DOI 10.1378/chest.94.4.862 1988;94;862-865Chest

 M H Caceres and R M Genta Strongyloides stercoralis infection.Pulmonary microcalcifications associated with

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Pulmonary Microcalcifications Associated withStrongyloides stercoralis Infection*

�Fmm the Department of Pathology and Laboratory Medicine,Veterans Administration Medical Center and University of Cincin-nati College of Medicine, Cincinnati.

Reprint requests: Dr Genta, Pathology, 113, VA Hospital, Cincinnati45220

862 Pulmonary Microcalcifications Associated with S stercolans Infection (Caceres� Genta)

laboratorYandanimalstudies

M.H. Caceres, M.D.; and R.M. Genta, M.D.

Diffuse alveolar deposits of calcium phosphate have beenidentified in the lungs of two prednisolone-treated beagles

with chronic S stercoralis infection. Such lesions have not

previously been described in dogs and have not been foundin humans in association with either strongyloidiasis orprolonged steroid therapy. S stercoralis infections in the

S trongyloides stercoralis is an opportunistic para-

sitic nematode now recognized as an increasingly

important cause of morbidity and mortality in immu-

nocompromised 12

Adult worms reside within the mucosa of the small

intestine where they produce eggs that hatch, liber-

ating rhabditiform larvae. While most of these larvae

are passed with the stools into the external environ-

ment, some rapidly molt into infective filariform

larvae, which penetrate the colonic wall, enter venules

and lymphatics and reach the pulmonary circulation.

In the lungs, the larvae break out of the capillaries

into the alveolar spaces, then crawl upwards to the

larynx and are swallowed into the esophagus. Upon

reaching the duodenum, the parasites continue their

maturation and eventually establish within the mu-

cosa.3 Because of the unique ability to undergo this

autoinfectious cycle, S stercoralis may persist indefi-

nitely in its hosts, usually causing only mild intermit-

tent gastrointestinal symptoms.4 In immunocompro-

mised patients, the rate ofautoinfection is accelerated,

and ever-increasing numbers oflarvae migrate through

the lungs, where they may cause fatal hemorrhage,

infection, and respiratory failure.�9

To study the immune responses of immunocompe-

tent and immunosuppressed hosts against S stercora-

us, we use a canine model that closely reproduces the

parasitologic and pathologic events of human strongy-

loidiasis. 10-12

During the pathologic examination of two of these

experimentally infected animals, we discovered the

industrialized world are frequently found in patients onmaintenance regimens of corticosteroids. We suggest thatthe possibility that pulmonary calcifications represent anunsuspected complication in these patients should be inves-tigated.

presence of diffuse microcalcifications in their lungs.

This finding is of interest because such lesions have

not been described previously in either humans or

animals infected with S stercoralis, and may represent

an overlooked complication of prolonged strongyloi-

diasis in hosts treated with corticosteroids.

METHODS

Two specific parasite-free, four-month-old male beagles from

commercial sources were acquired to serve as donors of S stercoralislarvae. The animals originated from different litters and were notdirectly related. After one month of acclimatization, each dog was

inoculated with 2,000 S stercorahs filariform larvae obtained fromthe fecal cultures of other experimentally infected beagles. The

parasite strain, originally isolated from a Thai woman, has beenmaintained in our laboratory by repeated passage in dogs since

1983. Both animals developed patent infections within three weeksafter inoculation, and one month later were placed on a daily

regimen of prednisolone (4 mg/kg per os). Blood samples werecollected at monthly intervals from both animals throughout the

experimental period. Clinical monitoring was performed by an

animal health technician and a consulting veterinarian.

