When Joint Pain Isn't What It Seems: Rheumatological Conditions Disguised as Musculoskeletal Pain

The single most important warning sign that something other than a musculoskeletal injury is happening is inflammation and swelling that cannot be attributed to anything. No clear mechanism, no obvious overload, no recent change in training or work, no impact event — and yet the joint or tendon is hot, swollen, stiff, or painful in ways that do not match what you would expect from injury.

Physiotherapists see this more often than people realise. The musculoskeletal system is the front door for a long list of rheumatological conditions. Painful knuckles. A swollen finger. Heel pain that will not settle. Lower back stiffness that is worse in the morning and eases with movement. All of these can look like an injury, a tendinopathy, or wear-and-tear — until you look more carefully at the pattern.

This blog walks through the rheumatological conditions most commonly mistaken for musculoskeletal problems: rheumatoid arthritis, the spondyloarthropathies, psoriatic arthritis, inflammatory back pain, and the two crystal arthropathies (gout and pseudogout). For each one, we cover the pattern that distinguishes it, the clinical tools your physiotherapist uses to screen for it, and what early identification means for your long-term outcomes.

Rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease in which the immune system attacks the synovium — the thin layer of tissue that lines the inside of a joint capsule.⁴ The result is synovitis, an inflammatory reaction inside the joint that causes pain, swelling, stiffness, and over time, joint damage. The same process can affect the tendon sheath (tenosynovitis), which is one reason that RA sometimes first presents as what looks like a tendon problem.

The classic pattern is symmetrical and small-joint dominant. Most people first notice it in the knuckles — the MCP and PIP joints of the hands — and the bases of the toes (the MTP joints). Typically five or more joints are involved, on both sides of the body, with morning stiffness lasting more than an hour.⁴⁵ A unilateral painful knuckle from a knock is not RA. Both index fingers swollen and stiff in the morning for a few weeks, in someone with no obvious trigger, might be.

Australian numbers

In 2022, around 514,000 Australians (2.0% of the population) were estimated to be living with RA, affecting 2.5% of women and 1.6% of men.¹² Onset most frequently occurs between the ages of 35 and 64. By 2040, age-standardised rates in Australia are forecast to rise to 1.75% in men and 2.94% in women.³ It is a disease that is becoming more common, not less.

The female-to-male ratio of around 1.6 to 1 is consistent with international data, where the disparity is largely explained by higher prevalence and greater disease burden in older women.³

What can be modified

RA is autoimmune. It is not caused by lifestyle. But the underlying inflammatory environment is influenced by a handful of factors that have meaningful effects on disease activity and outcomes:

Smoking is the most consistently established environmental risk factor for RA, increases the severity of established disease, and reduces the effectiveness of disease modifying drugs. Stopping smoking is the single most impactful lifestyle change for someone with RA or a strong family history.⁵
Diet patterns higher in vegetables, fish, olive oil and whole grains (broadly, a Mediterranean pattern) are associated with lower disease activity in RA cohorts.
Sleep is profoundly modifiable and strongly affects pain, fatigue and inflammatory markers. Poor sleep amplifies inflammatory burden.
Alcohol in excess interacts with several RA medications and influences inflammatory pathways. Moderation matters.
Regular exercise reduces stiffness, maintains function, supports cardiovascular health (cardiovascular disease is the leading cause of premature death in RA), and is now considered first-line management alongside medical care.

These same principles apply across all the inflammatory rheumatological conditions discussed below. The medical management belongs with your GP and rheumatologist; the lifestyle and exercise pillars are where physiotherapy adds value.

The spondyloarthropathies

The spondyloarthropathies are a family of related inflammatory conditions that share several features: they are largely seronegative (rheumatoid factor and anti-CCP negative), they have a strong association with the HLA-B27 gene, they target the enthesis (the site where a tendon, ligament, or joint capsule attaches to bone), and they have a tendency to cause new bone formation rather than just bone destruction.

