Sonographic quantification of the type IV reaction after intradermal application of recall antigens

20-MHz B-scan high-resolution sonography permits non-invasive, two-dimensional visualisation of micromorphological structures in vivo, and allows precise measurement of the depth and extent of inflammatory skin lesions. In 50 patients, the reactions following intradermal application of 8 recall antigens to the volar forearm were evaluated clinically and sonographically at various times (0, 24, 48, 72 h). In 30 patients, one of the inflammatory papules was excised after 48 h for complete histological work-up (serial sections) and subsequent comparison with the sonographic image. Infiltrates were characterised in the ultrasound scans by the almost regular occurrence of convexity of the skin surface, by a loosened structure (loss of echogenicity) of the corium and by protrusion of the corium into the subcutaneous fatty tissue. It was also possible to follow the dynamics of the type IV reaction with the measurement of echogenicity (densitometry). High-frequency ultrasound is an objective, exact and very sensitive tool for the measurement of type IV reactions after intradermal application of recall antigens and therefore superior to clinical evaluation. The B-scan was superior to the A-scan. However, for routine evaluation of tuberculin-like reactions, sonography is too time-consuming. Our results suggest that densitometry provides no additional or necessary information compared to sonometry.