Dog 123 was maintained for 24 months. The course of theinfection was characterized by the passage of large numbers of S

stercorali.s larvae in the feces (between 1,000 and 9,500 larvae per

gram per day), and by long asymptomatic periods alternated by

bnefepisodes ofdiarrhea, anorexia, and occasional fever. At no time

was there clinical evidence of respiratory distress. Relevent labora-

tory findings were normal. Serum calcium levels were measured at

six time-points and varied between 1.97 and 2.99 mmol/L (normal

for beagles 2. 10-2.80 mmolJL); phosphorus levels were between

1.29 and 2.35 mmol/L (normal 0.81-2.31 mmolJL). These variations

are normal during the growing period of beagles,11 and were notdifferent from those of the other experimental animals in ourlaboratory. During the last month oflife, the dog lost approximately20 percent of its weight, developed bloody diarrhea, and became

completely anorexic. Euthanasia was followed by a complete nec-ropsy.

Dog 280 was maintained for 32 months. Except for the smaller

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CHEST I 94 I 4 I OCTOBER, 1988 863

FIGURE 1. Section of lower left lobe of dog 123. The irregularcalcified structures measure between 20 and 140 microns. Most areattached to septal walls, but some are loose in the alveolar spaces.No inflammatory response is present (H and E, original magnifi-

cation X 250).

number of larvae passed in the feces (rarely exceeding 3,000 per

gram per day), the course of the infection was similar to that of dog

123. No sign of respiratory disease was apparent during the entire

period of observation. Serum calcium levels were measured five

times and were between 1.99 and 2.85 mmol/L, and phosphorus

between 1.2 and 2.2 mmolIL. Euthanasia was performed when the

animal developed severe diarrhea, vomiting and rapid weight loss.

A complete necropsy was performed immediately after death.

Necropsy Results

The findings were similar in the two animals, and are reported

together. Grossly, there was generalized edema and hemorrhagic

areas throughout the small intestine, more severe in the duodenum

and proximal jejunum. The spleen was small and had a shrunkenappearance. Mesenteric lymph nodes were considerably enlarged.

The adrenal glands were markedly reduced in size. The lungs of

both dogs were normal in size, appearance, and consistency. Theywere inflated with 10 percent buffered formalin for fixation. No

abnormality was noted when fixed lungs were later cut to obtain

samples for histologic examination.

Microscopically, sections of the small intestine showed innum-

berable adult worms, eggs, and larvae within the duodenal andjejunal submucosa. Evidence of longstanding immunosuppression

was apparent in the spleen, where the white pulp was almost

completely devoid oflymphocytes, and in the adrenal glands, whichrevealed narrowing of both zona fasciculata and reticularis.

All sections of the lungs from both dogs showed an identical

appearance. Innumerable deposits of a material that, when stained

with hematoxylin-eosin (H and E) had the dark purple appearance

of calcification, were present within the alveolar septa, or loose in

the alveolar spaces (Fig 1). Their size varied between 20 and 140

microns, and their shape was generally irregular.

Special stains showed that the majority of these formations

consisted ofa central core ofvon Kossa-positive material surrounded

by a thin layer of an amorphous substance that reacted faintly withperiodic acid-Schiff(PAS).

When the structures were examined by x-ray microprobe (Kevex

7000, Kevex International Corp, Foster City, California) they showed

two K alpha bands at 3.68 and 2.01 Ke\� respectively, indicatingthat they consisted ofcalcium phosphate (Fig 2).

Light microscopic examination oflungs and other organs revealed

neither granulomas nor lesions suggestive of viral inclusions.

DIsCussIoN

The pulmonary pathology of immunosuppressed

patients who succumb to strongyloidiasis is likely

related to the large numbers of larvae reaching the

lungs during hypennfection. Massive intra-alveolar

hemorrhage, a common cause of death in these

patients, probably represents the cumulative effect of

the microhemorrhages produced by each larva in its

effort to exit from the capillaries into the air spaces.

