The opposable thumb is said to be one of the key features that distinguishes humans from much of the animal world. Not all primates have an opposable thumb; only Old World monkeys and apes have this unique adaptation.
The thumb is powered by numerous muscles. Two muscles contribute to the motion of radial abduction- the extensor pollicis brevis (EPB) and abductor pollicis longus (APL). The tendons for these muscles pass through the first dorsal compartment of the wrist, where they are surrounded by tendon sheaths. Inflammation of these tendon sheaths was first described by the Swiss surgeon Fritz de Quervain in 1895, who also described an inflammatory condition of the thyroid gland ("de Quervain thyroiditis")
In this case, a 36 year-old woman presented with wrist pain. Radiographs were obtained, and an erosion was noted at the base of the radial styloid, along with adjacent soft tissue calcification. There was some concern that this could represent a soft-tissue mass, and the patient was referred for an MRI. Coronal intermediate weighted image reveals the erosion (red arrow) at the base of the radial styloid:
A coronal gradient echo image again depicts the erosion (red arrow), and a fleck of soft tissue calcification (yellow arrow):
Chien et al. described focal radiographic abnormalities of the radial styloid as a manifestation of de Quervain disease (AJR 177:1383-1386, 2001). Axial images from our patient:
(A) Axial T1 image depicts erosion in distal radius. (B) Axial T2 fatsat image shows inflammation surrounding the APL and EPB tendons (green arrow).
Chein et al. noted that "in the appropriate clinical context, radiographic visualization of focal cortical erosion, sclerosis, or periosteal bone apposition of the radial styloid should suggest the diagnosis of de Quervain tenosynovitis". Although their report described the x-ray manifestations of de Quervain syndrome, the same findings can be depicted on MRI, as demonstrated in this case.
Vic David MD