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Point-of-Care Ultrasound for the Assessment of Digital Clubbing

(A) The hand is placed inside a clear plastic container filled with water with the wrist resting on the edge of the container. With a high-frequency linear transducer and gel, a longitudinal axis view of the digit of interest is obtained, using the container as an anchor to stabilize the transducer. (B) Clubbed fingers (D2 = index, D3 = middle) viewed in profile. (C) Ultrasound image of the patient’s clubbed middle finger (D3) in the longitudinal plane. Profile angle (ABC) and hyponychial angle (ABD) are increased at 187° and 195°, respectively. (D) Ultrasound image of a middle finger of a healthy control in the longitudinal plane. Normal profile angle (ABC) and hyponychial angle (ABD) are demonstrated at 169° and 180°, respectively.

 

Digital clubbing, a resultant finding from the proliferation of connective tissue in the terminal portion of fingers or toes, has long been recognized as a sign for a number of underlying infectious, inflammatory, malignant, and vascular conditions.1 A profile angle >176° and a hyponychial angle >192° support the diagnosis of clubbing.1Quantification of these angles can be done using plaster casts, shadowgraphs, planimeters, or digital photography—techniques that are cumbersome.2 Practically speaking, physicians commonly rely on subjective assessments at the bedside.3 The increasing availability of point-of-care ultrasound (POCUS) as an adjunct to physical examination warrants a description of its use to facilitate the quantification of the profile and hyponychial angles at the bedside.

Case Report

A 42-year-old woman with a 10-year history of pulmonary alveolar proteinosis was admitted to the hospital with abdominal pain. On physical examination, she was subjectively noted to have clubbing. A technique using POCUS was employed to confirm this finding. Using the lateral water bath approach,4 the patient’s hand was placed into a clear plastic basin filled with water, and a longitudinal view of the digit was obtained with a 14-5 MHz linear transducer (SonixTouch; BK Ultrasound, Peabody, Mass) (Figure,, A). The ultrasound images are able to demonstrate the abnormal nail-fold angles (Figure,, B and C) compared with a healthy control (Figure,, D). By downloading these images and using an on-screen protractor, the patient’s profile angle could be measured at 187° and the hyponychial angle at 195° compared with control angles of 169° and 180°, respectively.

Discussion

A profile angle >176° and a hyponychial angle >192° are considered abnormal.1 At the bedside, the subjective determination of the presence of clubbing generally showed only fair inter-rater agreement.1 A rapid, objective bedside method may assist in better quantifying these angles. We have demonstrated a simple method for angle quantification using POCUS. Digital photography can also be used to quantify angles (Figure,, B); however, the sonographic rendering of the nail bed, nail, and underlying phalanx as bright echogenic structures makes the angles easier to quantify.

Using ultrasound to assess for clubbing has been described previously, whereby the patient immerses his or her hand in a basin of water and a high-frequency transducer is placed above the hand and imaged through the water. However, without any physical anchoring,5 this technique may be limited by movement artifacts. By using the lateral water bath technique,4 the imaging technique is easier for learners to perform and may allow for the acquisition of higher-quality images that can be used for confirmation of clinical findings, as well as for bedside teaching.

Conclusions

Ultrasound is a valuable clinical adjunct to the traditional physical examination for the assessment of digital clubbing. Using a lateral water bath technique with a high-frequency transducer, longitudinal images of the distal phalange can assist in the quantification of the profile and hyponychial angles.

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-Inka Toman, MD, MSc, Peter Rye, MD, Janeve Desy, MD, Irene W.Y. Ma, MD, PhD, RDMS, RDCS

This article originally appeared in the November issue of The American Journal of Medicine.

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