Diagnosis is fourfold: History and physical examination, elevation of creatine kinase, electromyograph (EMG) alteration, and a positive muscle biopsy.

The hallmark clinical feature of polymyositis is proximal muscle weakness, with less important findings being muscle pain and dysphagia. Cardiac and pulmonary findings will be present in approximately 25% of cases of patients with polymyositis.

Sporadic inclusion body myositis (sIBM): IBM is often confused with (misdiagnosed as) polymyositis or dermatomyositis that does not respond to treatment is likely IBM. sIBM comes on over months to years; polymyositis comes on over weeks to months. Polymyositis tends to respond well to treatment, at least initially; IBM does not.

Proximal muscle weakness, characteristic skin rash and elevated muscle enzymes are routinely used to identify JDM. Typical magnetic resonance imaging and muscle biopsy changes are considered the next most useful diagnostic criteria, followed by myopathic changes on electromyogram, calcinosis, dysphonia and nailfold capillaroscopy. Other useful criteria include myositis-specific or -related antibodies, nailfold capillaroscopy, factor VIII-related antigen, muscle ultrasound, calcinosis and neopterin.

Elevated creatine kinase (CK) levels in the blood (at most ~10 times normal) are typical in sIBM but affected individuals can also present with normal CK levels. Electromyography (EMG) studies usually display abnormalities. Muscle biopsy may display several common findings including; inflammatory cells invading muscle cells, vacuolar degeneration, inclusions or plaques of abnormal proteins. sIBM is a challenge to the pathologist and even with a biopsy, diagnosis can be ambiguous.

A diagnosis of inclusion body myositis was historically dependent on muscle biopsy results. Antibodies to cytoplasmic 5'-nucleotidase (cN1A; NT5C1A) have been strongly associated with the condition. In the clinical context of a classic history and positive antibodies, a muscle biopsy might be unnecessary.

IBM is often initially misdiagnosed as polymyositis. A course of prednisone is typically completed with no improvement and eventually sIBM is confirmed. sIBM weakness comes on over months or years and progresses steadily, whereas polymyositis has an onset of weeks or months. Other forms of muscular dystrophy (e.g. limb girdle) must be considered as well.

There are a number of known causes of myopathy, and it is only once these have been ruled out that a clinician will assign an idiopathic inflammatory myopathy (IIM) syndrome to a case. The usual criteria for a diagnosis of PM are weakness in muscles of the head, neck, trunk, upper arms or upper legs; raised blood serum concentrations of some muscle enzymes such as creatine kinase; unhealthy muscle changes on electromyography; and biopsy findings of (i) muscle cell degeneration and regeneration and (ii) chronic inflammatory infiltrates in muscle cells. If heliotrope (purple) rash or Gottron's papules are also present, then the diagnosis is DM. In DM, myositis may not be clinically apparent but detectable via biopsy or MRI. If the criteria for PM are met but muscle weakness also affects the hands and feet or is not accompanied by pain IBM should be suspected, and confirmed when muscle cell biopsy reveals (i) cytoplasmic vacuoles fringed by basophilic granules and (ii) inflammatory infiltrate comprising mostly CD8 T lymphocytes and macrophages; and electron microscopy reveals filamentous inclusions in both cytoplasm and nucleus.

There is no specific test for this condition. Diagnosis is based on signs and symptoms, and exclusion of other conditions.

Polymyositis, like dermatomyositis, strikes females with greater frequency than males.

Computed tomography (CT) findings in AIP include a "diffusely enlarged hypodense" pancreas or a focal mass that may be mistaken for a pancreatic malignancy. A low-density, "capsule-like rim on CT" (possibly corresponding to an inflammatory process involving peripancreatic tissues) is thought to be an additional characteristic feature (thus the mnemonic: "sausage-shaped"). Magnetic resonance imaging (MRI) reveals a diffusely decreased signal intensity and delayed enhancement on dynamic scanning. The characteristic ERCP finding is segmental or diffuse irregular narrowing of the main pancreatic duct, usually accompanied by an extrinsic-appearing stricture of the distal bile duct. Changes in the extrapancreatic bile duct similar to those of primary sclerosing cholangitis (PSC) have been reported.

The role of endoscopic ultrasound (EUS) and EUS-guided fine-needle aspiration (EUS-FNA) in the diagnosis of AIP is not well described, and EUS findings have been described in only a small number of patients. In one study, EUS revealed a diffusely swollen and hypoechoic pancreas in 8 of the 14 (57%) patients, and a solitary, focal, irregular mass was observed in 6 (46%) patients. Whereas EUS-FNA is sensitive and specific for the diagnosis of pancreatic malignancy, its role in the diagnosis of AIP remains unclear.

Despite its very similar clinical presentation to PM, IBM does not respond to the drugs that effectively treat PM, and there is no proven effective therapy for IBM. Alemtuzumab is being studied but as of May 2013 it had not demonstrated clinical effectiveness in IBM. Dysphagia (difficulty swallowing) may be improved by intravenous immunoglobulin, though more trials are needed. Non-fatiguing, systematic strength-building exercise has demonstrated benefit. Occupational and rehabilitation therapists can offer good advice on walking without falling and performing fine motor tasks, and can provide appropriate canes, braces and wheelchairs. Speech pathologists can provide advice on preventing choking episodes and reducing the anxiety of an immanent aspiration for both patients and carers.

