Cases of human dirofilariasis have been reported in several countries around the world, including a large number in the Atlantic and Gulf Coast regions of the United States. Most commonly, these cases have subcutaneous or pulmonary involvement; however, there have been few reports of dirofilariasis involving structures such as large vessels, mesentery, the spermatic cord, and liver. We present a case of an unusual presentation of human dirofilariasis presenting as a shoulder abscess and what is presumed to be pulmonary and splenic involvement in a 55-year-old female.
Biology-life cycle of
A 55-year-old female initially sought medical attention for abdominal pain following a hernia repair. On presentation, her physical exam and routine bloodwork (including a complete blood count and chemistry profile) were entirely normal. She subsequently underwent additional diagnostic testing. The abdominal computerized tomography (CT) scan demonstrated multiple splenic hypodensities along with a left lower lobe nodule (see Figure
Abdominal imaging, revealing multiple splenic hypodensities.
Chest CT scan, revealing bilateral nodules.
After the acute episode of her abdominal pain resolved, the patient underwent additional evaluation. Her laboratory data showed that the liver function tests were within normal limits. Serum protein electrophoresis was within normal limits. Serologic testing including
Bone marrow aspiration and biopsy showed normal cellular bone marrow with maturing trilineage hematopoiesis. There was no evidence of any granulomatous or lymphoproliferative processes.
A transthoracic echocardiogram showed normal left and right ventricular size and function. There were also findings of minimal tricuspid valve regurgitation and mitral valve thickening. A repeated transthoracic echocardiogram with bubble study did not reveal a patent foramen ovale (PFO) or atrial septal defect. Although not conclusively proven by a splenic biopsy, the cardiologist consultant’s impression was that there was no cardiac cause for the presence of
Following this extensive evaluation, the patient was deemed to be clinically and radiologically stable. A repeated chest CT scan was ordered 1 year later in order to ensure stability. The CT scan confirmed the stability of the pulmonary nodules with no changes to heart size and no evidence of mediastinal or hilar lymphadenopathy.
The interesting aspect of this patient’s presentation is the presence of the splenic hypodensities and multiple pulmonary nodules. Published reviews have shown that 75–95% of pulmonary dirofilariasis presents as a single granuloma, which was not the case in this patient [
The first explanation under consideration is a cardiac defect, which is why an echocardiogram was pursued. The thought process was that if the patient had PFO or a septal defect, there would be a venue through which an adult worm in the right ventricle could be embolized and enter both the pulmonary circulation and the systemic circulation to end up in the spleen. As reported, the patient had no evidence of such defect on color Doppler or on bubble study, making this explanation less likely. A second explanation could be that there was dissemination of the worm during surgical excision of the patient’s right shoulder mass.
Although in this case neither the splenic nor pulmonary lesions were biopsied, the stability of the lesions in conjunction with the patient’s history of subcutaneous dirofilariasis makes dirofilariasis the most likely explanation. These lesions have been described in the literature to be well circumscribed and yellowish-grey in color, with normal lung parenchyma surrounding the lesion when biopsied. Microscopic pathology has been reported to show a central zone of necrosis, with a granulomatous zone with epithelial cells, plasma cells, lymphocytes, and a few scattered giant cells and an outer layer of fibrous tissue. Additionally, fragmented, necrotic portions of the embolized worm have been reported (see Figure
Courtesy of trends in parasitology: a coin lesion excised from a human lung showing a well-demarcated granuloma. Cross sections of the worm are highlighted by the black arrows [
The most common symptom reported has been cough, with a lesser incidence of chest pain, fever, and hemoptysis. [
From a diagnostic perspective, video-assisted thoracoscopic biopsy is the most direct technique for diagnosing human pulmonary dirofilariasis as less invasive serologic testing is not currently available [
Risk factors for dirofilariasis in humans are dependent on the size of the dog population, the prevalence of canine dirofilariasis in the population (see Figure
Courtesy of veterinary parasitology: US distribution of dogs testing positive for
As the patient was asymptomatic at follow-up, surgical intervention for these stable pulmonary and splenic lesions was deemed to be unnecessary (unlike the subcutaneous lesion in her right shoulder which required surgical resection for both diagnostic purposes and resolution of her pain).
A literature search for cases of human splenic dirofilariasis yielded no results to date. Although not conclusively proven, the splenic hypodensities can be assumed to be related to the presence of
Adarsha Selvachandran and Dr. Foley vouch for scientific integrity of the study and explicitly confirm that the paper meets the highest ethical standards for authorship.
The authors have stated that they have no competing interests.
Dr. Foley is the sole contributor to this paper.