SAN FRANCISCO - Lymphangioleiomyomatosis (LAM) is a giant word for medical enigma. A rare multisystem disorder that strikes only young and middle-aged women, LAM is characterized by the proliferation of abnormal smooth muscle cells in the lungs and the lymphatics of the thorax and retroperitoneum, and by the formation of pulmonary cysts that progressively replace the lung parenchyma.
LAM has no known cause or cure, no common environmental or genetic factors, no known clusters, and no treatment that's helped all of those who suffer from it. LAM isn't cancer, but it can proliferate as aggressively. Without lung transplant surgery, those with advanced disease can die of respiratory failure.
Fortunately, CT is beginning to shed light on LAM. In a poster presentation Tuesday at the American Thoracic Society meeting in San Francisco, Drs. Nilo Avila, Andrew Dwyer, and colleagues from the National Institutes of Health in Bethesda, MD, explained CT's role in diagnosing and assessing the disorder. Dr. Avila was on hand to discuss the study with AuntMinnie.com.
"In the lungs, you have cysts; the cysts can rupture and you have pneumothorax," Avila said. "That's actually the most common presentation. Some patients go misdiagnosed for years, or are diagnosed with pneumothorax -- and the most common cause of pneumothorax is just spontaneous. The other thing they get is fluid in the lungs -- chylus -- a fatty substance produced by the lymph system. When that spills, it can also cause symptoms, so because of those two problems they present."
Other symptoms include bloating, abdominal discomfort, increasing abdominal girth, edema of the lower extremities, parathesias, nocturia, incontinence, and labial swelling.
To assess the spectrum and prevalence of LAM in patients diagnosed with the disease, Avila's team evaluated 166 women using high-resolution CT of the chest, and conventional CT of the abdomen and pelvis. Images were acquired on a HiSpeed single-slice CT scanner (GE Medical Systems, Waukesha, WI) following injection of 130 cc of nonionic contrast solution. A sampling protocol was used to acquire the chest images. The researchers acquired continuous 1-mm-thick slices over 1 cm, skipped 3 cm, then repeated the process, Avila said.
The lung cysts are visualized as "black holes" on CT, Avila said. They are uniformly arranged, and vary from 1 mm to several centimeters in diameter.
The study grouped patients according to the severity of pulmonary disease, i.e., the extent of lung involvement with parenchymal cysts. Thirty-one percent of patients had grade 1 disease (< 1/3 of the lungs involved); 22% had grade 2 disease (1/3 - 2/3 involvement), and 47% had grade 3 (> 2/3 involvement).
Other pulmonary findings included prior lung transplant in 5% of patients, pleural effusion in 8%, pneumothorax in 6%, and dilatation of the thoracic duct (5%).
The abdominopelvic images showed that 42% of the patients had angiomyolipoma (AML). The masses can overtake the kidneys, and without a diagnosis of LAM, unnecessary nephrectomies have been performed in the past. Embolization is a more appropriate treatment, and can often save the kidney, Avila said.
"These benign [kidney] masses continue to grow until they start bleeding, and the patient ends up in the emergency room," Avila said.
In all, 64% of patients had a single renal AML, 29% had multiple renal AMLs, and 5% had undergone nephrectomy due to renal AMLs. Thirty-six percent of the renal AMLs were atypical in appearance, i.e., fat was not visualized on CT.
CT also revealed severe ascites in 9% of patients, retroperitoneal fatty masses in 6%, and fatty liver masses in 4%. In 24% of patients the abdominal lymph nodes contained low-attenuating material consistent with chyle.
"LAM cells can start narrowing the lumen of the lymphatic vessels. This happened in 23% of patients," he said. "In the pelvis it looks like ovarian cancer, with enormous masses. In the abdomen and pelvis, they get enlarged lymph nodes. You're thinking it's lymphoma, but stick a needle in it and it's LAM.... Behind the heart, [LAM can cause] premature contractions of the heart. Anywhere there are lymphatics you can have this."
LAM sufferers often report worsening symptoms as the day progresses -- a key to diagnosing the disease, Avila said. In a subgroup of 14 patients, CT showed that 13 had masses that grew anywhere from 4% to 564% between morning and afternoon. For follow-up CT, it's important to image patients at roughly the same time of day, Avila said.
The study concluded that CT is a useful diagnostic tool for distinguishing LAM from lymphomas and other solid lymphatic masses, and that CT also explains the worsening of symptoms as the day progresses. Moreover, the extent of disease visualized on CT correlated closely with patients' symptoms, the authors wrote.
The goal is to someday gather as many of the estimated 350 patients as possible, and begin some kind of drug trial. That day could be far off, however, because a suitable therapeutic agent hasn't been identified, Avila said.
"The treatment that has been used for years and years has been estrogen replacement with progesterone, and progesterone has done nothing. So it's more of an anecdotal type of treatment," he said.
By Eric BarnesAuntMinnie.com staff writer
May 23, 2001
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