28 May 2020
Rheumatology Reasoning: demystifying the profession
Welcome to the latest edition of Rheumatology Reasoning, by Dr Andrew Jordan.
My aim is to present a common case and work through the reasoning of why I order each test, what questions are most useful to help diagnose this condition and a simple approach to management. The approach is practical and based upon experience and evidence (where it exists). I hope you will find it useful in your day to day practice.
A 53-year old male with a past history of hypertension and impaired glucose tolerance presents with a 15 year history of multiple joints pains. Despite visits to multiple doctors and physiotherapists, a unifying diagnosis has never been made. He has bilateral elbow pain, worse when gripping with the hand. He has right knee pain with difficulty climbing stairs. He reports intermittent knee swelling. He has right shoulder pain with overhead activities. He has pain in his low back in the mornings with about 15 minutes of morning stiffness. He has a 2 year history of psoriasis, mostly affecting his torso. There has been no scalp or nail involvement and he uses intermittent topical ointments. For many years he has been taking Diclofenac 50mg bd to help control his pain.
Examination shows tenderness at both lateral epicondyles with increasing pain on wrist extension, consistent with lateral epicondylitis. Schober’s test is normal. There is patellofemoral crepitus but no knee effusion at the time of my examination. Shoulder range of movement is slightly restricted in a global fashion. There is no palpable synovitis in the peripheral joints.
Psoriatic arthritis is top of the list of differential diagnoses. The presence of both axial and peripheral symptoms is more suggestive of spondyloarthritis (such as psoriatic arthritis) than rheumatoid arthritis. An alternative explanation could be a range of biomechanical abnormalities and degenerative changes. There is a 30% lifetime chance of developing psoriatic arthritis if a patient has skin psoriasis. This risk increases to 50% with scalp psoriasis and 80% with psoriatic nail involvement. The presence of psoriasis is thus a major clue when assessing a patient with joint pains or inflammatory back pain.
It is generally accepted that the enthesis is the main site of inflammation in psoriatic arthritis. The enthesis is the site where ligaments, tendons and joint capsules attach to bone. If there is considerable inflammation at the enthesis, the inflammation may “spill-over” into the synovium and cause joint swelling. This is different to rheumatoid arthritis where the synovium is the main site of inflammation. In clinical practice, this has an impact on how some people present. Rheumatoid arthritis will typically have joint swelling. Early or low-grade psoriatic arthritis may have little in the way of joint swelling, but patients may have grumbling arthralgias which may vary in intensity and location. There may be spinal symptoms with morning stiffness. There are multiple entheses in the spine as there is numerous ligament attachments throughout the spine. The clinical history should also ask about enthesitis – the classic ones are the Achilles tendon insertion, plantar fascia insertion and lateral or medial epicondylar pain.
Blood tests which show normal CRP and ESR. HLA-B27 is negative. RF and CCP antibodies are negative. X-rays of the sacroiliac joint (given the mild inflammatory back pain) are negative. X-rays of the knee show mild medial and patellofemoral compartment osteoarthritis.
At this stage, I feel the main diagnosis is likely to be entheseal inflammation from psoriatic arthritis in combination with early osteoarthritis in his knees. I rely a lot on clinical history. ESR and CRP are frequently not raised with low grade entheseal pain, so normal tests do not alter my clinical suspicion.
NSAIDs are a good initial treatment for enthesitis, so I use this in combination with physiotherapy and exercise physiology to improve his lower limb and shoulder biomechanics.
He didn’t improve much over the subsequent six months and he develops Achilles tendon pain.
I wanted to have some further evidence that my clinical suspicions of enthesitis is correct, so I feel imaging is warranted. A dedicated musculoskeletal ultrasound is performed. It noted cortical irregularity and enthesitis at both lateral epicondyles and right Achilles tendon enthesopathy. Ultrasound is highly user-dependent and assessing entheses is not part of routine musculoskeletal ultrasound practice. It is vital that the ultrasound is performed by someone who is skilled in rheumatology-specific ultrasound.
It now seems clear that he has active psoriatic arthritis. Methotrexate is started, titrating to a dose of 20mg weekly. There is little data for using methotrexate for enthesitis, but options are limited as he was not responding to NSAIDs. Methotrexate has the added advantage of treating psoriasis.
He has an excellent response and over the subsequent months his elbow pain reduced to its lowest level in years! The Achilles tendinopathy also resolved slowly and his skin cleared.
Five years after being on methotrexate he developed hand pain and morning stiffness lasting more than two hours. The CRP and ESR was checked but the levels did not increase. The history of prolonged morning stiffness is typical of inflammatory join pain. His therapy was increased to include leflunomide 10mg daily. His liver function tests were closely monitored as there is a at least a 20% incidence of abnormal LFT’s with the combination of methotrexate and leflunomide, and this rate is higher with psoriatic arthritis than in rheumatoid arthritis (presumably due to the higher rates of metabolic syndrome / fatty liver in psoriatic arthritis). He responded well to combination therapy and morning stiffness reduced to less that 15 minutes in duration. He continues to be in clinical remission.
This case illustrates the importance of relying on clinical history and accepting that CRP and ESR are often a poor guide to inflammation in spondyloarthritis. It is important to be on high alert for arthritis and enthesitis in anyone with psoriasis, given the high lifetime incidence of co-existing disease.
Dr Andrew Jordan writes a regular email to educate interested GPs and allied health professionals.