The perfusion lung scan was of substantial clinical utility in our setting; 36 percent of patients referred with suspected pulmonary embolism had normal lung scans. These patients were spared further investigation and treatment for venous thromboembolism. The frequency of normal perfusion scans in patients with suspected pulmonary embolism ranges from 13 to 49 percent. The utility of perfusion scanning therefore depends on the clinical setting.

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The results indicate that patients with suspected pulmonary embolism and a normal perfusion lung scan have an excellent prognosis without anticoagulant therapy. Symptomatic venous thromboembolism was rare on follow-up in our patients with normal perfusion scans (0.6 percent [three of 515 patients]). Further, two of the three patients with venous thromboembo­lism on follow-up had predisposing factors which placed them at continued risk for venous thrombo­embolism. The results on follow-up indicate that a normal perfusion scan excludes clinically important pulmonary embolism. Our findings support and ex­tend the observations of Kipper et al who reported pulmonary embolism on follow-up in only one of 68 patients with suspected pulmonary embolism and normal perfusion scans.

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Patients

The 515 consecutive patients with clinically sus­pected pulmonary embolism and normal perfusion scans ranged in age from 14 to 93 years (mean, 45 years); 154 (30 percent) were men and 361 (70 percent) were women. Their clinical characteristics are shown in Table 1. Of the 515 patients, 361 patients (70 percent) were outpatients at the time of presentation and 154 (30 percent) were inpatients.

Findings by Impedance Plethysmography at Presentation

Impedance plethysmography was performed suc­cessfully in 493 of the 515 patients (it could not be performed in 22 patients due to leg casts, leg ampu­tation or other reasons). Proximal-vein thrombosis was detected by impedance plethysmography in only five of the 493 patients (1 percent). Of the five patients, venography confirmed proximal-vein thrombosis in three patients, was unsuccessful in one patient and could not be performed in the remaining patient who could not be moved from intensive care.

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Rtiients

Between 1981 and 1988,1,420 consecutive patients with clinically suspected pulmonary embolism were referred to the Thromboem­bolism Service at Chedoke-McMaster Hospitals and were studied prospectively. The 515 (36 percent) of these patients who had normal perfusion lung scans are the subject of this report. The findings in the patients with abnormal perfusion scans have been described previously.

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The perfusion lung scan is a pivotal test in the diagnosis of pulmonary embolism. In this test, which reflects the relative distribution of pulmonary blood flow, intravenously injected particles of radio­active macroaggregated albumin lodge in the pulmo­nary microcirculation. The distribution of these par­ticles is measured by scanning the chest with a gamma camera in several projections. Studies in experimental animal models indicate that this technique detects 97 percent of occlusive emboli larger than 2 mm in diameter, but may fail to detect smaller pulmonary emboli or incompletely occlusive emboli.

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Until now, more than 20 reports involving PXE have been published in Korea, most of which present cases with typical clinical symptoms, asso¬ciated systemic abnormalities, or perforating PXE. Unlike previous reports, our patient complained of severe pruritus on a normal appearing chin without other systemic problems or a family history. Recently, Lebwohl et al reported a previously unde- scribed cutaneous finding in a patient with PXE. As a marker of PXE, mental creases are sensitive and highly specific under the age of 30 years, affecting two-thirds of patients, but not in age-matched control patients. However, there was no further description of clinical findings related to PXE. Our patient also had horizontal and oblique mental creases; however, the creases may not be specific because the development of a horizontal mental crease is not rare in individuals with advanced age. Taylor et al reported tumefactive lipedema with PXE-like microscopic changes. The patient could have either a subclinical form of PXE, perhaps predisposing to lipedema, or secondary elastic tissue changes resulting from the massive edema. They explained if the latter was the case, this could represent an unusual manifestation of localized acquired cutaneous PXE. Similarly, there is a possibility that PXE-like changes in our case might be secondary changes resulting from the scratching.

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PXE is a rare, genetic disorder primarily affecting the skin, eyes, and cardiovascular system. The inheritance is usually autosomal recessive, but may be autosomal dominant or sporadic. Cutaneous lesions usually occur in the second or third decade of life. However, the presence of cutaneous lesions is usually not noted until adolescence or even later adulthood because of the asymptomatic nature. The primary skin lesions are small, yellowish papules in a linear or reticular pattern, tending to gradually coalesce to form plaques giving the skin a “plucked chicken” appearance. A skin biopsy specimen is mandatory for the diagnosis of PXE to demonstrate the cardinal histologic features. PXE is characterized by degenerative changes affecting the elastic fibers of the mid-dermis. The elastic fibers are readily identifiable with hematoxylin and eosin (H&E) staining and are rather basophilic and irregular, appearing as widely dispersed granular material amidst normal collagen fibers. Fibers stain positively with the von Kossa technique, confirming the presence of calcium and phosphorous. In our case, there was no distinct skin finding, except the severe itching sensation localized to the chin of about 10 years duration. She did not have a family history of PXE. She was 60 years of age at that time of the skin biopsy, which showed PXE-like histologic changes, although she had unusual clinical features. Solar elastosis, which also exhibits abnormal elastic tissue, was easily excluded because in solar elastosis the material is located in the upper dermis and presents as dense masses rather than individual altered fibers. Moreover, these dense masses always stain negative for calcium.

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