NR 511 Week 4 Case Analysis, Acute Knee Swelling Example

Case Analysis: A Hot Right Knee Ten Days After Hernia Surgery in a 71-Year-Old on Hydrochlorothiazide, Where the History Points to Gout, the Radiograph Points to Calcium Pyrophosphate, and Infection Has to Be Excluded First

Student Name

College of Nursing, Chamberlain University

NR 511: Differential Diagnosis and Primary Care Practicum

Instructor Name

Month Day, Year

Case Analysis: A Hot Right Knee Ten Days After Hernia Surgery in a 71-Year-Old on Hydrochlorothiazide, Where the History Points to Gout, the Radiograph Points to Calcium Pyrophosphate, and Infection Has to Be Excluded First

The Case

Mr. H. W. is a 71-year-old retired machinist who calls the clinic because his right knee became hot, swollen and very painful overnight. He can barely bear weight. Ten days ago he had an elective inguinal hernia repair and went home the next day. He takes hydrochlorothiazide 25 mg and lisinopril 20 mg for hypertension and has stage 3a chronic kidney disease; his last kidney panel, in the spring, put his filtration at 52. He drinks three or four beers on Saturday nights. He has never had a swollen joint before, and he denies an injury, a recent sore throat, diarrhea, urinary symptoms or a new sexual partner. There is no knee replacement or prior knee surgery.

On examination his temperature is 37.7 C, heart rate 92 and blood pressure 146/84 mm Hg. The right knee is warm, red over the front and has a large effusion with a positive bulge sign; any movement past about 30 degrees of flexion is too painful. The hernia incision is healing cleanly. No other joint is swollen, and a search of the ear rims, elbows and finger joints finds no tophi. A radiograph of the knee taken in the clinic shows a moderate effusion, mild joint space narrowing and thin linear calcification within the medial and lateral menisci. His serum uric acid today is 8.4 mg/dL. The white blood cell count is 11,200 per microliter and the C-reactive protein is raised.

What Is Established and What Is Assumed

Established: an acute monoarthritis of a large joint in an older man, beginning ten days after surgery, with a low-grade temperature; a raised serum uric acid; meniscal calcification on the radiograph; and two drugs and a drinking pattern that raise uric acid.

Assumed, and not yet safe to assume: that the calcification on the film is the cause of this attack; that the high uric acid is the cause of this attack; and that the joint is not infected. Each of these assumptions would feel natural, and each could be wrong. Calcification of cartilage becomes common with age and many people who have it never have an attack (Rosenthal & Ryan, 2016). A raised uric acid is common in people who never have gout, and during an attack it can even fall into the normal range. A temperature of 37.7 C and a raised white count fit crystal arthritis but fit infection too.

The First Duty: Septic Arthritis

Before comparing the two crystal diagnoses, the analysis has to deal with infection, because a septic joint can destroy cartilage within days and is sometimes fatal in older adults. His age and the recent surgery both raise the prior probability. In a systematic review, Margaretten et al. (2007) found that no feature of the history or examination could reliably exclude septic arthritis and that synovial fluid analysis was required. So neither crystal reading can be accepted until the knee has been aspirated, and no treatment that could mask infection, such as a steroid injection, is given first.

The knee was aspirated in the clinic the same day. The fluid was cloudy and yellow. The synovial white cell count was 18,000 per microliter with 80% neutrophils. In the same review, a count below 25,000 per microliter lowered the likelihood of infection, with a likelihood ratio of 0.32, and a neutrophil fraction below 90% also lowered it (Margaretten et al., 2007). Those numbers pull infection down the list without removing it, so the Gram stain and culture remain part of the decision.

Reading One: Acute Gout

Findings it accounts for: the sudden onset overnight, the intensity of pain and redness, the raised uric acid, two urate-raising drugs, weekend beer and a recent operation, since surgery and the stress around it are recognized triggers of a gout flare.

Findings it fails to account for: this is his first attack and it is in the knee, whereas a first gout flare classically involves the base of the big toe. The meniscal calcification is also unexplained by gout.

What it predicts: needle-shaped crystals that are strongly negatively birefringent under polarized light in the synovial fluid, and a good response to standard flare treatment. It would also predict that, if he has more attacks, some will involve the feet.

