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Filariasis: Differential Diagnoses & Workup
Updated: Nov 23, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
| Angioedema | Milroy Disease |
| Asthma | Scrotal Trauma |
| Hodgkin Disease | Testicular Trauma |
| Hydrocele | Testicular Tumors: Nonseminomatous |
| Leprosy | |
| Lymphedema | |
| Lymphoma, Non-Hodgkin |
Other Problems to Be Considered
Lymphatic filariasis
Bacterial or fungal lymphadenitis (eg, sporotrichosis resulting from Sporothrix schenckii infection)
Recurrent streptococcal lymphadenitis (ie, relapsing erysipelas)
Congenital or hereditary lymphedema (eg, Milroy syndrome)
Nonfilarial elephantiasis (highlands of East Africa)
Congenital hydrocele
Epididymal cysts
Carcinoma of testis and/or scrotum
Lymphosarcoma
Occult filariasis
Asthma
Bacterial monoarthritis
Bacterial breast abscess
Idiopathic or poststreptococcal glomerulonephritis
Onchocerciasis
Vitiligo
Trachoma
Lepromatous leprosy
Loiasis
Hereditary and/or localized idiopathic angioedema
Workup
Laboratory Studies
- Detection of microfilariae: The traditional diagnostic method is to demonstrate microfilariae in the peripheral blood or skin.
- Detection of microfilariae in blood
- The microfilariae of all species that cause lymphatic filariasis and the microfilariae of L loa, M ozzardi, and M perstans are detected in blood.
Filariasis. Microfilariae of Mansonella perstans in peripheral blood.
- Capillary finger-prick or venous blood is used for thick blood films. Venous blood also can be concentrated or passed through a Nuclepore filter before being examined microscopically. The species of infection then can be determined by the microscopic appearance. W bancrofti and Brugia species have an acellular sheath. W bancrofti has no nuclei in its tail, whereas B malayi has terminal and subterminal nuclei.
Filariasis. Appearance of microfilariae after concentration of venous blood with a Nuclepore filter.
- Microfilaria may periodically appear in the peripheral circulation, and the blood should be examined at different intervals over a 24-hour period to achieve the best chances of detection. Bancroftian and brugian filariasis tend to show nocturnal periodicity, so it is recommended that samples be collected between 10:00 pm and 2:00 am.
- Provocation of nocturnally periodic microfilariae may be achieved with a daytime dose of DEC at 1-2 mg/kg.
- Microfilariae may also be observed in chylous urine and hydrocele fluid.
- Microfilariae may be absent in patients with ADL or late chronic lymphatic disease.
- Microfilariae are typically absent in patients with loiasis, unless the infection has been present for many years.
Filariasis. Microfilaria of Wuchereria bancrofti in a peripheral blood smear.
- The microfilariae of all species that cause lymphatic filariasis and the microfilariae of L loa, M ozzardi, and M perstans are detected in blood.
- Detection of microfilariae in skin
- O volvulus and M streptocerca infections are diagnosed when microfilariae are detected in multiple skin snip specimens from different body sites from both sides of the body.
- In suspected cases of African onchocerciasis, the recommended sites for skin snips are the gluteus and calf. For American onchocerciasis, the scapula and deltoid skin are preferred.
- Detection of microfilariae in the eye: Microfilariae of O volvulus may be detected in the cornea or anterior chamber of the eye using slit-lamp examination.
- Detection of filarial antigen: The presence of circulating filarial antigen in the peripheral blood, with or without microfilariae, is now considered diagnostic of patent filarial infection and is also used to monitor the effectiveness of therapy. Commercial kits are available to test venous blood and can be quantitative (enzyme-linked immunoassay [ELISA]) Og4C3 monoclonal antibody–based assay) or qualitative (immunochromatographic). The former is one of the best predictors of worm burden13 ; the latter, although not as sensitive,14 was once considered the test of choice in field surveys. However, results from this test remain positive for 3 years posttreatment; hence, this test has been shown to be ineffective for the same reason.15
- Detection of filarial antibodies: The use of recombinant antigens for the diagnosis of onchocerciasis IgG4 antibodies has improved the sensitivity and specificity of serological assays. They are a marker of active infection.16 The usual IgG and IgE lack specificity (species differentiation) and usually crossreact with antigens of Strongyloides. In addition, they do not differentiate between past and recent infections. Thus, diagnosis based on recombinant antigens is useful only in expatriates but not in those living in endemic regions.
- Urine examination and microscopy: If lymphatic filariasis is suspected, urine should be examined macroscopically for chyluria and then concentrated to examine for microfilariae.
- Complete blood cell count: Eosinophilia is marked in all forms of patent filarial infection.
Imaging Studies
- Chest radiography: Diffuse pulmonary infiltrates are visible in patients with TPE.
- Ultrasonography
- Lymphatic obstruction of the inguinal and scrotal lymphatics can be demonstrated and monitored with ultrasonography. Ultrasonography has also been used to demonstrate viable worms, which are seen to be in continuous motion (ie, "filarial dance" sign). This imaging characteristic has been used to monitor the effectiveness of treatment.17
- Deep onchocercomas and vitreous changes in the eye can sometimes be detected with ultrasonography.
Other Tests
- The Mazzotti test allows a presumptive diagnosis of cutaneous filariasis when skin snip is negative for microfilariae. An intense pruritus is elicited within hours after a single small dose of DEC (50-100 mg). Steroids may be necessary to control this inflammatory reaction. The test must be used with caution in individuals who may be heavily infected because a severe systemic reaction can be provoked. A DEC patch test that causes a localized skin reaction may be used in such patients.
Procedures
- Lymph node or skin nodule biopsy: Obtaining these biopsy specimens is recommended only in patients with cutaneous filariasis, as excising nodes may further impede lymphatic drainage in patients with lymphatic filariasis. Adult worms of O volvulus and L loa are found in the nodules and fibrotic tissue of the skin. L loa worms occasionally can be dissected from the conjunctiva of the eye or bridge of the nose as they migrate through the subcutaneous tissues.
Filariasis. Adult worms of Wuchereria bancrofti in cross section isolated from a testicular lump.
Filariasis. Microfilariae of Loa loa detected in skin snips.
Histologic Findings
Lymphatic filariasis
Affected lymph nodes demonstrate fibrosis and lymphatic obstruction with the creation of collateral channels. The skin of individuals with elephantiasis is characterized by hyperkeratosis, acanthosis, lymph and fatty tissue, loss of elastin fibers, and fibrosis.
Onchocerciasis
Two areas are evident in onchocercomas: a central stromal and granulomatous inflammatory region where the adult worms are found and a peripheral fibrous section. Microfilariae in the skin incite a low-grade inflammatory reaction with loss of elasticity and fibrotic scarring.
Filariasis. Adult Onchocerca volvulus contained within onchocercomas of the skin.
More on Filariasis |
| Overview: Filariasis |
 Differential Diagnoses & Workup: Filariasis |
| Treatment & Medication: Filariasis |
| Follow-up: Filariasis |
| Multimedia: Filariasis |
| References |
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References
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Further Reading
Keywords
filariasis, bancroftian filariasis, elephantiasis, hanging groins, leopard skin, river blindness, sowda, loaiasis, loiasis, tropical pulmonary eosinophilia, TPE, adenolymphangitis, ADL
