors that are involved in glucose uptake and gets converted into FDG 6 phosphate by the enzyme hexokinase, similar to glucose metabolism by the glycolytic pathway. FDG 6 phosphate is not metabolized further and gets entrapped in the cell. Tissues with high glucose metabolism such as brain tissue gray matter, cancer cells, and inflammatory changes show increased fluorine – 18 fluorodeoxyglucose ((18) F-FDG) accumula-

As a key component of the inflammatory process, inflammatory cells consume glucose at a much higher level than peripheral noninflammatory cells, leading to higher glucose metabolism and increased uptake of (18) F-FDG within inflammatory foci. Therefore, the level of FDG uptake is proportional to the level of glycolysis in the tissue. This explains the mechanism of increased uptake of FDG in

The role of fluoro-deoxy glucose-positron emission tomography (FDG-PET) scanning in assessing the extent of disease spread or metastasis and its utility in assessing response to treatment in the form of chemotherapy or radiotherapy is well defined in many neoplastic conditions, and its utility has also been recognized in

During the last years, FDG-PET imaging has been shown to have a central role to detect inflammation activity and has become a novel fundamental tool, playing also an increasingly important role in the management of patients with any inflammatory conditions. FDG-PET can afford precious information in patients with pulmonary and extrapulmonary sarcoidosis and has become a centerpiece for testing the efficacy of different therapies [5]. In difficult clinical cases, it can also be useful to plan the site of biopsy in order to determinate a histopathological diagnosis.

A combined modality using FDG-PET and CT scanning (FDG-PET/CT) has been found to be more sensitive than PET in diagnosing. FDG-PET and a combination of this procedure with computed tomography scanning (FDG-PET/CT) has gained prominent attention in patients with sarcoidosis over the last two decades as a means to assess disease activity and response to therapy. Radionuclide imaging techniques have increasingly been used in the evaluation of organ involvement in sarcoidosis. F-FDG-PET/CT scanning has received increasing attention in last

The usefulness of F-FDG-PET/CT is to identify the disease activity and the extent of organ involvement in patients affected by sarcoidosis; F-FDG-PET/CT is still useful to determinate its utility in the evaluation of response to drug treatment, comparing the agreement between clinical, radiological (with chest radiography and/or HRCT of lungs), and metabolic indices (FDG-PET/CT) of disease activity. *Monitoring disease activity* in sarcoidosis still remains a clinical goal as there is no gold standard. The term "activity" in sarcoidosis means ongoing inflammation that necessitates appropriate drug therapy [3]. PET imaging is a new tool to assess the metabolic activity, but there is still limited data on the role of serial PET scans in

*Conventional imaging techniques* used in sarcoidosis are chest radiography and CT. Even though chest radiography and HR-CT are still the fundamental for diagnosing pulmonary involvement, F- FDG PET appears to be superior to both techniques to identify active sites of disease. F- FDG- PET also correlates well with serum biomarkers, such as soluble interleukin-2 receptor in symptomatic patients,

malignancy, inflammatory, and infectious processes [3].

certain inflammatory conditions, like sarcoidosis.
