# Diagnostic Radiology/Musculoskeletal Imaging/Joint Disorders/Reiter syndrome

Reiter's Syndrome is an inflammatory spondyloarthropathy, characterized by the classic triad of nongonococcal urethritis, conjunctivitis, and arthritis. The eponym "Reiter's arthritis" has been replaced by the more descriptive terminology reactive arthritis because of Dr Reiter's experiments in Nazi concentration camps.

## Etiology

Reactive arthritis generally occurs about 1 to 3 weeks after a systemic infection. Chlamydia trachomatis is the bacteria most often associated with reactive arthritis, but several different bacteria acquired through the digestive tract, including Salmonella, Shigella, Yersinia, and Campylobacter, are associated with reactive arthritis as well.
Reactive arthritis is usually self-limited, and generally lasts less than 6 months. The disease tends to remit, but recurs intermittently in 35% of cases, and 25% of patients will have chronic low grade symptoms. These recurrences may manifest as only one of the constellation of symptoms seen in the acute attack.
Although the reason why only some people are affected after infection is unclear, the HLA-B27 haplotype has been found to increase a person's chance of developing reactive arthritis. Approximately 80% of people with RS are HLA-B27 positive.

## Clinical Findings

Mild constitutional symptoms generally appear within 1–3 weeks. Urethritis may be postdysenteric or postvenereal. Musculoskeletal symptoms are mainly muscle pains (myalgias), asymmetric joint stiffness in the lower extremities, or low back pain.
A scoring system for diagnosis of reactive arthritis-like spondyloarthropathy exists. Two or more of the following establishes the diagnosis ( one from musculoskeletal system).
* Asymmetric oligoarthritis predominantly of the lower extremity
* Sausage shaped finger (dactylitis), toe, heel pain, or other enthesitis
* Cervicitis or acute diarrhea within one month of arthritis
* Conjunctivitis or iritis
* Genital ulceration or urethritis

## Radiologic Findings

Skeletal abnormalities develop in up to 80% of patients. Initial attacks of pain subside, only to recur later, leaving progressive changes at joints and entheses (sites of musculotendinous insertions). The classic radiographic findings are:
* Normal mineralization (osteoporosis in acute phase)
* Periostitis
* Ill define erosions
* Bilateral asymmetric distribution
* Joint space narrowing
* Fusiform soft tissue swelling
The imaging appearance is similar to psoriatic arthritis. However the distinction is made based on the distribution. Reactive arthritis predominantly involves the lower extremities, primarily the feet, ankles, knees, and sacroiliac joints.

### Feet

Reactive arthritis has a predilection for metatarsophalangeal joints and first IP joint over the distal and proximal interphalangeal joints. The arthritis is initially seen involving one joint only. There may be swelling of the entire digit giving the appearance of a sausage. Early on a periostitis of the phalanges may be noted. Later on uniform joint space narrowing, and marginal erosions with adjacent bone proliferation occur.
Calcaneus is involved in more than 50% of patients, hence the name "lover's heel". Painful erosions and reactive spurs are very common at the attachment sites of Achilles tendon and plantar aponeurosis in calcaneus.

### Ankle

Usually there is fluffy periostitis of tibia and fibula with soft tissue swelling. Uniform joint space loss may occur and erosions are less frequent.

### SI Joint

Bilateral asymmetric involvement is characteristic. Erosive changes are first seen on the iliac side of the true synovial joint. Because of the asymmetry, radiographically it may appear as unilateral involvement and indistinguishable from septic arthritis. However bone scan may show uptake in both SI joints. Ankylosis is less frequent.

### Spine

Involvement is typically around thoracolumbar junction (lower three thoracic or upper three lumbar). Early involvement occurs as paravertebral ossification. As the disease progresses large bulky bony bridges form between adjacent vertebral bodies.

### Differential Diagnosis

Involvement is typically around thoracolumbar junction (lower three thoracic or upper three lumbar). Early involvement occurs as paravertebral ossification. As the disease progresses large bulky bony bridges form between adjacent vertebral bodies.
Sclerosis and ill-definition of both SI joints is noted in this patient with reactive arthritis
Fig. 1 Sclerosis and ill-definition of both SI joints is noted in this patient with reactive arthritis.
Bony proliferation (arrows) is noted along the anterior margin of the lumbar spine in this patient with reactive arthritis
Fig. 2 Bony proliferation (arrows) is noted along the anterior margin of the lumbar spine in this patient with reactive arthritis.
Erosion of the 3rd and 5th metatarsal heads is noted
Fig. 3 Erosion of the 3rd and 5th metatarsal heads is noted.
Prominent erosion of the posterior calcaneus is noted adjacent to the retrocalcaneal bursa
Fig. 4 Prominent erosion of the posterior calcaneus is noted adjacent to the retrocalcaneal bursa.

## Treatment

Three therapies are used in reactive arthritis: NSAIDS for acute inflammation, antibiotics for infection, and sulfasalazine or methotrexate for chronic disease.

## Prognosis

The prognosis for patients with reactive arthritis is generally good. Most people will have complete recovery of the initial illness 2 – 6 months after symptom onset. Approximately 20% of people with reactive arthritis will have mild, chronic symptoms that usually present as back pain and arthritis. There are a small percentage of people who will develop persistent, severe deforming arthritis. For these unfortunate few, treatments are generally not effective.

## References

* Stavropoulos PG, Soura E, Kanelleas A, Katsambas A, Antoniou C. Reactive arthritis. J Eur Acad Dermatol Venereol. 2015 Mar;29(3):415-24. doi: 10.1111/jdv.12741. Epub 2014 Sep 8. PMID: 25199646.
* Hannu T. Reactive arthritis. Best Pract Res Clin Rheumatol. 2011 Jun;25(3):347-57. doi: 10.1016/j.berh.2011.01.018. PMID: 22100285.
* Schmitt SK. Reactive Arthritis. Infect Dis Clin North Am. 2017 Jun;31(2):265-277. doi: 10.1016/j.idc.2017.01.002. Epub 2017 Mar 11. PMID: 28292540.
* García-Kutzbach A, Chacón-Súchite J, García-Ferrer H, Iraheta I. Reactive arthritis: update 2018. Clin Rheumatol. 2018 Apr;37(4):869-874. doi: 10.1007/s10067-018-4022-5. Epub 2018 Feb 17. PMID: 29455267.