Ultrasonography and magnetic resonance imaging of the hands and/or feet have been proposed as useful diagnostic investigations in RS3PE.

Some studies linked RS3PE to HLA-B27 whereas others have not.

RS3PE responds excellently to low dose corticosteroids, with sustained and often complete remission. Non-steroidal anti-inflammatory drugs (NSAIDs) have also been used. Hydroxychloroquine has proven effective in some cases.

Poor prognostic factors include,

- Persistent synovitis

- Early erosive disease

- Extra-articular findings (including subcutaneous rheumatoid nodules)

- Positive serum RF findings

- Positive serum anti-CCP autoantibodies

- Carriership of HLA-DR4 "Shared Epitope" alleles

- Family history of RA

- Poor functional status

- Socioeconomic factors

- Elevated acute phase response (erythrocyte sedimentation rate [ESR], C-reactive protein [CRP])

- Increased clinical severity.

Diagnosis of JIA is difficult because joint pain in children can be from many other causes. No single test can confirm the diagnosis, and most physicians use a combination of blood tests, X-rays, and clinical presentation to make an initial diagnosis of JIA. The blood tests measure antibodies and the rheumatoid factor. Unfortunately, the rheumatoid factor is not present in all children with JIA. Moreover, in some cases, the blood work is somewhat normal. X-rays are obtained to ensure that the joint pain is not from a fracture, cancer, infection, or congenital abnormality.

In most cases, fluid from the joint is aspirated and analyzed. This test often helps in making a diagnosis of JIA by ruling out other causes of joint pain.

RA reduces lifespan on average from three to twelve years. According to the UK's National Rheumatoid Arthritis Society, Young age at onset, long disease duration, the concurrent presence of other health problems (called co-morbidity), and characteristics of severe RA—such as poor functional ability or overall health status, a lot of joint damage on x-rays, the need for hospitalisation or involvement of organs other than the joints—have been shown to associate with higher mortality". Positive responses to treatment may indicate a better prognosis. A 2005 study by the Mayo Clinic noted that RA sufferers suffer a doubled risk of heart disease, independent of other risk factors such as diabetes, alcohol abuse, and elevated cholesterol, blood pressure and body mass index. The mechanism by which RA causes this increased risk remains unknown; the presence of chronic inflammation has been proposed as a contributing factor. It is possible that the use of new biologic drug therapies extend the lifespan of people with RA and reduce the risk and progression of atherosclerosis. This is based on cohort and registry studies, and still remains hypothetical. It is still uncertain whether biologics improve vascular function in RA or not. There was an increase in total cholesterol and HDLc levels and no improvement of the atherogenic index.

There are no set standards for the diagnosis of suspected transient synovitis, so the amount of investigations will depend on the need to exclude other, more serious diseases.

Inflammatory parameters in the blood may be slightly raised (these include erythrocyte sedimentation rate, C-reactive protein and white blood cell count), but raised inflammatory markers are strong predictors of other more serious conditions such as septic arthritis.

X-ray imaging of the hip is most often unremarkable. Subtle radiographic signs include an accentuated pericapsular shadow, widening of the medial joint space, lateral displacement of the femoral epiphyses with surface flattening (Waldenström sign), prominent obturator shadow, diminution of soft tissue planes around the hip joint or slight demineralisation of the proximal femur. The main reason for radiographic examination is to exclude bony lesions such as occult fractures, slipped upper femoral epiphysis or bone tumours (such as osteoid osteoma). An anteroposterior and frog lateral (Lauenstein) view of the pelvis and both hips is advisable.

An ultrasound scan of the hip can easily demonstrate fluid inside the joint capsule (Fabella sign), although this is not always present in transient synovitis. However, it cannot reliably distinguish between septic arthritis and transient synovitis. If septic arthritis needs to be ruled out, needle aspiration of the fluid can be performed under ultrasound guidance. In transient synovitis, the joint fluid will be clear. In septic arthritis, there will be pus in the joint, which can be sent for bacterial culture and antibiotic sensitivity testing.

