Diagnosing onchocerciasis by palpation of nodules

Boy with palapable nodule
Boy with palpable nodule
Source: WHO/TDR
The parasite Onchocerca volvulus aggregates within subdermal nodules which can be palpated. Diagnosis by palpating nodules, however, is uncertain because nodules may be very small, located in deeper layers of the skin, etc. Diagnostic measures are difficult to derive and depend on the age of the patients. Is diagnosis by palpation sufficiently reliable to support epidemiological decision making?
The sensitivity of nodule palpation depends on the parasite burden, because a patient with many nodules is more likely to be found "positive" than a patient with few nodules. How can we determine the sensitivity of nodule palpation when at the same time exactly this depends on knowing how many nodules a patient harbours? More... Diagnostic measures
Data on nodule palpation show that the diagnosis strongly depends on the age of a patient. It is important to look at the proportions of true-positive, false-positive, false-negative and true-negative diagnoses. More... Palpation diagnosis by age
Compiling the information on sensitivity, specifity, and the true and the negative predictive value allows for predicting the true prevalence of onchocerciasis from a prevalence which has been determined by palpation. However, it turns out that only slight insights can be gained through nodule palpation. More... Diagnostic value of palpation