Although a 2011 research article stated that disagreements between hand surgeons and rheumatologists remain regarding the indications, timing and effectiveness of rheumatoid hand surgery, arthritis mutilans may be successfully treated by iliac-bone graft and arthrodesis of the interphalangeal joints and the metacarpophalangeal joint in each finger.

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).

Enthesitis is inflammation of the entheses, the sites where tendons or ligaments insert into the bone. It is also called enthesopathy, or any pathologic condition involving the entheses. The entheses are any point of attachment of skeletal muscles to the bone, where recurring stress or inflammatory autoimmune disease can cause inflammation or occasionally fibrosis and calcification. One of the primary entheses involved in inflammatory autoimmune disease is at the heel, particularly the Achilles tendon.

It is associated with HLA B27 arthropathies like ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. Symptoms include multiple points of tenderness at the heel, tibial tuberosity, iliac crest, and other tendon insertion sites.

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.

In 1984, a joint effort led to the definition of specific classification criteria for ankylosing spondylitis, called the “Modified New York Criteria”. One of the central New York criteria was the existence of radiographically visible changes in the sacroiliac joints and/or spine, which have formed due to bone fusion, erosion and/or formation caused by the disease. Even though these criteria helped to improve uniformly define ankylosing spondylitis, such radiologic changes often only manifested several years after the first disease symptoms appeared. In order to be able to study also patients with early and less typical forms, new criteria were needed that could identify the disease already at an early stage. In 2009 the Modified New York criteria were extended by a broad set of new classification criteria that aimed to classify patients based on the presence of typical spondyloarthritis disease features. These included inflammatory back pain, family history for axial spondyloarthritis, response to treatment with nonsteroidal anti-inflammatory drugs (NSAIDs), past history of or current inflammation in the joints (arthritis), tendon-bone attachment of the heel (enthesitis), or eyes (uveitis), bowel (inflammatory bowel disease), skin (psoriasis) or signs of elevated inflammation (C-reactive protein and erythrocyte sedimentation rate. Important parts of the ASAS axSpA criteria is the biomarker HLA-B27 and magnetic resonance imaging (MRI). The criteria can only be applied in people that have chronic back pain (at least 3 months duration) started before the age of 45 years and only in those patients that already have a diagnosis of axial SpA. Since the disease ankylosing spondylitis was still defined by the Modified New York criteria of 1984, there was the need to find a new disease term that would also include the less severe forms or early onset of ankylosing spondylitis. This expression was found in the umbrella term axial spondyloarthritis. The 2009 classification criteria are called the ASAS (Assessment of SpondyloArthritis international Society) axial spondayloarthritis criteria.

Although there are no definitive criteria to diagnose the existence of reactive arthritis, the American College of Rheumatology has published sensitivity and specificity guidelines.

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

There are few clinical symptoms, but the clinical picture is dominated by arthritis in one or more joints, resulting in pain, swelling, redness, and heat sensation in the affected areas.

The urethra, cervix and the throat may be swabbed in an attempt to culture the causative organisms. Cultures may also be carried out on urine and stool samples or on fluid obtained by arthrocentesis.

Tests for C-reactive protein and erythrocyte sedimentation rate are non-specific tests that can be done to corroborate the diagnosis of the syndrome.

A blood test for the genetic marker HLA-B27 may also be performed. About 75 percent of all the patients with Reiter's arthritis have this gene.

Worldwide prevalence of spondyloarthropathy is approximately 1.9%.

Axial spondyloarthritis can be divided into two classes:

1. Non-radiographic axial spondyloarthritis (nr-axSpA): This term encompasses both, the early disease stage of ankylosing spondylitis, in which no radiographic changes are visible yet, as well as less severe forms of ankylosing spondylitis.

2. Radiographic axial spondyloarthritis:Synonym for ankylosing spondylitis. This class is termed radiographic axial spondyloarthritis due to the unambiguous diagnosis through radiographic changes in the sacroiliac joints and/or spine.

