Digital Clubbing

Aka: Digital Clubbing, Clubbing, Schamroth's Window Test, Schamroth's Sign, Digital Index, Lovibond Angle

1. See Also
   1. Fingernail
   2. Nail Abnormality
   3. Hypertrophic Osteoarthropathy
2. History
   1. First described by Hippocrates in 5th century B.C.
3. Definition
   1. Bulbous digital deformity
   2. Watch-crystal deformity of Fingernail
4. Pathophysiology
   1. Sign of Hypertrophic Osteoarthropathy (Acropachy)
   2. Thickening of nail bed's soft tissue (especially proximally)
      1. Typically affects all fingers
   3. Results from abnormal microvasculature with increased blood flow to the microvasculature
5. Signs: Schamroth's Window Test for Clubbing
   1. Oppose fingers of both hands
   2. Observe space formed between nail bases
      1. Normal: Diamond-Shaped "window" seen
      2. Clubbing:
         1. Window erased
         2. V-shaped gap at distal end of nail is wider
6. Signs: Digital Index
   1. Use non-elastic string to measure digit circumference
   2. Measure circumference at 2 sites on all 10 digits
      1. Nailbed circumference (NB)
      2. Distal interphalangeal joint circumference (DIP)
   3. Calculate NB/DIP ratio
   4. Results suggestive of Digital Clubbing
      1. NB/DIP ratio exceeds 1 on all fingers or
      2. Sum of all ten NB/DIP ratios >10
7. Signs: Lovibond Angle
   1. Line 1
      1. Draw a longitudinal line across the top of the distal digit soft tissue
   2. Line 2
      1. Draw a longitudinal line across the midpoint of the nail plate
   3. Angle
      1. Measure the angle at the intersection of the 2 lines (clockwise from proximal end of line 1)
   4. Interpretation
      1. Angle greater than 180 degrees is suggestive of Clubbing
8. Causes
   1. See Hypertrophic Osteoarthropathy Causes (Clubbing Causes)
9. References
   1. Vazquez-Abad (1989) J Rheumatol 16:1518-20