More advanced imaging techniques can be used if the clinical picture is unclear; the exact role of different imaging modalities remains uncertain. Some studies have demonstrated findings on magnetic resonance imaging (MRI scan) that can differentiate between septic arthritis and transient synovitis (for example, signal intensity of adjacent bone marrow). Skeletal scintigraphy can be entirely normal in transient synovitis, and scintigraphic findings do not distinguish transient synovitis from other joint conditions in children. CT scanning does not appear helpful.

New research shows that identifying what type of JIA a child has can help target treatment and lead to more positive outcomes. Identifying the specific biomarkers related to each type of JIA can help form more personalized treatment plans and decrease remission rates.

Children with JIA are more susceptible to cardiovascular disease, depression, sleep disturbance, anxiety and fatigue than healthy individuals. There is also limited information that suggests that children with JIA are at increased risk for malignancies when being treated with TNF blockers.

Prognosis is more positive when gene testing is undergone to identify what subtype of JIA is present in the child. Standardized treatment protocols are in place specific to each subtype of JIA. Treatment is more successful when targeted to the specific subtype of JIA.

Pain in or around the hip and/or limp in children can be due to a large number of conditions. Septic arthritis (a bacterial infection of the joint) is the most important differential diagnosis, because it can quickly cause irreversible damage to the hip joint. Fever, raised inflammatory markers on blood tests and severe symptoms (inability to bear weight, pronounced muscle guarding) all point to septic arthritis, but a high index of suspicion remains necessary even if these are not present. Osteomyelitis (infection of the bone tissue) can also cause pain and limp.

Bone fractures, such as a toddler's fracture (spiral fracture of the shin bone), can also cause pain and limp, but are uncommon around the hip joint. Soft tissue injuries can be evident when bruises are present. Muscle or ligament injuries can be contracted during heavy physical activity —however, it is important not to miss a slipped upper femoral epiphysis. Avascular necrosis of the femoral head (Legg-Calvé-Perthes disease) typically occurs in children aged 4–8, and is also more common in boys. There may be an effusion on ultrasound, similar to transient synovitis.

Neurological conditions can also present with a limp. If developmental dysplasia of the hip is missed early in life, it can come to attention later in this way. Pain in the groin can also be caused by diseases of the organs in the abdomen (such as a psoas abscess) or by testicular disease. Rarely, there is an underlying rheumatic condition (juvenile idiopathic arthritis, Lyme arthritis, gonococcal arthritis, ...) or bone tumour.

Arthritis mutilans' parent condition psoriatic arthritis leaves people with a mortality risk 60% higher than the general population, with premature death causes mirroring those of the general population, cardiovascular issues being most common. Life expectancy for people with psoriatic arthritis is estimated to be reduced by approximately 3 years.

The bone edema in arthitis mutilans can be treated with TNF inhibitors in the short term: a 2007 study found that the bone edema associated with psoriatic arthritis (of which arthitis mutilans is a subtype) responded to TNF inhibitors with "dramatic" improvement, but the study was not determinative of whether TNF inhibitors would prevent new bone formation, bone fusion, or osteolysis (bone resorption).

Synovitis symptoms can be treated with anti-inflammatory drugs such as NSAIDs. An injection of steroids may be done, directly into the affected joint. Specific treatment depends on the underlying cause of the synovitis.

PVNS is radiologically diagnosed by magnetic resonance imaging (MRI). The disorder is difficult to identify and is often not diagnosed for four years or more after presentation due to nonspecific symptoms or a general paucity of symptoms.

Traditional autonomic testing is used to aid in the diagnosis of AAG. These tests can include a Tilt Table Test (TTT), thermoregulatory sweat test (TST), quantitative sudomotor autonomic reflex testing (QSART) and various blood panels. Additionally, a blood test showing high levels of the antibody ganglionic nicotenic acetylcholine receptor (gAChr) occur in about 50% of patients with AAG (seropositive AAG). The seronegative patients (those without detectable gAChR levels) are theorized to have one or more different antibodies responsible for the autonomic dysfunction. However, both seropositive and seronegative patients have been seen to respond to the same treatments. A paraneoplastic panel may also be ordered to rule out paraneoplastic syndrome.

Once PVNS is confirmed by biopsy of the synovium of an affected joint, a synovectomy of the affected area is the most common treatment. Bone lesions caused by the disorder are removed and bone grafting is performed as needed. Because diffuse PVNS has a relatively high rate of recurrence, radiation therapy may be considered as a treatment option. In some cases, a total joint replacement is needed to relieve symptoms when PVNS causes significant joint destruction.

