Castell's Sign - Interpretation

Interpretation

The 1993 systematic review by the Rational Clinical Examination found that Castell’s sign was the most sensitive physical examination maneuver for detecting splenomegaly when comparing palpation, Nixon’s sign (another percussion sign), and Traube's space percussion:

• sensitivity = 82%
• specificity = 83%

In asymptomatic patients where there is a very low clinical suspicion for splenomegaly, physical examination alone is unlikely to rule-in splenomegaly due to the inadequate sensitivity of the examination. Similar to many other findings in medicine, Castell’s sign must be combined with clinical findings to rule in splenomegaly. To achieve a positive predictive value over 90%, the pretest probability must be 70%. Grover et al., recommends a greater than 10% preexamination clinical suspicion of splenic enlargement to effectively rule in the diagnosis of splenomegaly with physical exam. However, a 10% pretest probabilibity only yields a positive predictive value of 35%.

To rule out an enlarged spleen, a pretest probability of 30% or less will yield a negative predictive value over 90% (calculation)

Given the paucity of physical exam findings to evaluate possible splenomegaly, Castell’s sign is the most sensitive, and is thus a good tool to teach in an advanced-type physical diagnosis course. Castell’s has been shown to be superior in sensitivity to other spleen percussion signs as well as palpation, which is not likely useful due to the extreme enlargement necessary to feel the spleen below the costal margin. Castell’s sign is thus, in the appropriate clinical scenario, an important part of the abdominal physical exam.