The two main subgroups are:

Axial spondyloarthritis (axSpA): primarily affecting the spine and sacroiliac joints. This is the modern umbrella term for what older texts called ankylosing spondylitis (now considered the radiographic form of axSpA) and non-radiographic axSpA.
Peripheral spondyloarthritis: primarily affecting peripheral joints, entheses, and digits, with less spinal involvement. Includes psoriatic arthritis, reactive arthritis, and the arthritis associated with inflammatory bowel disease.

The defining feature is that inflammation centres on the enthesis rather than the synovium. Over time, the body responds by laying down new bone at these inflamed sites — a process called ossification. In axSpA, repeated cycles of enthesitis and ossification can lead to the eventual fusion of vertebrae, which is the basis for the older “ankylosing” terminology.

We will cover axSpA in detail in a follow-up blog. For this article, the most useful thing to know is that not every “tendinopathy” that doesn't settle with appropriate loading is actually a tendinopathy. If a patient with what looks like patellar, Achilles, hamstring, or plantar fascia pain is not responding to load management, the question is whether the underlying pathology might be enthesitis driven by a spondyloarthropathy.

The SCREEND’EM tool

Paul Kirwan and colleagues at the Royal College of Surgeons in Ireland published the SCREEND'EM mnemonic in 2019 as a clinical screening tool for spondyloarthropathy in patients presenting with tendinopathy.⁶ It is not a diagnostic test — it is a structured set of questions designed to flag patients who warrant further investigation.

The SCREEND'EM mnemonic for screening tendinopathy patients for spondyloarthropathy: Skin, Colitis or Crohn's, Relatives, Early morning stiffness, Eyes (uveitis), Nail involvement, Dactylitis, Enthesopathy, Medication and Movement response

SCREEND'EM mnemonic adapted from Kirwan, March & Duffy (2019).

The more boxes a patient ticks, the higher the suspicion. A single tick in isolation rarely means much. Three or four positive items in someone with non-resolving tendinopathy is a referral conversation with the GP.

The SPADE tool

The Spondyloarthritis Diagnosis Evaluation tool, available at spadetool.co.uk, is an online calculator developed by Dr Raj Sengupta and colleagues, based on earlier work by Rudwaleit and Feldtkeller.⁷ A clinician enters the clinical features present in a patient under 45 with chronic back pain and no definitive X-ray changes, and the tool returns a probability that the patient has axial spondyloarthritis, along with guidance on the next step.

It is a useful adjunct for primary care and physiotherapy because the average diagnostic delay in axSpA remains in the order of 7 to 10 years globally. The lost time is irreversible.

Psoriatic arthritis

Psoriatic arthritis (PsA) is the inflammatory arthritis associated with psoriasis. It is the most common of the peripheral spondyloarthropathies, affecting between 20% and 30% of people with psoriasis.¹⁰

The peak age of onset is between 30 and 50 years, with most sources placing it in the 40 to 50 year range, and men and women are affected approximately equally.¹⁰¹¹ This is in contrast to RA, which has a clear female predominance.

The typical joint pattern

Where RA is symmetrical and polyarticular (five or more joints), PsA is asymmetric and oligoarticular — typically fewer than five joints, on different sides of the body, and often involving larger peripheral joints like the knee or ankle alongside the smaller joints of the hands or feet.

The hallmark joints to watch for are the distal interphalangeal (DIP) joints — the ones closest to the fingernail. Isolated DIP arthritis in the absence of osteoarthritis is a strong clue for PsA. It also commonly involves the knees and ankles.¹¹

The other near-pathognomonic feature is dactylitis, often called “sausage digits” — uniform swelling of an entire finger or toe, rather than just one joint. Dactylitis is rare in conditions other than PsA, so it is one of the most useful single signs in differential diagnosis.¹¹

Joints vs skin: the order matters

A common assumption is that joint problems precede the skin findings in PsA. The evidence points the other way. Dermatological psoriasis precedes the arthritis in approximately 65% of cases (range 60 to 70%), the two appear simultaneously in around 15 to 20%, and joint disease precedes skin findings in only about 15 to 20% of patients.¹⁰