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).

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.

Some doctors include two other, less common forms: enthesitis-related arthritis and psoriatic JIA. Enthesitis is an inflammation of the insertion points of the tendons. This form occurs most often in boys older than 8, large joints of lower extremities are commonly affected; characteristically, it causes back pain, and is linked to ankylosing spondylitis and inflammatory bowel disease. Psoriatic JIA occurs most often in girls, in conjunction with psoriasis or any two of these features - i.e. dactylitit and nail pitting, although joint problems may precede the skin manifestations by several years.

In medicine, an enthesopathy refers to a disorder involving the attachment of a tendon or ligament to a bone. This site of attachment is known as the entheses.

If the condition is known to be inflammatory, it can more precisely be called an enthesitis.

Enthesopathies may take the form of spondyloarthropathies (joint diseases of the spine) such as ankylosing spondylitis, plantar fasciitis, and Achilles tendinitis. Enthesopathy can occur at the elbow, wrist, carpus, hip, knee, ankle, tarsus, or heel bone, among other regions. Further examples include:

- Adhesive capsulitis of shoulder

- Rotator cuff syndrome of shoulder and allied disorders

- Periarthritis of shoulder

- Scapulohumeral fibrositis

- Synovitis of hand or wrist

- Periarthritis of wrist

- Gluteal tendinitis

- Iliac crest spur

- Psoas tendinitis

- Trochanteric tendinitis

Diagnosis includes dilated fundus examination to rule out posterior uveitis, which presents with white spots across the retina along with retinitis and vasculitis.

Laboratory testing is usually used to diagnose specific underlying diseases, including rheumatologic tests (e.g. antinuclear antibody, rheumatoid factor, angiotensin converting enzyme inhibitor <-- error) and serology for infectious diseases (Syphilis, Toxoplasmosis, Tuberculosis).

Major histocompatibility antigen testing may be performed to investigate genetic susceptibility to uveitis. The most common antigens include HLA-B27, HLA-A29 (in birdshot chorioretinopathy) and HLA-B51 (in Behçet disease).

Radiology X-ray may be used to show coexisting arthritis and chest X-ray may be helpful in sarcoidosis.

Diagnosis of sarcoidosis is a matter of exclusion, as there is no specific test for the condition. To exclude sarcoidosis in a case presenting with pulmonary symptoms might involve a chest radiograph, CT scan of chest, PET scan, CT-guided biopsy, mediastinoscopy, open lung biopsy, bronchoscopy with biopsy, endobronchial ultrasound, and endoscopic ultrasound with fine-needle aspiration of mediastinal lymph nodes (EBUS FNA). Tissue from biopsy of lymph nodes is subjected to both flow cytometry to rule out cancer and special stains (acid fast bacilli stain and Gömöri methenamine silver stain) to rule out microorganisms and fungi.

Serum markers of sarcoidosis, include: serum amyloid A, soluble interleukin-2 receptor, lysozyme, angiotensin converting enzyme, and the glycoprotein KL-6. Angiotensin-converting enzyme blood levels are used in the monitoring of sarcoidosis. A bronchoalveolar lavage can show an elevated (of at least 3.5) CD4/CD8 T cell ratio, which is indicative (but not proof) of pulmonary sarcoidosis. In at least one study the induced sputum ratio of CD4/CD8 and level of TNF was correlated to those in the lavage fluid. A sarcoidosis-like lung disease called granulomatous–lymphocytic interstitial lung disease can be seen in patients with common variable immunodeficiency (CVID) and therefore serum antibody levels should be measured to exclude CVID.

Differential diagnosis includes metastatic disease, lymphoma, septic emboli, rheumatoid nodules, granulomatosis with polyangiitis, varicella infection, tuberculosis, and atypical infections, such as "Mycobacterium avium" complex, cytomegalovirus, and cryptococcus. Sarcoidosis is confused most commonly with neoplastic diseases, such as lymphoma, or with disorders characterized also by a mononuclear cell granulomatous inflammatory process, such as the mycobacterial and fungal disorders.

