Mrs. K is a 75-year-old woman who complains of a painful left knee.
|What is the differential diagnosis of joint pain? How would you frame the differential?|
The causes of joint pain range from common to rare and from not particularly dangerous to joint- and life-threatening. Even the most benign causes of joint pain can lead to serious disability. The evaluation of a patient with joint pain calls for a detailed history and physical exam (often focusing on extra-articular findings) and occasionally the sampling of joint fluid and possibly analyzing serologic tests.
There are three pivotal features in organizing the approach to joint pain. First, is the pain articular or extra-articular? Although this distinction may seem obvious, abnormalities of periarticular structures can mimic articular disease. Second, is a single joint or are multiple joints involved? Finally, are the involved joints inflamed or not?
The first pivotal point in making a diagnosis in a patient with joint pain is to determine whether the patient's pain is truly articular, real joint pain, or periarticular.
The differential diagnosis below is organized by these pivotal points: the number of joints involved (monoarticular vs polyarticular) and by whether or not the joint is inflamed (judged by physical exam, joint fluid analysis, or both). Recognize that all of the monoarticular arthritides can present in a polyarticular distribution, and classically polyarticular diseases may occasionally only affect a single joint.
|The joint distribution of diseases that cause joint pain is variable; monoarticular arthritides may present with polyarticular findings and vice versa.|
Nongonococcal septic arthritis
Monosodium urate (gout)
Calcium pyrophosphate dihydrate deposition disease (CPPD or pseudogout)
Rheumatoid arthritis (RA)
Systemic lupus erythematosus (SLE)
Other rheumatic diseases
Mrs. K's symptoms started after she stepped down from a bus with unusual force. The pain became intolerable within about 6 hours of onset and has been present for 3 days now. She otherwise feels well. She reports no fevers, chills, dietary changes, or sick contacts.
On physical exam she is in obvious pain, limping into the exam room on a cane. Her vital signs are temperature, 37.0°C; RR, 12 breaths per minute; BP, 110/70 mm Hg; pulse, 80 bpm. The only abnormality on exam is the right knee. It is red, warm to the touch, and tender to palpation. The range of motion is limited to only about 20 degrees.
|At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?|
Pivotal points in this case are that the patient's symptoms clearly localize to articular, rather than periarticular structures since the exam reveals an inflamed joint with limited range of motion. Therefore, the differential diagnosis focuses primarily on the causes of inflammatory monoarticular arthritis, such as septic arthritis, gout, pseudogout, and trauma.
Salient points of the patient's presentation are the rapid onset of the pain; the mild, antecedent trauma; and the lack of systemic symptoms, such as fever, fatigue, or weight loss.
Given the patient's age, the single inflamed joint, and high incidence of gout, this diagnosis is the leading hypothesis. CPPD (also called pseudogout) is common in the knee of elderly patients, so this must also be high in the differential diagnosis. Traumatic injury to the knee, such as a meniscal injury or intra-articular fracture, are probably less likely given the mild nature of the injury and the inflammation of the joint.
An infectious arthritis is probably less likely, given the sudden onset and lack of systemic symptoms, but are must not miss hypotheses since they are potentially disastrous if left untreated. Gonococcal and nongonococcal septic arthritis are possibilities. Lyme disease can affect multiple joints but most commonly causes a monoarticular arthritis of the knee. Table 23–1 lists the differential diagnosis.
Table 23–1. Diagnostic Hypotheses for Mrs. K.
| Save Table
Table 23–1. Diagnostic Hypotheses for Mrs. K.
|Diagnostic Hypotheses||Clinical Clues||Important Tests|
Involvement of first
|Classic presentation or demonstration of sodium urate crystals in synovial fluid|
|CPPD (pseudogout)||May present as chronic or acute arthritis||Demonstration of crystals in synovial fluid or classic radiographic findings|
|Active Alternative—Must Not Miss|
|Bacterial arthritis (gonococcal or nongonococcal)||Fever with monoarticular or polyarticular arthritis||Positive synovial (or other body) fluid cultures|
Exposure to endemic area
History of tick bite
Response to treatment
|Traumatic injury||Usually history of severe trauma||Appropriate imaging (radiograph for fracture, MRI for cartilaginous injury)|
Mrs. K has never had a similar episode before. Her other medical problems include diabetes with diabetic nephropathy, hypertension, and hypercholesterolemia. Her medications are insulin, enalapril, atorvastatin, and hydrochlorothiazide. There is no history of alcohol or drug abuse.
|Is the clinical information sufficient to make a diagnosis? If not, what other information do you need?|
Gout classically presents in older patients with acute and severe pain of the great toe. The pain generally begins acutely and becomes unbearable within hours of onset. Patients often say that they are not even able to place a bed sheet over the toe. On physical exam, the first metatarsophalangeal (MTP) joint is warm, swollen, ...