Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 50-year-old man is evaluated for a left lower extremity ulcer. He has a 15-year history of worsening arthritis for which he has never been evaluated. He takes ibuprofen as needed.

On physical examination, vital signs are normal. The spleen tip is palpable. There is swelling of multiple small joints at the hands, knees, and metatarsophalangeal (MTP) joints. There is ulnar deviation and subluxation of the metacarpophalangeal joints. Subcutaneous nodules are present at the elbows bilaterally. There is a 2- × 2-cm shallow ulcer at the medial left lower extremity just above the ankle.

Laboratory studies:

Hematocrit	33%
Leukocyte count	2100/µL (2.1 × 109/L), with 900 neutrophils
Platelet count	276,000/µL (276 × 109/L)
Urinalysis	Normal

Which of the following is the most likely diagnosis?

A. AA amyloidosis
B. Felty syndrome
C. Sarcoidosis
D. Systemic lupus erythematosus

MKSAP Answer and Critique

The correct answer is B. Felty syndrome.

The most likely diagnosis is Felty syndrome, which consists of the triad of long-standing aggressive rheumatoid arthritis (RA), neutropenia, and splenomegaly. Patients with Felty syndrome are almost always seropositive. This patient has the typical findings of long-standing RA, including involvement of multiple small joints of the hands and feet, joint subluxation, and subcutaneous nodules. Felty syndrome is associated with the risk for serious infections, lower extremity ulcers, lymphoma, and vasculitis. Treatment of Felty syndrome consists of more aggressive therapy for the underlying RA.

AA amyloid results from accumulation of the AA protein, an acute phase reactant seen in chronic inflammatory diseases. Although AA amyloidosis can be associated with hepatosplenomegaly, the most common organ involved in AA amyloidosis is the kidney and is evidenced by heavy proteinuria. Hematologic abnormalities may include anemia as the result of chronic kidney disease and thrombocytopenia secondary to splenomegaly, but neutropenia is unusual. AA amyloidosis cannot account for this patient’s joint findings or lower extremity ulcer.

Sarcoidosis most commonly affects the lungs. Severe sarcoidosis can uncommonly be associated with a chronic arthritis that is typically polyarticular, involving the shoulders, hands, wrists, knees, and ankles, and often coexists with lung and cutaneous sarcoidosis. An entire digit may be affected, leading to dactylitis. Sarcoidosis can also be associated with slightly tender subcutaneous nodules of the upper extremities and (rarely) splenomegaly. Sarcoidosis does not cause leukopenia or cutaneous ulcers and is an unlikely cause of this patient’s findings.

Joint involvement occurs in 90% of patients with systemic lupus erythematosus (SLE), with inflammatory polyarthralgia the most common presentation. Frank arthritis occurs in 40% of patients with SLE. Both small and large joints can be affected. Persistent periarticular inflammation can damage soft-tissue structures that support joints, resulting in reducible subluxation of the digits, swan neck deformities, and ulnar deviation (Jaccoud arthropathy). All three bone marrow cell lines can be affected in SLE. Leukopenia occurs in 50% of patients, with lymphopenia predominating. Subcutaneous nodules are not usually found in SLE. In addition, up to 90% of patients with SLE have skin (acute, subacute, or chronic lupus) or mucous membrane involvement. The presence of splenomegaly and subcutaneous nodules and absence of skin rash argue against the diagnosis of SLE. In addition, serologies would help distinguish RA from SLE.

Key Point

• Felty syndrome consists of the triad of long-standing aggressive rheumatoid arthritis, neutropenia, and splenomegaly and is associated with the risk for serious infections, lower extremity ulcers, lymphoma, and vasculitis.

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