Lymphatic filariasis presenting as a soft tissue swelling in midarm: A histopathological diagnosis at unusual site.

Filariasis is a major social health problem in tropical countries like India. Wuchereria bancrofti accounts for 95% cases of lymphatic filariasis. The adult worm resides in the lymphatics and lymph nodes and causes little inflammatory response as long as it is alive, but granulomatous reaction is noted once the death of parasite occurs. In the present case, spectrum of inflammatory response is noted to the adult and larval form, which forms a soft tissue mass, masquerading as a soft tissue tumor clinically. Copyright:

INTRODUCTION

Filariasis is a chronic disabling parasitic disease and causes a major public health problem in tropical and subtropical countries such as India, China, Indonesia, and the Far East. It is caused mainly by nematode worms Wuchereria bancrofti, Brugia malayi, and Brugia timori, among which W. bancrofti is associated with almost 99.4% of cases and B. malayi with 0.6% cases of lymphatic filariasis in India.[1] Filariasis presenting as soft tissue swelling is very rare.[2345] Although there are cases describing the cytological aspect of this entity, only few cases describe the histopathology.[6] Herein, we report a rare case of filariasis presenting as subcutaneous soft tissue swelling which was diagnosed by histopathological examination as inflammatory granulomatous nodule formed due to adult and larval form of W. bancrofti.

CASE REPORT

An 18-year-old male residing eastern part of India came to the surgery outpatient department with a chief complaint of swelling over the right arm. On clinical examination, the swelling was of size 2 cm in maximum dimension, subcutaneous, mobile, and nontender. With a clinical diagnosis of lipoma, fine-needle aspiration cytology (FNAC) was suggested. The procedure was done twice and yielded a fluid-like scanty material. Smears were stained with Diff-Quik stain and hematoxylin and eosin stain. Microscopy revealed few lymphocytes, cyst macrophages, neutrophils, and histiocytes over a fluid-like background. With these findings, a diagnosis of benign cystic lesion with features of inflammation was suggested. Excision of the mass was done, and the gross received was two bits of nodular structures together measuring 2.5 cm × 2.0 cm, which was bisected and all embedded.

Microscopy revealed a circumscribed lesion surrounded by a fibrous capsule within which the stroma was myxoid and contained many dilated lymphatics [Figure 1a]. Many lymphatics showed fibrous obliteration of the lumen with proliferation of myofibroblasts within the lumen (inset). One focus revealed central necroinflammatory debris [Figure 1b] which on higher magnification showed a plenty of coiled microfilarial organisms of varying sizes at the periphery and few straight forms within the debris [Figure 1c and d]. Other bit of tissue was a lymph node and showed central granulomatous reaction comprising palisaded histiocytes and foreign-body type giant cells surrounding many adult gravid form of female filarial organism and dead forms [Figure 2a]. On higher magnification, they had outer refractile cuticular layer and few of which contained the embryonated eggs and coiled to straight larvae within the body cavity [Figure 2b and c]. Still, on higher magnification, microfilarial organism was slender, sheathed with multiple coarse discrete nuclei extending from head to tail, and the tip of the tail was free of nuclei which were consistent with W. bancrofti [Figure 2b]. The dead worms were fragmented and inflammatory cells were seen invading the body cavity [Figure 2d]. Surrounding soft tissue showed dense inflammation comprising plasma cells, eosinophils, neutrophils, and also mast cells. The routine hemogram showed hemoglobin: 14.2 gm%, total leukocyte count: 6850/cumm, with normal differential; absolute eosinophil count: 274/cmm; total platelet count: 220,000/cumm. Midnight peripheral smear was negative for microfilarial organism, but serum immunochromatography test for filarial antigen was positive. The patient was treated with diethylcarbamazine (150 mg) twice daily for 12 days with antihistaminic and single dose of albendazole + ivermectin.