Reading Two: Acute Calcium Pyrophosphate Crystal Arthritis

Findings it accounts for: his age, the knee as the joint involved, the meniscal calcification on the radiograph, and the timing after surgery. Rosenthal and Ryan (2016) describe acute calcium pyrophosphate crystal arthritis, the condition once called pseudogout, as most often affecting the knee in older adults and note that attacks can follow surgery or medical illness.

Findings it fails to account for: the raised uric acid, though that does not need to be explained by the knee at all.

What it predicts: rhomboid or rod-shaped crystals that are weakly positively birefringent in the synovial fluid, often fewer and harder to see than urate crystals, and calcification in other joints such as the wrists if they are imaged.

What Tips the Balance

The two readings were held side by side until the laboratory's polarized light examination came back the next morning: weakly positively birefringent rhomboid crystals, many of them inside white cells, and no needle-shaped crystals seen. The Gram stain showed no organisms. On this evidence, acute calcium pyrophosphate crystal arthritis becomes the working diagnosis, and the radiograph finding moves from an incidental observation to supporting evidence.

Two cautions keep the conclusion honest. First, gout and calcium pyrophosphate disease can occur together, and a single sample without urate crystals does not prove he has no gout. His uric acid remains a separate problem worth following. Second, the culture takes 48 hours, and infection is not fully excluded until it is back. A crystal diagnosis and an infection can also coexist.

The Ranked List

1. Acute calcium pyrophosphate crystal arthritis of the right knee: supported by the crystals seen, the joint involved, his age and the radiograph.

2. Septic arthritis: less likely on the synovial count and a negative Gram stain, but kept on the list until the culture is final because of the cost of missing it.

3. Acute gout, alone or coexisting: less likely for this attack, since no urate crystals were seen, but kept because his uric acid, drugs and alcohol leave him at risk.

4. Other causes set aside: reactive arthritis (no preceding diarrheal or urinary infection) and a traumatic effusion (no injury, and the fluid was not bloody).

The Plan That Follows

The plan is built to separate and to treat safely, not to cover every possibility at once. Treatment for the flare is chosen with his kidneys in mind. Nonsteroidal anti-inflammatory drugs are avoided because of his chronic kidney disease and age, and colchicine would need a reduced dose at his kidney function. Once the Gram stain was negative, a short course of oral prednisone was started, and an intra-articular steroid injection is held until the culture is confirmed negative. Rest, ice and a cane for a few days were advised.

Hydrochlorothiazide is a question for the follow-up visit rather than today, since changing a drug during an acute attack confuses the picture; however, a thiazide raises uric acid, and if further evaluation suggests gout, the 2020 American College of Rheumatology guideline supports switching away from it where practical (FitzGerald et al., 2020). His calcium, magnesium, phosphate and thyroid tests will be checked, because calcium pyrophosphate disease can be linked to metabolic conditions such as hyperparathyroidism, particularly in younger patients.

He is to call the same day for rising fever, shaking chills, spreading redness or worsening pain despite the prednisone, any of which would bring infection back to the top of the list. A recheck is booked in three days, when the culture will be final.

References

FitzGerald, J. D., Dalbeth, N., Mikuls, T., Brignardello-Petersen, R., Guyatt, G., Abeles, A. M., Gelber, A. C., Harrold, L. R., Khanna, D., King, C., Levy, G., Libbey, C., Mount, D., Pillinger, M. H., Rosenthal, A., Singh, J. A., Sims, J. E., Smith, B. J., Wenger, N. S., . . . Neogi, T. (2020). 2020 American College of Rheumatology guideline for the management of gout. Arthritis Care & Research, 72(6), 744-760. https://doi.org/10.1002/acr.24180

Margaretten, M. E., Kohlwes, J., Moore, D., & Bent, S. (2007). Does this adult patient have septic arthritis? JAMA, 297(13), 1478-1488. https://doi.org/10.1001/jama.297.13.1478

Rosenthal, A. K., & Ryan, L. M. (2016). Calcium pyrophosphate deposition disease. New England Journal of Medicine, 374(26), 2575-2584. https://doi.org/10.1056/NEJMra1511117