Applied Radiology

Patients with SM typically present with a constellation of signs andsymptoms that vary considerably from individual to individual. Theheterogeneous manifestations of this disease reflect both the ubiquitous natureof mast cells in the body and the numerous mast cell mediators and theireffects. Cutaneous signs often appear first and usually are consistent withurticaria pigmentosa (figure 1); patients present with complaints of pruritisand flushing, and a skin biopsy will reveal an increase in the number of mastcells in the dermis. Hyperpigmented lesions that exhibit the "wheal andflare" reaction when disturbed also are a common dermatologic sign.Complaints of nausea, diarrhea, and vomiting indicate gastrointestinalinvolvement. An increased number of mast cells in the bones will be manifestedby symptoms of bone and joint pain.

Radiographic findings can be helpful in the diagnosis of SM and also intracking the progression of the disease. A cardinal sign of SM is the presenceof osteoporosis and osteosclerosis in the skeletal system. These dichotomoussigns can appear in both the axial and apendicular skeleton and can be due to avariety of different mechanisms. Heparin and prostaglandins released by themast cells activate osteoclasts to reabsorb bone, a process which can progressto osteoporosis.1 Figure 2 demonstrates the possibility of tibial involvement.In this instance, the decrease in bone density is particularly prominent in thecortices, and-as often seen in osteoporosis-there has been anincrease in the medullary cavity without change in the diameter of the boneshaft. Conversely, histamine released by mast cells promotes osteoblasticactivity, leading to osteosclerosis; such sclerosis can be diffuse or focal(figure 3) in distribution. Although the figures seen here may suggest thatareas of increased bone density are segregated from areas of osteopenia, thesetwo pathological changes in bone can coexist in adjacent areas. In figure 4,the lower vertebrae have diffuse osteosclerosis, while the upper vertebraeexhibit signs of osteoporosis.

Gastrointestinal manifestations of SM are diverse and can be visualizedusing a variety of radiographic techniques. Avila et al used CT and ultrasoundto demonstrate such common abdominal imaging findings associated with systemicmastocytosis as hepatomegaly, retroperitoneal adenopathy, periportaladenopathy, mesenteric adenopathy, thickening of the omentum and the mesentery,and ascites.2

Barium GI study may be useful in revealing additional evidence of GIinvolvement. The presence of thickened, nodular irregular folds in the smallbowel often are seen with SM (figure 5). This sign may reflect mast cellinfiltration of the lamina propria, although some studies have showed thatbiopsies of such nodules predominantly revealed lymphocytes and plasma cells,and showed few mast cells.3 Because histamine released by mast cells can causean increase in gastric acid secretion, ulcers develop in many patients with SM(figure 6).

It is important to recognize that, individually, most of these radiographicsigns are not specific to mastocytosis. That is, taken alone, the interplay ofosteoporosis and osteosclerosis in the skeletal system could easily beindicative of mixed metastatic disease instead of mastocytosis; the duodenalulcer could just as likely be due to Helicobacter pylori infection as it is toexcessive histamine-stimulated gastric acid secretion. It is the completeconstellation of signs in the patients presented here that gave a clue to thediagnosis of SM. However, as this full array of radiographic signs may not bepresent in all SM patients, additional studies such as skin biopsies often arenecessary to complete the diagnosis.

References

This series of diagnostic challenges is prepared by David J. Sartoris, MD,

Professor, Department of Radiology, University of California School ofMedicine, San Diego, CA.