Figure 1

(a) Many dilated lymphatics (arrow) with one focus depicting the necroinflammatory debris (asterisk), fibrous obliteration of the lumen by myofibroblastic proliferation (inset) (H and E × 40), (b) neutrophilic abscess (H and E, ×100), (c and d) Aggregates of curved form of microfilariae and some linear forms of microfilariae (H and E, ×400)

Figure 2

(a) Live and dead adult worms with palisading arrangement of histiocytes (arrow) and foreign body-type giant cell reaction (H and E, ×100). Live adult parasite with larval forms within the body cavity (b) longitudinal section and (c) cross-section (H and E, ×400), (d) dead worm (arrow) with inflammatory infiltrate within the body cavity and fragmentation (H and E, ×400)

DISCUSSION

Filarial adult worm resides in lymphatics and/or lymph nodes, while the larval form circulates in the peripheral smear which is taken by the mosquito and the disease is transmitted. Lymphedema due to lymphatic blockage and lymphadenitis are usual mode of presentation of filariasis; however, extralymphatic filariasis is rare and has been reported in uncommon sites, including skin and soft tissue swelling, breast, thyroid nodule, salivary gland, cervicovaginal smear, ovarian cyst, effusion fluids, and urine, bronchial, laryngeal, and pharyngeal brushings.[27] The larval form possibly reaches the tissue space due to lymphovascular obstruction causing extravasation.[8]

Viable adult forms have intact outer cuticular layer with body cavity containing intestine, testis, or ovary. Female gravid worm contains an embryo coiled larval form. The dead parasites have fragmented outer membrane, body parts, or calcification.[9] They usually evoke the inflammatory reaction, which causes tissue injury, foreign body-type giant cell reaction, and fibrosis. The presence of dead and viable form in the same site is also described in the literature signifying that inflammation is probably caused due to dead parasites.[9] However, morphological details of viable and dead forms are not clearly evident in histopathology due to fixation artifact.[910]

Peculiarity in our observation is that both larval forms and adult forms were seen in separate tissue with different immune response. The microfilarial form evokes a neutrophil response with the formation of microabscess, while adult form showed basically inflammation comprising histiocytes, multinucleated giant cells, lymphocytes, plasma cells, eosinophils, neutrophils, and good number of mast cells. The presence of eosinophils surrounding the pathological site highlights the presence of dead parasite, which was also noted in the present case.[8]

The disease presentation ranges from subclinical to acute and chronic manifestations such as lymphangitis, lymphadenitis, elephantiasis of genitals, legs, and arms or hypersensitive states such as pulmonary eosinophilia or sometimes filarial arthritis.[1] W. bancrofti and Brugia species cause lymphatic filariasis and presentation as subcutaneous nodule is very rare. The skin and subcutaneous filariasis are mainly caused by Onchocerca volvulus and Loa loa.[4]

Filariasis is usually diagnosed by the demonstration of microfilaria in stained or unstained blood films and detection of filarial antigen in the low level of microfilaremia. However, in endemic areas, a majority of the affected individuals remain asymptomatic with continued disease transmission.[7] Our case retrograde midnight sample did not reveal any microfilarial organism or eosinophilia.

FNAC is a well-known diagnostic procedure for the evaluation of subcutaneous soft tissue lesions. Different parasites such as filariasis, hydatid disease, and cysticercosis presenting as soft tissue lesion have been described in the literature.[11] Microfilaria is sometimes diagnosed in FNAC smears, but detection of adult form is very unusual.[5] But in our case, no filarial organisms were detected in the cytology slides. Although histopathology is not needed in all cases, it confirms the diagnosis when FNAC does not yield the organism.

CONCLUSION

Filariasis is not uncommon in tropical countries like India, but presenting with a soft tissue nodule with heavy load of parasites, especially in histopathology sections, is extremely uncommon incident. This unique case will impart some awareness of diagnosing and subjecting proper therapy.

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Conflicts of interest

There are no conflicts of interest.