Physical Examination
Localized inflammatory responses to dead or dying microfilariae are almost entirely responsible for the clinical manifestations of the disease. In a severely infected person, 100,000 or more microfilariae die each day. The earliest symptoms are fever, arthralgia, and transient urticaria involving the trunk and face. Onchocercomas, the most characteristic skin lesions, are often present.
The most common dermatologic manifestation of onchocerciasis is diffuse papular dermatitis. This symptom is accompanied by intense pruritus, which is the earliest sign of the disease in some patients. [1]
The following is a summary of the clinical classification system for onchocercal dermatitis, which Murdoch et al developed to standardize and facilitate the collection of data worldwide [25] Ref26}:
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Acute papular onchodermatitis (APOD) is characterized by a solid, scattered, pruritic papular rash. The diameter of the papules is at least 1 mm. Vesicles or pustules at the apex may or may not be present. The obliteration of the skin creases due to edema also may or may not be present.
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Chronic papular onchodermatitis (CPOD) involves a scattered, pruritic, hyperpigmented, and flat-topped papulomacular rash. The diameter of the papules is at least 3 mm, with or without excoriations.
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Lichenified onchodermatitis (LOD) is characterized by raised, discrete, pruritic, and hyperpigmented papulonodular plaques associated with lymphadenopathy. The lesions may be confluent, with or without the presence of excoriations. APOD or CPOD may also be present.
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Atrophy (ATR) involves wrinkled and dry skin. Firmly pressing the edge of a finger along the skin reveals additional fine wrinkles. In patients younger than 50 years, ATR is scored as a significant abnormality.
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Depigmentation is characterized by areas of incomplete pigment loss, with associated islands or spots of normal pigment surrounding hair follicles. Leopard skin is similar, except that it is characterized by a complete loss of pigment, with islands or spots of normally pigmented skin around the follicles.
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Palpable onchocercal nodule, as shown below, is a term used to describe onchocercomas that are palpable at bony prominences.
Onchocercoma. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Lymphadenopathy is characterized by lymph nodes 1 cm or larger in diameter. They may or may not be tender.
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Hanging groin (HG) involves the folds of inelastic, atrophic skin in the inguinal areas. The condition may be unilateral or bilateral, and it may involve enlarged lymph nodes. See the images below.
Hanging groin sign. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Hanging groin sign. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Lymphedema (LYM) is characterized by edema of a limb or external genitalia.
Onchocercomas are fibrous, subcutaneous nodules containing adult worms. These nodules are generally located over bony prominences, and they are easily palpable. Deep nodules, commonly located around the pelvis, can be more difficult to detect. The number of palpable nodules is not correlated with the microfilarial load or the severity of disease. Identifying every nodule is important for proper management. In Africa, the nodules are often observed along the iliac crests, ribs, greater trochanters, and ischial tuberosities. Juxta-articular areas, such as the knees (as shown below), elbows, patella, and scalp, may also have nodules.
Onchocercoma. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
In the American forms, nodules are fewer and have a greater tendency to be located on the scalp. [26] In patients with scalp nodules, the risk of ocular complications is generally higher than that of patients without scalp nodules. Onchocercomas are less common in the Yemen form of the disease than in other forms.
Onchocercal dermatitis, as shown below, is the most common symptom of the disease. [1] Its initial manifestations, which can occur anywhere on the body, include itching, scratching, and alterations in skin pigmentation. Pruritus may be intermittent and mild, continuous and severe, or absent. A maculopapular rash may appear anywhere on the body at any time. The papules may be small and densely packed or large and separated. The maculopapular rash is often associated with severe pruritus. Excess scratching may lead to bleeding, ulceration, and secondary infection (a condition West Africans call craw-craw).
Dermatitis associated with microfilaria. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Sowda, a severe form of dermatitis first described in Yemen, is associated with an active delayed hypersensitivity response. Many patients are travelers or temporary workers in nonendemic areas. These patients have dark, thickened, intensely pruritic skin with papules. The regional lymph nodes are soft, nontender, and enlarged. Sowda is usually localized to a single lower extremity. A less common, more generalized form can involve both lower extremities or other parts of the body. Patients have either focal swelling or a more diffuse LYM. Skin-snips do not usually contain microfilariae. Sowda may also be found in patients in West Africa, Ethiopia, Sudan, [27] Cameroon, Venezuela, and Ecuador.
Leopard skin is a characteristic finding in older patients. Leopard skin involves depigmentation of the pretibial areas of the lower extremities. This pattern is initially seen as discrete depigmented macules, with sparing of the hair follicles. Later, the macules may become confluent, involving a large area of the anterior portion below the knee, as shown below. This pattern can sometimes be seen in the groin or lower abdomen as well.
Leopard-spot pattern of depigmentation on the shins. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
HG or adenolymphocele is a severe degenerative condition in older individuals. The inguinal and femoral lymph nodes become progressively enlarged and fibrotic, leading to lymphatic obstruction. Concomitantly, progressive destruction of elastic fibers leaves the skin thinned and wrinkled. The atrophied skin tends to hang in apronlike folds under the weight of the accumulating lymphedematous tissue. This condition is more common in men than in women.
Ocular manifestations of onchocerciasis are late, serious reactions that occur in about 5% of affected persons. Infection of the cornea produces punctate keratitis in the areas around dead microfilariae. This condition eventually clears when the inflammation settles. Severe and prolonged infection over a number of years is likely to produce sclerosing keratitis, iridocyclitis, and uveitis. Permanent visual impairment, secondary glaucoma, or blindness is often the result. Posterior segment changes may coexist with anterior segment lesions. The changes are caused by inflammation around microfilariae that invade the retina via the posterior ciliary vessels. Choroidoretinal lesions are common around the optic disk or on the outer portion of the macula. Active optic neuritis is a major cause of blindness in many areas with endemic disease.
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Leopard-spot pattern of depigmentation on the shins. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Dermatitis associated with microfilaria. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Hanging groin sign. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Hanging groin sign. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Onchocercoma. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Onchocercoma. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Photomicrograph of a skin biopsy specimen from a patient with onchocerciasis. A worm is shown in cross-section. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
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Photomicrograph from a gravid female worm (hematoxylin and eosin]). Courtesy of Brooke Army Medical Center. All images are in the public domain.
