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Epidemiology
The true prevalence of sarcoidosis is difficult to determine because the disease is often asymptomatic and frequently does not come to medical attention (3). Sarcoidosis typically manifests in the 3rd or 4th decades of life, although the age range of patients extends from preadolescence to the 7th decade (3).
It is found with varying frequency in virtually every country of the world. There is a higher prevalence in countries with temperate climates (United States [10-40 cases/100,000], United Kingdom [20-30 cases/100,000], Scandinavia [10-20 cases/100,000], Japan [10-20 cases/100,000]) than in those in tropical regions (Africa, southeast Asia, India, Central and South America [<10 cases/100,000]) (4).
Different races are also affected to varying degrees. Sarcoidosis is rarely seen in African or South American blacks, but the prevalence in African-Americans (80 cases/100,000 in New York City) is ten times higher than in American whites. Female predominance in the United States has been noted only in the black population (4). Extrathoracic manifestations of sarcoidosis occur more frequently in black patients (5).
Signs and Symptoms
Approximately 50% of patients with sarcoidosis are asymptomatic at diagnosis, 25% complain of cough or dyspnea, and 25% have extrathoracic symptoms, usually related to the skin or eyes. Constitutional symptoms of fatigue, weight loss, and fever occur less commonly (3).
Ten percent to 30% of patients develop skin lesions, including erythema nodosum, lupus pernio, or skin plaques or scars (3,5,6,7). Erythema nodosum is characterized by multiple, bilateral, tender erythematous nodules occurring mostly on the anterior aspect of the lower extremities (Figure 1a). There is wide variability in its prevalence in different populations of patients with sarcoidosis (10% or less in America, 30% in Europe). It has a predilection for female patients, particularly those of Scandinavian, Irish, or Puerto Rican origin. Lupus pernio is a specific form of cutaneous sarcoidosis. It is characterized by indurated, bluish-purple elevations, affecting mainly the nose and digits (Figure 1b). It is typically seen in African-Americans and is associated with involvement of the upper respiratory tract (3).
Löfgren syndrome is a specific clinical manifestation of sarcoidosis. It is an acute febrile illness accompanied by erythema nodosum, hilar adenopathy, malaise, arthritis, and occasionally uveitis and parotitis (6). Recognition of these associated signs is important because it may allow the presumptive diagnosis of sarcoidosis.
Five percent of patients with sarcoidosis present with eye symptoms such as injection, photophobia, unilateral or bilateral blurred vision, and occasionally glaucoma. The uveal tract is most commonly involved, but retinal, scleral, and conjunctival involvement may also occur. The lacrimal and salivary glands may be involved, even in the absence of ocular lesions. Twenty-five percent of patients will have eye involvement by sarcoidosis at some time during the course of the disease (3,6,7).
Laboratory Findings
The immunologic imbalance in sarcoidosis may manifest clinically as anergy. Although cell-mediated immunity is enhanced at sites of disease activity, it is depressed systemically. Patients may also exhibit hypergammaglobulinemia caused by T-cell lymphokine stimulation of B lymphocytes. Angiotensin-converting enzyme is elevated in the serum and may correlate with disease activity. Angiotensin-converting enzyme is a product of macrophages and is therefore an indicator of granuloma burden in the body (5). Hypercalcemia and hypercalciuria are due to hydroxylation of, 25-dihydroxy vitamin D in macrophages, which results in increased intestinal absorption of calcium. Persistent hypercalcemia can lead to nephrocalcinosis (5,6).
Pulmonary Function Findings
In the acute form of sarcoidosis, there may be no functional impairment; however, if the disease progresses, pulmonary physiologic findings may indicate restrictive as well as obstructive airway disease. Low lung compliance results from diffuse interstitial disease. Generalized reduction in volume throughout all lobes and segments is reflected in decreased vital capacity, decreased residual volume, and decreased total lung capacity. These findings indicate restrictive lung disease. When present, endobronchial lesions or peribronchial fibrosis may produce features of superimposed obstructive airway disease. This results in a decreased flow rate caused by increased airway resistance (3,7,8,9).
Clinical Features