Most recently the fourteenth Congress of the International Association of Pancreatology developed the International Consensus Diagnostic Criteria (ICDC) for AIP. The ICDC emphasizes five cardinal features of AIP which includes the imaging appearance of pancreatic parenchyma and the pancreatic duct, serum IgG4 level, other organ involvement with IgG4-related disease, pancreatic histology and response to steroid therapy.

In 2002, the Japanese Pancreas Society proposed the following diagnostic criteria for autoimmune pancreatitis:

For diagnosis, criterion I (pancreatic imaging) must be present with criterion II (laboratory data) and/or III (histopathologic findings).

Mayo Clinic has come up with five diagnostic criteria called HISORt criteria which stands for histology, imaging, serology, other organ involvement, and response to steroid therapy.

The best imaging modality for idiopathic orbital inflammatory disease is contrast-enhanced thin section magnetic resonance with fat suppression. The best diagnostic clue is a poorly marginated, mass-like enhancing soft tissue involving any area of the orbit.

Overall, radiographic features for idiopathic orbital inflammatory syndrome vary widely. They include inflammation of the extraocular muscles (myositis) with tendinous involvement, orbital fat stranding, lacrimal gland inflammation and enlargement (dacryoadenitis), involvement of the optic sheath complex, uvea, and sclera, a focal intraorbital mass or even diffuse orbital involvement. Bone destruction and intracranial extension is rare, but has been reported. Depending on the area of involvement, IOI may be categorized as:

- Myositic

- Lacrimal

- Anterior – Involvement of the globe, retrobulbar orbit

- Diffuse – Multifocal intraconal involvement with or without an extraconal component

- Apical – Involving the orbital apex and with intracranial involvement

Tolosa–Hunt syndrome is a variant of orbital pseudotumor in which there is extension into the cavernous sinus through the superior orbital fissure. Another disease variant is Sclerosing pseudotumor, which more often presents bilaterally and may extend into the sinuses.

CT findings

In non-enhanced CT one may observe a lacrimal, extra-ocular muscle, or other orbital mass. It may be focal or infiltrative and will have poorly circumscribed soft tissue. In contrast-enhanced CT there is moderate diffuse irregularity and enhancement of the involved structures. A dynamic CT will show an attenuation increase in the late phase, contrary to lymphoma where there is an attenuation decrease. Bone CT will rarely show bone remodeling or erosion, as mentioned above.

MR findings

On MR examination there is hypointensity in T1 weighted imaging (WI), particularly in sclerosing disease. T1WI with contrast will show moderate to marked diffuse irregularity and enhancement of involved structures. T2 weighted imaging with fat suppression will show iso- or slight hyperintensity compared to muscle. There is also decreased signal intensity compared to most orbital lesions due to cellular infiltrate and fibrosis. In chronic disease or sclerosing variant, T2WI with FS will show hypointensity (due to fibrosis). Findings on STIR (Short T1 Inversion Recovery) are similar to those on T2WI FS. In Tolosa–Hunt syndrome, findings include enhancement and fullness of the anterior cavernous sinus and superior orbital fissure in T1WI with contrast, while MRA may show narrowing of cavernous sinus internal carotid artery (ICA).

Ultrasonographic findings

On grayscale ultrasound there is reduced reflectivity, regular internal echoes, and weak attenuation, in a way, similar to lymphoproliferative lesions.

At least one study suggests that gluten neuropathy can be effectively treated with a gluten-free diet. In the study, 35 patients with gluten neuropathy adhered to a gluten-free diet, where adherence was monitored serologically. After one year, the treatment group had improved significantly compared to the control group. The indicators of improvements were improvements of sural sensory action potential and subjective improvement of neuropathic symptoms. Subgroup analysis suggested that severe neuropathy might imply reduced capacity for recovery of the peripheral nerves or longer recovery.

A diagnostic test for statin-associated auto-immune necrotizing myopathy will be available soon in order to differentiate between different types of myopathies during diagnosis. The presence of abnormal spontaneous electrical activity in the resting muscles indicates an irritable myopathy and is postulated to reflect the presence of an active necrotising myopathic process or unstable muscle membrane potential. However, this finding has poor sensitivity and specificity for predicting the presence of an inflammatory myopathy on biopsy. Further research into this spontaneous electrical activity will allow for a more accurate differential diagnosis between the different myopathies.

