An 18-year old male cross-country runner presents with a swollen right knee. He says the swelling has been intermittent for the past month and has affected both knees. The patient has been treating the swelling with ice and ibuprofen. The patient is currently “between seasons” as he runs cross-country in the fall and track in the spring. He does not recall any related injuries from his competitive running.

His past medical history is positive for tympanostomy tubes that were placed when the patient was three for recurrent otitis media, recurrent strep infections (although the patient has not had any in the past two years), and a tibial stress fracture one year ago. He reports having a bad bout of the “flu” with fever, chills, malaise and myalgia about four months ago in the summertime. His current medications include Claritin for allergies and ibuprofen as needed. The patient is allergic to penicillin.

The physical examination reveals he is well developed and well nourished, and has no signs of acute distress. He weighs 150 lbs. and is approximately 5’11” without shoes. Vital signs include a heart rate of 60 beats per minute with a regular rhythm, a sitting blood pressure of 106/68, respirations of 16 per minute and a temperature of 98.6⁰F. In addition to normal findings with the heart and lungs, the patient has no abnormalities with the abdomen, skin or eyes.

Examination of the right knee reveals warmth, a large joint effusion with no erythema and a negative McMurray’s test. There is decreased range of motion, especially of flexion, and no ligamentous laxity. The patient has dorsalis pedis pulses of 2+ bilaterally and has symmetrical ankle jerk reflexes. There is no peripheral adenopathy. Examination of the left knee is unremarkable.

Anteroposterior (AP), lateral and oblique radiographs of the right knee reveal soft tissue swelling and a moderate joint effusion. The synovial fluid is cloudy with a white blood cell (WBC) count of 25,000, total protein of 4 g/dl and glucose of 70. The gram stain reveals no bacteria. The Lyme titer, erythrocyte sedimentation rate (ESR), rheumatoid factor (RF) and synovial fluid culture are pending.

Which of the following conditions is the most likely diagnosis?
A. Reactive arthritis (Reiter’s syndrome)
B. Juvenile chronic arthritis (juvenile rheumatoid arthritis)
C. Lyme disease
D. Osgood–Schlatter disease

Considering Possible Options In The Differential Diagnosis
A. Reactive arthritis (Reiter’s syndrome) is not the correct answer. Reactive arthritis occurs most commonly in young men. Most cases occur days to weeks after dysentery (Campylobacter, shigella, salmonella or yersinia) or a sexually transmitted infection (Chlamydia most commonly). This disease is characterized by a tetrad of arthritis, conjunctivitis, urethritis and mucocutaneous lesions.

The arthritis most commonly involves large joints, especially of the knee and ankle, and is asymmetric. One may see sacroiliitis and ankylosing spondylitis in up to 20 percent of patients with reactive arthritis.

At the onset of this disease, one will often note systemic symptoms such as fever, weight loss and malaise. Mucocutaneous lesions may involve the gastrointestinal (GI) or genitourinary (GU) tract and include urethritis, stomatitis, keratitis and keratoderma blennorhagicum. Radiographic abnormalities of affected joints would include soft tissue swelling, juxtaarticular osteopenia and joint space narrowing.

Nonsteroidal antiinflammatory drugs (NSAIDs) are the mainstay of treatment. In patients with Chlamydia infection, tetracycline shortens the duration of symptoms. Clinicians sometimes use sulfasalazine for patients who do not respond to NSAIDS or tetracycline.

B. Juvenile chronic arthritis (juvenile rheumatoid arthritis) is not the correct answer. Juvenile chronic arthritis is generally divided into three subgroups: pauci- or oligoarticular, systemic or acutely febrile, and polyarticular juvenile arthritis.

With pauci- or oligoarticular juvenile arthritis, which occurs in 50 percent of cases of juvenile arthritis, systemic symptoms are minimal. Generally, three or fewer large joints, especially the knee, elbows or ankles, are involved. Chronic iridocyclitis may develop in 30 percent of these patients and there is a high risk of permanent vision impairment.

In the systemic or acutely febrile form of juvenile arthritis, which occurs in 20 percent of cases, systemic symptoms such as spiking fevers, rash and organomegaly often overshadow the articular findings.
Thirty percent of cases of juvenile arthritis involve polyarticular arthritis. Five or more joints are usually involved. Polyarticular arthritis resembles adult RA due to symmetric involvement of the small joints of the hands and feet. The cervical spine can be involved as well. There may be systemic symptoms but they are not as dramatic as one might see in the febrile form of juvenile arthritis.