Chest radiograph changes are divided into four stages:

1. bihilar lymphadenopathy

2. bihilar lymphadenopathy and reticulonodular infiltrates

3. bilateral pulmonary infiltrates

4. fibrocystic sarcoidosis typically with upward hilar retraction, cystic and bullous changes

Although people with stage 1 radiographs tend to have the acute or subacute, reversible form of the disease, those with stages 2 and 3 often have the chronic, progressive disease; these patterns do not represent consecutive "stages" of sarcoidosis. Thus, except for epidemiologic purposes, this categorization is mostly of historic interest.

In sarcoidosis presenting in the Caucasian population, hilar adenopathy and erythema nodosum are the most common initial symptoms. In this population, a biopsy of the gastrocnemius muscle is a useful tool in correctly diagnosing the person. The presence of a noncaseating epithelioid granuloma in a gastrocnemius specimen is definitive evidence of sarcoidosis, as other tuberculoid and fungal diseases extremely rarely present histologically in this muscle.

Sarcoidosis may be divided into the following types:

- Annular sarcoidosis

- Erythrodermic sarcoidosis

- Ichthyosiform sarcoidosis

- Hypopigmented sarcoidosis

- Löfgren syndrome

- Lupus pernio

- Morpheaform sarcoidosis

- Mucosal sarcoidosis

- Neurosarcoidosis

- Papular sarcoid

- Scar sarcoid

- Subcutaneous sarcoidosis

- Systemic sarcoidosis

- Ulcerative sarcoidosis

The prognosis is generally good for those who receive prompt diagnosis and treatment, but serious complication including cataracts, glaucoma, band keratopathy, macular edema and permanent vision loss may result if left untreated. The type of uveitis, as well as its severity, duration, and responsiveness to treatment or any associated illnesses, all factor into the outlook.

A complete blood count may reveal anemia, which commonly is caused by blood loss leading to iron deficiency (a microcytic anemia) or by vitamin B deficiency (a macrocytic anemia), usually caused by ileal disease impairing vitamin B absorption. Rarely autoimmune hemolysis may occur. Ferritin levels help assess if iron deficiency is contributing to the anemia. Erythrocyte sedimentation rate (ESR) and C-reactive protein help assess the degree of inflammation, which is important as ferritin can also be raised in inflammation. Serum iron, total iron binding capacity and transferrin saturation may be more easily interpreted in inflammation. Anemia of chronic disease results in a normocytic anemia. Other causes of anemia include medication used in treatment of inflammatory bowel disease, like azathioprine, which can lead to cytopenia, and sulfasalazine, which can also result in folate deficiency. Testing for "Saccharomyces cerevisiae" antibodies (ASCA) and antineutrophil cytoplasmic antibodies (ANCA) has been evaluated to identify inflammatory diseases of the intestine and to differentiate Crohn's disease from ulcerative colitis. Furthermore, increasing amounts and levels of serological antibodies such as ASCA, antilaminaribioside [Glc(β1,3)Glb(β); ALCA], antichitobioside [GlcNAc(β1,4)GlcNAc(β); ACCA], antimannobioside [Man(α1,3)Man(α)AMCA], antiLaminarin [(Glc(β1,3))3n(Glc(β1,6))n; anti-L] and antichitin [GlcNAc(β1,4)n; anti-C] associate with disease behavior and surgery, and may aid in the prognosis of Crohn's disease.

Low serum levels of vitamin D are associated with Crohn's disease. Further studies are required to determine the significance of this association.

The most common disease that mimics the symptoms of Crohn's disease is ulcerative colitis, as both are inflammatory bowel diseases that can affect the colon with similar symptoms. It is important to differentiate these diseases, since the course of the diseases and treatments may be different. In some cases, however, it may not be possible to tell the difference, in which case the disease is classified as indeterminate colitis.