There is no definitive test to diagnose psoriatic arthritis. Symptoms of psoriatic arthritis may closely resemble other diseases, including rheumatoid arthritis. A rheumatologist (a doctor specializing in autoimmune diseases) may use physical examinations, health history, blood tests and x-rays to accurately diagnose psoriatic arthritis.

Factors that contribute to a diagnosis of psoriatic arthritis include the following:

- Psoriasis in the patient, or a family history of psoriasis or psoriatic arthritis.

- A negative test result for rheumatoid factor, a blood factor associated with rheumatoid arthritis.

- Arthritis symptoms in the distal Interphalangeal articulations of hand (the joints closest to the tips of the fingers). This is not typical of rheumatoid arthritis.

- Ridging or pitting of fingernails or toenails (onycholysis), which is associated with psoriasis and psoriatic arthritis.

- Radiologic images demonstrating degenerative joint changes.

Other symptoms that are more typical of psoriatic arthritis than other forms of arthritis include enthesitis (inflammation in the Achilles tendon (at the back of the heel) or the plantar fascia (bottom of the feet)), and dactylitis (sausage-like swelling of the fingers or toes).

Common clinical signs and symptoms of Whipple's disease include diarrhea, steatorrhea, abdominal pain, weight loss, migratory arthropathy, fever, and neurological symptoms. Weight loss and diarrhea are the most common symptoms that lead to identification of the process, but may be preceded by chronic, unexplained, relapsing episodes of non-destructive seronegative arthritis, often of large joints.

Diagnosis is made by biopsy, usually by duodenal endoscopy, which reveals PAS-positive macrophages in the lamina propria containing non-acid-fast gram-positive bacilli. Immunohistochemical staining for antibodies against "T. whipplei" has been used to detect the organism in a variety of tissues, and a PCR-based assay is also available. PCR can be confirmatory if performed on blood, vitreous fluid, synovial fluid, heart valves, or cerebrospinal fluid. PCR of saliva, gastric or intestinal fluid, and stool specimens is highly sensitive, but not specific enough, indicating that healthy individuals can also harbor the causative bacterium without the manifestation of Whipple's disease, but that a negative PCR is most likely indicative of a healthy individual.

Endoscopy of the duodenum and jejunum can reveal pale yellow shaggy mucosa with erythematous eroded patches in patients with classic intestinal Whipple's disease, and small bowel X-rays may show some thickened folds. Other pathological findings may include enlarged mesenteric lymph nodes, hypercellularity of lamina propria with "foamy macrophages", and a concurrent decreased number of lymphocytes and plasma cells, per high power field view of the biopsy.

A D-Xylose test can be performed, which is where the patient will consume 4.5g of D-xylose, a sugar, by mouth. The urine excretion of D-Xylose is then measured after 5 hours. The majority of D-Xylose is absorbed normally, and should be found in the urine. If the D-Xylose is found to be low in the urine, this suggests an intestinal malabsorption problem such as bacterial overgrowth of the proximal small intestine, Whipple's Disease, or an autoimmune with diseases such as Celiac's Disease (allergy to gluten) or Crohn's Disease (autoimmune disease affecting the small intestine). With empiric antibiotic treatment after an initial positive D-Xylose test, and if a follow-up D-Xylose test is positive (decreased urine excretion) after antibiotic therapy, then this would signify it is not bacterial overgrowth of the proximal small intestine. Since Whipple's disease is so rare, a follow-up positive D-Xylose test more likely indicates a non-infectious etiology and more likely an autoimmune etiology. Clinical correlation is recommended to rule out Whipple's disease.

