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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 (upper graph).
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).
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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., 2007)
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Related pages:
Nodules,
Diagnosis by palpation of nodules,
Diagnostic value of nodule palpation.
Further reading:
Duerr HP, Raddatz G, Eichner M, 2007.
Diagnostic value of nodule palpation in onchocerciasis.
Transactions of the Royal Society of Tropical Medicine and Hygiene.
In press.
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