Laboratory findings include an increased ESR, low-grade anemia and high peripheral WBC count. Rheumatoid factor is rarely demonstrable in children. Early X-rays may show soft tissue swelling and osteoporosis. Treatment may include rest, NSAIDs, DMARDs or systemic or intraarticular steroids.

C. Lyme disease is the correct answer. Lyme disease, a tick-born infection, is caused by the spirochete Borrelia burgdorferi. The infection is transmitted by the nymph stage of the tiny ixodid tick and the majority of infections occur between May and July. In endemic areas, up to 60 percent of ticks may be infected with the spirochete.

The disease was first described in the 1970s when an unusual clustering of arthritis was noted near Lyme, Ct. While the disease is now widespread in the United States, most cases occur in the following three areas: the Northeast from southern Maine through Maryland; the upper Midwest; and northern California and Oregon.
The increased number of cases in recent years is thought to be caused by several factors: the rising deer population; the increasing encroachment of residential areas into previously wooded rural areas; the increased number of ixodid ticks; and improved recognition of the disease.

The infection is divided into three stages, which can overlap.

Stage one occurs three to 30 days after the tick bite. This stage is characterized by the typical erythema migrans (EM) rash. However, in up to 25 percent of cases, EM may be absent or go unnoticed. The rash consists of expanding annular erythema and often has central clearing. The rash may be warm but is usually not painful. Accordingly, it can be easily missed if it is out of sight. At this stage, patients may often experience a flu-like illness with malaise, fatigue, headache, fever, chills, arthralgias and myalgias. Even without EM, this flu-like syndrome is often considered grounds for treatment when it occurs during summer in an endemic area.

In stage two, there is an early disseminated infection that occurs days to weeks after inoculation. The skin, central nervous system or heart may be involved. In 50 percent of patients, secondary skin lesions develop. Four to 10 percent of patients develop cardiac involvement, consisting of atrial or ventricular arrhythmias, heart block or myopericarditis. Neurologic involvement, which may occur in 10 to 20 percent of patients, ranges from Bell’s palsy to meningitis or encephalitis.

In stage three, which can occur weeks to years after the untreated, primary infection, 60 percent of patients develop arthritis that primarily affects large joints, especially the knee. Large effusions are common. Affected joints may be warm but are not often red or painful. Attacks may be recurrent but usually decrease in frequency over time. Joint fluid analysis shows WBC counts of 500 to 100,000; total protein of 3 to 8 gm/liter; and glucose greater than two-thirds that of serum. About 10 percent of patients with arthritis may experience prolonged (over one year) episodes of arthritis.

The diagnosis is based on clinical and laboratory findings. Detection of specific antibodies by Enzyme-Linked ImmunoSorbent Assay (ELISA) is sensitive and specific. Western Blot testing can be confirmatory. One may obtain positive cultures early in the disease.

In regard to early disease, clinicians can treat patients with oral doxycycline, amoxicillin or cefuroxime axetil. When it comes to stages two or three of the disease, clinicians may prescribe either the oral medications mentioned above for four weeks or parenteral penicillin or ceftriaxone for two to four weeks.

Dr. Feld is an Associate Professor at the Drexel University Physician Assistant Program in Philadelphia.

Dr. Auth is a physician assistant and is the Director of the Drexel Hahnemann Physician Assistant Program at Drexel University in Philadelphia.

D. Osgood-Schlatter disease is not the correct answer. Osgood-Schlatter disease, a relatively common cause of knee pain in adolescents, involves painful swelling of the tibial tuberosity. There may be a bony prominence anteriorly at the tibial tubercle. Knee effusions are not characteristic of Osgood-Schlatter disease.

The main symptom is pain at the tibial tubercle, especially with walking, climbing stairs and squatting. These patients may also have increased pain with knee extension against resistance. Lateral X-rays may reveal separation and fragmentation of the upper portion of the tibial tuberosity.

When it comes to this condition, clinicians usually emphasize treatment with ice and NSAIDS, and advise patients to decrease aggravating activity. It usually resolves when the epiphysis closes.

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