Assessment of Spondylarthritis International Society (ASAS criteria) is used for classification of axial spondyloarthritis (to be applied for patients with back pain greater than or equal to 3 months and age of onset less than 45 years). It is of two broad types:

1. Sacroiliitis on imaging plus 1 SpA feature, or

2. HLA-B27 plus 2 other SpA features

Sacroiliitis on imaging:

- Active (acute) inflammation on MRI highly suggestive of SpA-associated sacroiliitis and/or

- Definite radiographic sacroiliitis

SpA features:

- Inflammatory back pain

- Arthritis

- Enthesitis

- Anterior uveitis

- Dactylitis

- Psoriasis

- Crohn's disease or ulcerative colitis

- Good response to NSAIDs

- Family history of SpA

- HLA-B27

- Elevated CRP

Scleroderma in pregnancy is a complex situation; it increases the risk to both mother and child. Overall scleroderma is associated with reduced fetal weight for gestational age. The treatment for scleroderma often includes known teratogens such as cyclophosphamide, methotrexate, mycophenolate, etc. and hence careful avoidance of such drugs during pregnancy is advised. In these cases hydroxychloroquine and low-dose corticosteroids might be used for disease control.

AQP4-Ab-negative NMO presents problems for diagnosis. The behavior of the oligoclonal bands respect MS can help to establish a more accurate diagnosis. Oligoclonal bands in NMO are rare and they tend to disappear after the attacks, while in MS they are nearly always present and persistent.

It is important to notice for differential diagnosis that, though uncommon, it is possible to have longitudinal lesions in MS

Other problem for diagnosis is that AQP4ab in MOGab levels can be too low to be detected. Some additional biomarkers have been proposed.

The diagnosis is usually made by tissue biopsy, however this cannot reliably distinguish between the granulomas of OFG and those of Crohn's disease or sarcoidosis. Other causes of granulomatous inflammation are ruled out, such as sarcoidosis,

Crohn's disease, allergic or foreign body reactions and mycobacterial infections.

Seventy percent of people who develop psoriatic arthritis first show signs of psoriasis on the skin, 15 percent develop skin psoriasis and arthritis at the same time, and 15 percent develop skin psoriasis following the onset of psoriatic arthritis.

Psoriatic arthritis can develop in people who have any level severity of psoriatic skin disease, ranging from mild to very severe.

Psoriatic arthritis tends to appear about 10 years after the first signs of psoriasis. For the majority of people, this is between the ages of 30 and 55, but the disease can also affect children. The onset of psoriatic arthritis symptoms before symptoms of skin psoriasis is more common in children than adults.

More than 80% of patients with psoriatic arthritis will have psoriatic nail lesions characterized by nail pitting, separation of the nail from the underlying nail bed, ridging and cracking, or more extremely, loss of the nail itself (onycholysis).

Enthesitis is observed in 30 to 50% of patients and most commonly involves the plantar fascia and Achilles’ tendon, but it may cause pain around the patella, iliac crest, epicondyles,

and supraspinatus insertions

Men and women are equally affected by this condition. Like psoriasis, psoriatic arthritis is more common among Caucasians than African or Asian people.

In addition to tests corresponding to the above findings (such as EMG for neuropathy, CT scan, bone marrow biopsy to detect clonal plasma cells, plasma or serum protein electrophoresis to myeloma proteins, other tests can give abnormal results supporting the diagnosis of POEMS syndrome. These included raised blood levels of VEGF, thrombocytes, and/or erythrocyte parameters.

Bisphosphonate therapy has been suggested as a first-line therapeutic option in many case reports and series.

Treatment with tumor necrosis factor alpha antagonists (TNF inhibitors) have been tried in few patients with limited success. Other drugs that are used in psoriatic arthritis, to which SAPHO syndrome is closely related, have also been used in this condition. They include NSAIDs, corticosteroids, sulfasalazine, methotrexate, ciclosporin and leflunomide.

Some patients have responded to antibiotics. The rationale for their use is that Propionibacterium acnes, a bacterium known for its role in acne, has been isolated from bone biopsies of SAPHO patients.

The diagnosis of POEMS syndrome is based on meeting its two mandatory criteria, meeting at least one of its 3 other major criteria, and meeting at least one of its 6 minor criteria. These criteria are:

- Mandatory major criteria

- Plasma cell dyscrasia: This is evidenced by 1) the presence of a serum myeloma protein, typically an IgG or IgA isotype (occurs in nearly 100% of cases; in >95% of instances the myeloma proteins contain a λ chain that is restricted to either of two V lambda 1 subfamily members viz., IGLV1-40*01 and IGLV1-44*01 (see V lambda family); 2) any, but often a small, increase above the normal value of <1.5% in the percentage of nucleated bone marrow cells that are clonal plasma cells (occurs ~67% of cases); and/or 3) presence of a plasma cell tumor (i.e. plasmacytoma) usually in bone (occurs in ~33% of cases).

