Reactive arthritis (formerly known as Reiter disease) is usually associated with conjunctivitis and urethritis. It is a disease predominantly of males between 15 and 35 years of age and is transmitted through either epidemic dysentery or sexual intercourse. The arthritis may be present without documentation of the other clinical manifestations. In such cases, radiographic examination may provide the appropriate diagnosis. The classic radiographic features are as follows:
- 1.
Fusiform soft tissue swelling
- 2.
Early juxta-articular osteoporosis; reestablishment of normal mineralization
- 3.
Uniform joint space loss
- 4.
Bone proliferation
- 5.
Ill-defined erosions
- 6.
Bilateral asymmetrical distribution
- 7.
Distribution primarily in feet, ankles, knees, and sacroiliac (SI) joints; hands, hips, and spine less frequently involved
Although the specific radiographic changes are identical to those of psoriatic arthritis, reactive arthritis has a characteristic but different distribution, thus allowing for accurate differential diagnosis.
The feet
The small articulations of the foot and the calcaneus are the most frequently involved joints in reactive arthritis. The arthritis is initially seen involving one joint only ( Fig. 11-1 ). This monoarticular involvement could lead to a misdiagnosis of septic arthritis; therefore, the observation of the aggressiveness of the changes plays an important role in correct interpretation. There may be swelling of the entire digit (dactylitis), giving it an appearance of a sausage or cocktail hot dog. Early in the disease, juxta-articular osteoporosis is present and persists for a longer period of time than it does in psoriasis. Eventually normal mineralization returns. Early, a periostitis may be observed along the shafts of the phalanges ( Fig. 11-2 ). Later, uniform joint space loss and marginal erosions with adjacent bone proliferation occur ( Fig. 11-3 ). These changes are indistinguishable from the changes of psoriatic arthritis in the toes. Ankylosis of the joints does not occur as frequently as it does in psoriatic arthritis. Reactive arthritis also seems to prefer the metatarsophalangeal (MTP) joints ( Fig. 11-4 ) and first interphalangeal (IP) joint over the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints seen classically in psoriatic arthritis.
The calcaneus is involved in more than 50 percent of patients with reactive arthritis. Often it may be the only bone ever involved; hence the name “lover’s heel.” As in psoriatic arthritis, there is erosion and bone production at the attachment of the Achilles tendon and the plantar aponeurosis. Ill-defined spurs may develop at the aponeurotic attachment more frequently than at the Achilles tendon attachment ( Fig. 11-5 ). They will tend to point upward and parallel the undersurface of the calcaneus ( Fig. 11-6 ). Bone formation on the surface of the tarsal bones indicates midfoot involvement ( Fig. 11-7 ).