When only a small number of parasites migrate

through the lungs at any given time, as happens during

the course of chronic uncomplicated infections, the

blood loss is minimal and remains clinically silent. In

contrast, the lesions caused by thousands of worms

may result in fatal hemorrhages. 1.2

Bronchopneumonia, another common complication

of disseminated strongyloidiasis, is probably the con-

sequence oftwo co-factors, the tissue damage inflicted

by the invading larvae, and the sepsis that frequently

follows the larval transmigration from the colon into

the bloodstream . 2,5,8

Calcified forms compatible with S stercoralis worms

FIGURE 2. Scanning electron photomicrograph of amedium-sized calcification(left)(original magnification,x 900). The K alpha bands at 3.68 and 2.01 KeV

demonstrated by x-ray microprobe analysis (right) in-

dicate that the structure consists ofcalcium phosphate.

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864 Pulmonary Microcalclficatlons Associated with Ssterco!ails Infection (Caceres� Genta)

were identified in the parathyroids, adrenals, pancreas,

kidneys, prostate and lymph nodes of one patient who

died of disseminated trogydis.’4 However, pul-

monary calcifications have not been described in any

ofthe more than 300 reported cases ofthis yn’4

Likewise, neither dogs nor primates used as models

of this parasitosis have been noted previously to

develop the unusual lesions observed in these two

15.16 In this respect, no other dog in our laboratory,

including siblings of the two study subjects, has ever

developed similar lesions. These include dogs infected

with S stercoralis and treated with prednisolone, dogs

infected but not immunosuppressed, and uninfected

dogs, both immunosuppressed and untreated. How-

ever, we had not previously maintained infected im-

munosuppressed animals for longer than eight months.

Prednisone alone is not a known cause of pulmonary

calcification, neither in humans nor in animals. In a

recent series of immunosuppressed dogs followed for

a year after a renal transplantation, none ofthe animals

was reported to have pulmonary cal’7 Other

causes of calcification, such as histoplasmosis or viral

infections, have a characteristic morphology which can

be readily distinguished from the lesions seen in our

dogs. In fact, we were unable to find in the veterinary

literature any case with lesions similar to those ob-

served in our dogs.

In humans, pulmonary microlithiasis is a rare dis-

ease of uncertain etiology. In the majority of the

approximately 160 cases reported in the literature, it

was an incidental finding in asymptomatic patients,’�

and the diagnosis was usually made on the basis of the

typical radiologic pattern. Although several hypothe-

ses have been put forward to explain its pathogenesis,

including the possibility of a congenital error of

metabolism at the level of the alveolar membranes,

and the secondary calcification ofan exudative process,

the etiology of this entity remains obscure.

The calcifications seen in our dogs, although diffuse

to all lobes of both lungs, showed differences from

those of the human cases. Most small lesions were

connected with the alveolar septa and were covered

by a noncalcified thin membrane. Many of the larger

structures, frequently of irregular shape, were lying

free in the alveolar spaces, as if they had detached

from their supporting stem. None of the lesions

contained structures that could be demonstrated to

represent calcified parasites.

The long-term administration of steroids increases

the renal excretion ofcalcium and may lead to second-

ary hyperparathyroidism,2’ which in turn may have

promoted the deposition of calcium phosphate on the

alveolar lesions caused by the continuous passage of

the larvae through the lungs.

In some series from endemic areas, older men with

chronic obstructive pulmonary disease have been

found to be infected with S stercoralis. Several of

them had been on maintenance doses of corticoste-

roids for years.� Although it must be made clear that

the findings in these two dogs may not necessarily

indicate that a similar association exists in humans, we

feel that a specffic search for diffuse pulmonary micro-

calcifications in such patients might reveal whether

this is another unsuspected complication of this sys-

temic parasitosis.

ACKNOWLEDGMENTS; We are grateful to Dr. C. Kurtis Kim forthe performance of the x-ray microprobe analysis. This work wassupported by the Medical Research Office of the Veterans Admin-istration, Washington, DC.

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DOI 10.1378/chest.94.4.862 1988;94; 862-865Chest

M H Caceres and R M Gentainfection.

Pulmonary microcalcifications associated with Strongyloides stercoralis

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