De Quervain's disease. An ultrastructural study.

The tendon sheaths of extensor pollicis brevis (EPB) and abductor pollicis longus (APL), obtained from four patients with de Quervain's disease were studied by light and electron microscopy. Three different layers were identified in the sheath which was much thicker than normal. Both the outer and the middle layers had thick bundles of collagen fibres with scattered fibroblasts. The inner layer was mainly formed by chondroid and myxomatous tissue. Collagen fibrils were thicker than normal, reaching 2100 nm in diameter. Numerous cells which resembled "myofibroblasts" were scattered throughout the whole thickness of the sheath. The results seem to indicate that thickening and hardening of the EPB and APL tendon sheaths in de Quervain's disease is caused by increased synthesis of the extracellular matrix, increased thickness of the collagen fibrils and areas of myxomatous and chondroid metaplasia.