A fifty-seven-year-old woman presented to the orthopaedic oncology service for evaluation of a painless mass in the left forearm, which had been slowly enlarging over several years. The patient's rheumatoid arthritis had caused finger deformities and diffuse rheumatoid nodules. At the time of presentation, the rheumatoid arthritis was being treated with abatacept, a T-cell costimulation modulator, but in the past it had been treated with other disease-modifying antirheumatic drugs. Additionally, she had a twenty-year history of anterior interosseous nerve syndrome of the right forearm, and a one-year history of anterior interosseous nerve syndrome of the left forearm, although the cause of these bilateral syndromes was unknown.
Physical examination demonstrated a firm, fixed, painless mass on the volar side of the left forearm, proximal to the wrist crease. The patient had an absence of flexor pollicus longus and flexor digitorium profundus function to the index and long fingers, consistent with the known anterior interosseous nerve syndrome. The remaining motor, sensory, and vascular examinations were unremarkable.
Radiographs revealed no osseous abnormalities. Magnetic resonance imaging revealed a single lobulated, well-circumscribed mass measuring 7.4 cm × 2.4 cm × 2.3 cm. With contrast imaging, the mass had a homogeneous signal with rim enhancement (Fig. 1). Adjacent soft-tissue edema and tenosynovitis involving the flexor digitorum superficialis and profundus tendon sheaths were noted. Given the inconclusive imaging findings and slow growth of the mass, a biopsy was recommended to establish a diagnosis. Routine laboratory work (complete blood-cell count and basic metabolic profile) revealed no abnormalities; erythrocyte sedimentation rate and C-reactive protein levels were not measured.
A yellow-tan mass firmly adherent to the surrounding inflamed tendons was found at the time of open excisional biopsy. The flexor digitorum profundus and flexor digitorum superficialis tendons were primarily involved. There was partial involvement of all other flexor tendons of the hand, with the exception of the flexor carpi ulnaris. The preliminary pathologic interpretation of a frozen section revealed only inflammatory tissue; therefore, the mass was removed, and debridement of the surrounding inflammatory tissue was performed. Permanent histological sections demonstrated necrotic tissue with surrounding inflammatory cells and visible parasites (Fig. 2). The parasite was identified as Trichinella spiralis with an antibody test.
Detailed questioning revealed a history of regular consumption of pan-seared foods, including wild game. There was uncertainty about the duration of the patient's infection because she could not provide the caregivers with a specific time when she had experienced any symptoms of trichinellosis (e.g., stomach discomfort, myalgia, weakness, fever, rash, and facial edema). Given that the patient reported that the mass had been present for years, it was believed that she had a long-standing infection. She was treated with a fourteen-day course of albendazole therapy as well as a tapering course of prednisone therapy to address the infection and the associated inflammation, respectively. At the one-year follow-up postsurgery, the patient had no symptoms, and there was no clinical evidence of recurrence.
Richard Owens is credited with naming and describing trichinellosis, but it actually was his medical student, James Paget, who made the discovery6,7. The infection was very common in the United States in the 1930s. During that time, it was estimated that one of every six persons had been infected with Trichinella spiralis at some point in his or her lifetime5. Currently, only about twelve cases per year are reported in the United States, probably as a result of federal legislative and public health measures regarding techniques to improve the safety of food preparation2,4-6. The leading cause of trichinella infections is the consumption of undercooked or raw pork or wild game (e.g., bear, deer, and cougar)5,8-10.
Eight species and three genotypes of Trichinella have been identified8,11,12. Trichinella spiralis is the most common species known to cause the infection in humans8,11,12. Trichinellosis caused by Trichinella spiralis generally consists of two phases: an enteral (intestinal) phase and a parenteral (muscular) phase1,9,10. The enteral phase begins with the ingestion of contaminated meat and continues as the ingested larvae are freed from their enclosed cysts by gastric fluids. Once the larvae reach the small intestine, they invade the columnar epithelium, mature into adult (female and male) worms, and begin mating within thirty to forty hours postingestion1,5,9. Five days after mating, newborn larvae are shed, and they cross into lymphatic channels and blood vessels, initiating the parenteral phase1,5,9,12. The enteral phase can be completely asymptomatic or present with nausea, diarrhea, abdominal cramping, and other gastrointestinal symptoms1,5,12. During the parenteral phase, the newborn larvae migrate to striated muscle cells or other organ systems within twenty days of development1,5,9,11,12. Once the larvae are in the muscle cells, symptoms such as diffuse myalgia, fever, headache, weakness, dysphagia, and facial edema may occur1,5,11,12. Additionally, larvae in the muscle can become calcified, which may lead to larvae death or persistence in a dormant state1,9-11. A calcified cyst can occasionally be seen on radiographs5,13. Clinical manifestations of trichinellosis in patients with long-standing infections have been confused with polyarteritis nodosa, dermatomyositis, and polymyositis14,15,16. Clinical symptoms during its biphasic clinical course are directly related to the amount of parasites ingested1,17, host immune response6, and the type of Trichinella species that is present12. Trichinellosis rarely results in death, but fatal infections are possible if the organism reaches vital organs1,5,9. To our knowledge, no cases of trichinellosis presenting as a soft-tissue mass have been previously reported in the orthopaedic literature.
A trichinellosis diagnosis is made based on clinical symptoms and history, with confirmation by serologic tests and/or muscle biopsy. Antibody tests are accurate in detecting circulating antibodies, but these tests frequently are not available in standard laboratories11. With a biopsy, the presence of live larvae in muscle can also confirm the diagnosis9. Additionally, histological evaluation can assist in determining if the infection is acute or chronic since a thickened capsule and coiled parasite is suggestive of an older infection11.
The most efficient way to prevent trichinellosis is to educate at-risk populations about the correct preparation of high-risk foods. One method of decontaminating infected pork is to freeze slices of meat that are more than 15 cm thick to −15°C (5°F) for at least three weeks, and slices of meat that are more than 50 cm thick for at least four weeks1,4,18. Freezing wild game is less effective because this type of meat frequently contains freeze-resistant strains1,18. In addition, curing, drying, microwaving, and smoking are equally inconsistent decontamination methods1,6. Cooking pork or wild game to a core temperature of 77°C (171°F) is lethal to the parasite and is considered the best way to prepare these foods prior to consumption1,6,9.
Medical management of trichinellosis is based on the stage of presentation and symptoms. The use of anthelmintics (e.g., albendazole and mebendazole) is effective in its treatment; however, the duration of treatment depends on the suspected duration of the infection1,5,6,9. In addition to the use of anthelmintics, anti-inflammatory agents may be used to treat the inflammatory reaction associated with the infection and, in severe cases, may be a vital part of the treatment regimen1,5,7. The decision to use prednisone in our patient was an attempt to limit any additional damage to the flexor tendons caused by the infection. Prednisone is often used in combination with other antirheumatic medications. Surgical management is not part of routine treatment for trichinellosis, but, in our case, surgery was necessary because of the atypical presentation (the soft-tissue mass). Surgery aided us in the diagnosis and allowed for debulking of the infection. The rate of recurrence with surgical treatment alone is not known; medical management following surgery, as used in our patient, is highly successful.
Several fungal and atypical bacterial infections are known to masquerade as soft-tissue tumors, but our case involved a rare parasitic infection presenting atypically as a pseudotumor. The most noteworthy risk factor our patient had for acquiring this infection was that she frequently consumed inadequately prepared wild game on a routine basis. It is unclear to what degree, if any, the patient's rheumatoid arthritis or its medical management contributed to the acquisition of this infection.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.