INTRODUCTION:Dirofilaria immitis has become increasingly recognized as an inadvertent human pathogen. Nodules related to dirofilariasis are commonly misdiagnosed as malignant tumors. The lesions most often present as a single pulmonary nodule, but occasionally multiple lesions are seen. The misdiagnosis can lead to patient morbidity and medico-legal risk.
CASE PRESENTATION:A 53-year-old male presented for a pre-liver transplant evaluation. He had complaints of dyspnea on exertion, paroxysmal nocturnal dyspnea, orthopnea, and occasional episodes of hemoptysis. His past medical history included cirrhosis, transjugular intrahepatic shunt, umbilical and inguinal hernias, and a remote positive tuberculin test. His social history was positive for heavy alcohol and drug use, and 60 pack-years of smoking. He denied any drug use for 20 years and quit alcohol in May 2005. He had lived in Kentucky and worked on a boat in the Gulf Coast area for the last 20 years. He denied having pets or foreign travel. His medications included Spironolactone, Lactulose, Milk Thistle, Hydrochlorothiazide, and Quinine. His vital signs were normal. He had poor oral hygiene, scattered petechia, and intermittent wheezing. Hepatomegaly, an umbilical hernia and bilateral inguinal hernias were noted on abdominal exam. Digital clubbing and pitting edema were present. No subcutaneous nodules were felt. The remainder of his physical examination was normal. His chest x-ray showed multiple bilateral nodular opacities. Computerized tomography confirmed four pulmonary parenchymal masses up to 2-3 cm, centrilobular emphysema, liver cirrhosis and multiple scattered subcutaneous nodules. Laboratory results including HIV, Secrum cryptococcal antigen and anti-neutrophil cytoplasmic antibody testing were all within normal limits or negative with the exception of an ALT 65, AST 135, platelets 151, INR 1.5, MCV 101.5. Because of the likelihood for malignancy or infection, he was referred to surgery and underwent thoracotomy and wedge resection. The patient developed massive post-operative hemoptysis at 24 hours requiring placement of a bronchial blocker. He subsequently required eleven days of mechanical ventilation and sixteen total hospital days. The wedge biopsy results demonstrated nodular necrosis with a central parasitic thrombosis containing fragments of Dirofilaria immitis. There was no evidence of fungi, AFB, or malignancy.
DISCUSSIONS:Human Pulmonary Dirofilariasis (HPD) is due to immature Dirofilaria worms accidentally infecting humans and causing pulmonary lesions. It is normally discovered in asymptomatic patients as a solitary nodule, but can present as multiple masses. Dirofilaria is seen in tropical, subtropical, and temperate environments, and is most commonly found in the states adjacent to the Gulf of Mexico and the southern Atlantic. Domestic dogs are the usual definitive host, but has been discovered in cats and other feral species. Mosquitoes are the most common vector, but flea, lice and ticks also can transmit disease. The differential diagnosis includes primary and metastatic tumors, lymphoma, sarcoid, Wegeners’ granulomatosis, eosinophilic granuloma, mycobacterial, fungal infections including histoplasma, cryptococcus and blastomycetes. Parasitic infections including echinococcosis, filariasis, and strongyloidosis are also possibilities. Morbidity due to Dirofilaria is due to the common radiological misdiagnosis of a primary or metastatic lung tumor, which usually leads to open lung biopsy or a wedge resection of the lung. There are no known fatalities due to HPD. The physical examination is usually noncontributory. Peripheral eosinophilia can be seen. Serology is not sufficient to make a diagnosis given the low sensitivity and specificity. Tissue confirmation is needed to make the diagnosis. Treatment is not needed for HPD.
CONCLUSION:Human pulmonary dirofilariasis should be considered in the differential diagnosis of single or multiple pulmonary nodules in patients from endemic areas. The misdiagnosis of HPD can lead to patient morbidity and medico-legal risk.
DISCLOSURE:Mark Vollenweider, No Financial Disclosure Information; No Product/Research Disclosure Information