That means in most people with PsA, there is a history of psoriasis that may be very mild, or hidden in places people do not routinely show their physiotherapist or GP — the scalp (often dismissed as dandruff), behind the ears, the intergluteal cleft, the umbilicus, or under the nails. Nail involvement is present in around 80% of people with PsA, compared with 20% of people with uncomplicated psoriasis.¹¹

The take-home: when a patient has unexplained inflammatory-pattern joint or tendon pain, particularly with dactylitis or DIP involvement, asking about skin and nails — and asking to see them — is one of the most important steps a physiotherapist can take.

Enthesitis vs insertional tendinopathy

One of the diagnostic challenges in PsA is distinguishing enthesitis (inflammation at the tendon insertion driven by a spondyloarthropathy) from insertional tendinopathy (mechanical overload at the same anatomical site). Clinically they can look similar — pain and tenderness at the heel insertion of the Achilles, for example.

Ultrasound is the practical differentiator. Enthesitis typically shows hypoechogenicity, thickening, increased vascularity on Doppler, and adjacent bursitis. Insertional tendinopathy shows changes confined to the tendon itself without the surrounding inflammatory features. The distinction matters because the management is entirely different: progressive loading is the cornerstone of insertional tendinopathy management, whereas enthesitis driven by a spondyloarthropathy needs systemic medical treatment alongside any physiotherapy.

Inflammatory back pain

Back pain is one of the most common reasons people see a physiotherapist. The vast majority is mechanical. But around 5% of chronic back pain cases are inflammatory in origin — and these are the cases that most need to be picked up early.

The criteria most widely used today are the ASAS criteria for inflammatory back pain.⁸⁹ A patient is considered to have inflammatory back pain when four out of the following five features are present:

Age of onset under 40 to 45 years.
Insidious onset — no specific incident or moment when it started.
Improvement with exercise, worsening with rest. This is the inverse of mechanical back pain. Patients with inflammatory back pain feel better as they warm up and worse if they sit still for too long.
Morning stiffness lasting more than 30 minutes, and often considerably longer.
Night pain that wakes the patient in the second half of the night.

The night pain pattern has a physiological explanation. Cortisol is the body's endogenous anti-inflammatory, and it follows a circadian rhythm that bottoms out in the early hours of the morning. As cortisol falls, the inflammatory cytokines that drive joint inflammation rise. The result is that someone with inflammatory back pain is most uncomfortable between 2am and 5am — the very time mechanical back pain is usually quietest.

One other feature worth flagging: alternating buttock pain is a common presentation of sacroiliitis (inflammation of the sacroiliac joint), which is one of the earliest findings in axial spondyloarthritis. Patients often describe a deep gluteal ache that switches sides over weeks or months, and it gets dismissed as muscular or referred pain.

Why this matters: the average delay between symptom onset and diagnosis in axial spondyloarthritis is between 7 and 10 years, and longer in women. Most of this delay happens at the primary care and physiotherapy level, because mechanical back pain is so common that inflammatory back pain gets buried in it. Knowing the pattern, and asking the right questions, is how we change that.

Gout and pseudogout

The two crystal arthropathies present dramatically and are sometimes misdiagnosed as cellulitis, septic arthritis, or musculoskeletal trauma. Both involve crystals depositing in or around a joint and triggering an intense inflammatory response.

Gout

Gout is caused by monosodium urate crystals depositing in joint tissue. The body has too much uric acid in the bloodstream (hyperuricaemia), and at low temperatures or in specific microenvironments, uric acid drops out of solution into crystals. The body recognises the crystals as a foreign body and mounts an inflammatory reaction.¹²

The classic presentation is sudden onset, usually at night, in the big toe MTP joint. The pain is severe enough that bedsheets feel intolerable. The joint is hot, red, swollen, and exquisitely tender. Untreated, an episode lasts around a week. With treatment, it settles much faster.

