Onchocercomas measure on average 0.5 to 2 cm in diameter and often can be visualized or palpated.14 These nodules can be misdiagnosed up to 5% of the time by physicians in endemic areas. Most commonly, they are confused with lymph nodes, lipomas, intradermal cysts, cancer, and foreign body granulomas. Our patient demonstrated an onchocercoma deep in his left buttock. Cutaneous incision and blunt dissection of an additional subcutaneous mass of the left axilla of our patient demonstrated a steatocystoma. Because some onchocercomas are deep in tissue around bones and in muscle and cannot be detected, nodulectomy of all palpable nodules does not always cure the patient. Nevertheless, nodulectomy should always be considered in patients who live outside endemic areas, as they have a low risk of reinfection, and might be cured if they do not have occult nodules.5 Ultrasound has been effective in discovering nonpalpable lesions but only when technicians are trained in distinguishing onchocercoma morphology.15
The treatment of choice for onchocerciasis is one dose of oral ivermectin 150 mg/kg every 6 months for up to 10 years.16-18 The drug works at the γ-aminobutyric acid receptors, impairing the neuromuscular function of the microfilariae, which leads to paralysis and death of most of the microfilariae 2 to 3 days after the first dose. The most common adverse effects of the medication are myalgia, rash, node tenderness and swelling, pruritus, fever, chills, and localized edema. These result from a hypersensitivity reaction to massive microfilariae death. Most side effects are usually mild to moderate and occur in 9% of patients.19 Patients are treated semiannually, which is the lifespan of microfilariae. This optimizes the therapeutic benefit of the drug.16
Unfortunately, ivermectin does not kill adult worms that can continue to reproduce for many years. This is why nodulectomy is performed as an adjunct therapy semiannually. It is also why treatment may need to continue for up to 10 years—the lifespan of the adult worm. In vitro research on potential macrofilaricidal compounds has given some promising leads.20
Because onchocerciasis has a devastating impact on millions of impoverished people worldwide, Merck & Co., Inc., established the Mectizan Donation Program in 1987, providing ivermectin treatments free of charge to all endemic areas. Since then, more than 250 million doses of ivermectin have been administered.21 There is still no adequate vaccine. Only through continuous surveillance and treatment can this preventable cause of blindness be reduced or eliminated. back to top