- Polyneuropathy: The nerve damage is usually symmetrical, located in distal extremities, and due to the nerve losing its fatty myelin coating and axonal damage. Neurons of the Sensory, motor and autonomic nervous systems are all affected. The typical symptoms are therefore numbness, tingling, and weakness in the feet, later affecting the legs and hands. Pain is unusual, but the weakness may eventually become severe and disabling. The autonomic neuropathy may cause excessive sweating and erectile dysfunction; hormonal changes may also contribute to the latter. It is usually the symptoms of neuropathy which prompt a person with POEMS syndrome to seek medical attention.

- Other major criteria

- Castleman disease: The lymphoproliferative disorder Castleman disease associated with POEMS syndrome is multicentric and occurs in ~15 of cases. It is characterized by a morphology in lymph nodes termed angiofollicular lymph node hyperplasia; an overly activate immune system; excessive production of cytokines including particularly IL-6 and to lesser extents, proliferation of immune B cells and T cells, enlarged lymph nodes, enlarged liver and spleen, capillary leak syndrome, anasarca, evidence of extravascular fluid overload, and organ failure. Patients with Castleman disease without a plasma cell dyscrasia and peripheral neuropathy but having other signs and symptoms of POEMS syndrome can be classified as a Castleman disease variant of POEMS syndrome.

- Sclerotic bone lesions: These lesions consist of plasma cell tumors encased within or associated with abnormally dense bone structures; in different studies, they have been observed to occur in 27% to 97% of cases.

- Elevated VEGF: VEGF is a cytokine that stimulates angiogenesis (i.e. capillary formation), increases capillary permeability, and contributes to polyneuropathy. It is elevated in almost all cases of POEMS syndrome and has become a clinically useful marker for the syndrome's presence, severity, and response to treatment. However, its role in mediating the symptoms of this disease are unclear. A second cytokine, IL-12, is similar to VEGF in being highly correlated with the disease activity level in POEMS syndrome.

- Minor criteria

- Organomegaly: Enlargement spleen, liver, and/or lymph nodes occurs in 45% to 85% of cases.

- Extravascular volume overload: Ascites, pleural effusions, pericardial effusions, and/or lower extremity edema occur in 27% to 89% of cases.

- Endocrinopathy: Gynecomastia occurs in 12% to 18% of cases; endocrine abnormalities involving the regulation of gonadotrophins, adrenal gland corticosteroids, and prolactin occur in 55% to 89%, 16% to 33%, and 55 to 20% of cases, respectively. Diabetes and hypothyroidism also occur in 3% to 36% and 9% to 67%, respectively, of cases but are not considered to be criteria for the presence of POEMS syndrome because of their frequent occurrence in the general population.

- Skin changes: Skin changes occur in 68% to 89% of POEMS syndrome patients. These changes most commonly are hyperpigmentation and/or hypertrichosis (abnormal amount of hair growth over the body) but less commonly include glomeruloid hemangioma, signs or symptoms of Hypervolemia (e.g. edema and ascites), acrocyanosis (blue discoloration of the extremities due to blood flow abnormalities), flushing, and/or white nails.

- Papilledema: Papilledema (swelling of retinal optical discs) occurs in 29% to 64% of cases. Papilledema in POEMS syndrome patients may occur with or without visual disturbances, increased intracranial pressure, or changes in cerebral spinal fluid protein levels.

- Thrombocytosis/polycythemia: Thrombocytosis (increase in blood platelet count) and polycythemia (increase in red blood cells) occurs 54% to 88% and 12% to 19%, respectively, of POEMS syndrome patients and may be may underlying causes of these patients to experience thrombosis events.

Treatment of rheumatoid nodules is rarely a priority for people with rheumatoid arthritis. However, surgical removal is often successful, even if there is a tendency for nodules to regrow. Of the drug therapies commonly used in rheumatoid arthritis, methotrexate has the disadvantage of tending to make nodules worse. TNF inhibitors do not have a very reliable effect on nodules. B cell depletion with rituximab often leads to disappearance of nodules but this is not guaranteed.