Although there is a strong genetic component to gout risk, lifestyle factors meaningfully affect frequency: excess alcohol (particularly beer and spirits), high consumption of red meat and seafood, sugar-sweetened beverages high in fructose, and dehydration all raise serum uric acid. Reducing these is part of long-term management alongside urate-lowering medication where indicated.

Pseudogout

Pseudogout is also a crystal arthropathy, but the crystal is different. It is caused by calcium pyrophosphate dihydrate (CPPD) crystals depositing in cartilage and surrounding tissue.¹³ The two conditions can look similar acutely, but the differences matter:

Joint pattern: pseudogout most commonly affects the knee, then the wrist, then the shoulder and ankle. The big toe is much less commonly involved than in gout.
Demographics: pseudogout is overwhelmingly a disease of older adults, with prevalence rising sharply over the age of 65.
Imaging: CPPD deposits show up on X-ray as fine calcium lines within the cartilage (chondrocalcinosis), but importantly, these radiographic findings do not correlate well with symptoms. Plenty of older adults have chondrocalcinosis on imaging and have never had a pseudogout flare. The diagnosis is clinical and ideally confirmed by joint aspiration when there is doubt.

The practical implication for physiotherapy is to keep both on the differential when an older patient presents with an acutely swollen, painful joint with no clear mechanical cause.

A short note on psoriasis

Because psoriatic arthritis is so closely tied to psoriasis, it is worth understanding what the underlying skin condition actually is. Psoriasis is a chronic autoimmune condition in which the immune system, particularly the IL-17 and IL-23 inflammatory pathways, mistakenly triggers rapid turnover of skin cells. Normal skin cells take around 28 days to mature and shed. In a psoriatic plaque, that cycle is compressed to 3 to 5 days. The result is a build-up of immature cells that forms the characteristic raised, red, scaly plaques.

It affects approximately 2 to 4% of adults in Western populations. Plaque psoriasis is the most common form, with lesions classically on the extensor surfaces of the elbows and knees, but psoriasis can show up in many places that are easy to miss: the scalp, behind the ears, in the intergluteal cleft, in the umbilicus, on the palms and soles, and under the fingernails (as pitting or onycholysis). A history of any of these — even mild or intermittent — in a patient with unexplained inflammatory joint or tendon pain is a meaningful piece of information.

When to think rheumatological

None of the patterns described above is diagnostic on its own. But certain combinations of features should prompt a closer look:

Joint or tendon pain with visible swelling that cannot be explained by a recent injury, overload, or impact event.
Morning stiffness lasting more than 30 to 60 minutes, particularly when it eases with movement.
Symmetrical small-joint involvement (knuckles or toes on both sides).
An entire finger or toe swollen rather than a single joint (dactylitis).
A tendinopathy that is not responding to appropriate loading, especially with any of the SCREEND'EM features.
Back pain under 45 that improves with exercise and worsens with rest, with night waking in the second half of the night.
A personal or family history of psoriasis, inflammatory bowel disease, uveitis, or inflammatory arthritis.
A sudden, severe, hot, swollen single joint without a clear mechanism — particularly in the big toe overnight (gout), or knee or wrist in an older patient (pseudogout).

Any of these warrant a referral conversation with your GP. The role of your physiotherapist is to recognise the patterns, communicate them clearly, and continue to provide exercise and lifestyle support alongside whatever medical management is needed.

The bottom line

The musculoskeletal system is the entry point for a wider group of inflammatory conditions than most people realise. Most joint and tendon pain is mechanical and responds well to appropriate physiotherapy. A meaningful minority is not. The cost of missing the difference — particularly in axial spondyloarthritis, where average diagnostic delay still runs to nearly a decade — is joint damage that could have been prevented.

The most important warning sign remains the simplest one: inflammation and swelling that cannot be attributed to anything. Take it seriously, look at the pattern around it, and ask the right next set of questions.