Proportion of palpable nodules by age

On average, about one third of the nodules can be found by palpation. Diagnosis by palpation, however, must be judged age-dependently. The proportion of palpable nodules is very low in children and increases to about 30% in 10 year old children and to about 40% in aged people. The estimates differ considerably between villages, showing strong observer variability (graph below). Palpation of a patient
Palpation of a patient
Source: WHO/TDR
Proportion of palpable nodules by age Inter-individual heterogeneity in the probability to palpate a nodule clearly challenges the usefulness of palpation on the level of the individual patient. E.g., in 20 year old patients, the median value is 20% and the region of tolerance (range between quantiles 2.5% and 97.5%) runs from 0% to 92% (lower graph).



Figure: The proportion of palpable nodules by age. Curves in the grey part of both graphs result from extrapolation of the simulation results.

A: Expected proportion of palpable nodules among the 14 West African villages. The grey curve represents the common estimate for all 2560 inhabitants in the 14 villages.

B: Common distribution, represented by quantiles. The region of tolerance, in which the central 95% of observations are expected, is delimited by dashed lines. (Source: Duerr et al., 2008)
Related pages: Nodules, Diagnosis by palpation of nodules, Diagnostic value of nodule palpation.

Further reading: Duerr HP, Raddatz G, Eichner M. Diagnostic value of nodule palpation in onchocerciasis. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2008;102(2):148-154.