Currently a muscle biopsy remains a critical test, unless the diagnosis can be secured by genetic testing. Genetic testing is a less invasive test and if it can be improved upon that would be ideal. Molecular genetic testing is now available for many of the more common metabolic myopathies and muscular dystrophies. These tests are costly and are thus best used to confirm rather than screen for a diagnosis of a specific myopathy. Due to the cost of these tests, they are best used to confirm rather than screen for a diagnosis of a specific myopathy. It is the hope of researchers that as these testing methods improve in function, both costs and access will become more manageable

The increased study of muscle pathophysiology is of importance to researchers as it helps to better differentiate inflammatory versus non-inflammatory and to aim treatment as part of the differential diagnosis. Certainly classification schemes that better define the wide range of myopathies will help clinicians to gain a better understanding of how to think about these patients. Continued research efforts to help appreciate the pathophysiology will improve clinicians ability to administer the most appropriate therapy based on the particular variety of myopathy.

The mechanism for myopathy in individuals with low vitamin D is not completely understood. A decreased availability of 250HD leads to mishandling of cellular calcium transport to the sarcoplasmic reticulum and mitochondria, and is associated with reduced actomyosin content of myofibrils.

Of the children diagnosed with and treated for JDM, about half will recover completely. Close to 30 percent will have weakness after the disease resolves. Most children will go into remission and have their medications eliminated within two years, while others may take longer to respond or have more severe symptoms that take longer to clear up.

A common lasting effect of JDM is childhood arthritis.

A patient's history is one of the key factors in diagnosing acquired noninflammatory myopathy. The history is used not only to analyze the time frame with which the patient began to express symptoms, but to also see if the disease is within the patient's family's history, to check medication or drug use history, and to see if the patient has suffered any trauma due to illness or infection. Basic exams will test for where the muscle weakness is and how weak it is. This is performed by testing for proximal and distal muscle strength, as well as testing for any signs of neurogenic symptoms such as impaired sensation, deep tendon reflexes, and atrophy.

If needed, more advanced equipment can be used to help determine whether a patient is suffering from ANIM. This includes:

- Measurement of serum levels of muscle enzymes

- Electromyography (EMG)

- Magnetic Resonance Imaging (MRI)

- Muscle biopsy

When examining the serum levels of muscle enzymes, the relative levels of creatine kinase, aldolase, aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase are closely examined. Abnormal levels of these proteins are indicative of both inflammatory myopathy and ANIM.

EMGs are particularly useful in locating the affected muscle groups, as well as determining the distribution of the myopathy throughout the cell. EMGs measure several indicators of myopathies such as:

- The spontaneous electrical movement from a single muscle fiber at rest,

- Measurement of a polyphasic, shorter amplitude, motor unit action potential during muscle stimulation,

- Determining that the muscle group cannot differentiate large motor plate stimulation from small motor plate stimulation involved in recruitment of muscle fibers.

Magnetic Resonance Imaging will elicit edema in inflammatory patients, but it will most likely show nothing in patients with ANIM and if it does, it will show some atrophy.

If an individual's ANIM is a result of a metabolite defect, then additional tests are required. These tests are directed at enzyme function at rest and during exercise, and enzyme intermediates. Molecular genetic testing is often used to determine if there was any predisposition to the expressed symptoms.

The diagnosis of retroperitoneal fibrosis cannot be made on the basis of results of laboratory studies. CT is the best diagnostic modality: a confluent mass surrounding the aorta can be seen on a CT scan. Although biopsy is not usually recommended, it is appropriate when malignancy or infection is suspected. Biopsy should also be done if the location of fibrosis is atypical or if there is an inadequate response to initial treatment.

Polymyositis and dermatomyositis are first treated with high doses of a corticosteroids

Once established, periods of remissions and relapse can persist indefinitely.

While IH may remit spontaneously for most people the condition is long-lasting. Treatments as described above can be effective in reducing the frequency and degree of effusions. Deformative changes to joints are not a common feature of this mostly non-inflammatory condition.

Corticosteroids remain the main treatment modality for IOI. There is usually a dramatic response to this treatment and is often viewed as pathognomonic for this disease. Although response is usually quick, many agree that corticosteroids should be continued on a tapering basis to avoid breakthrough inflammation.

Although many respond to corticosteroid treatment alone, there are several cases in which adjuvant therapy is needed. While many alternatives are available, there is no particular well-established protocol to guide adjuvant therapy. Among the available options there is: surgery, alternative corticosteroid delivery, radiation therapy, non-steroidal anti-inflammatory drugs, cytotoxic agents (chlorambucil, cyclophosphamide), corticosteroid sparing immunosuppressants (methotrexate, cyclosporine, azathioprine), IV immune-globin, plasmapheresis, and biologic treatments (such as TNF-α inhibitors).

Diagnosis of gluten-sensitive neuropathies without a clear cause is on the rise. These "idiopathic" neuropathies were first identified by screening for anti-gliadin IgG (AGA). The criteria have been critiqued because of the large misdiagnosis rate of coeliac disease (CD), and because AGA exists in the normal population at over 12%, far more abundant than cases of neuropathy. The problem in diagnosis arises because there are precursor states prior to coeliac disease. These are called coeliac disease and early gluten-sensitive enteropathy and are defined as Marsh grade 1 and 2 coeliac disease. Coeliac disease was diagnosed by duodenal biopsy, often misinterpreted as negative as high as grade 3 on the Marsh scale. Anti-gliadin antibodies may precede or lag the appearance of coeliac disease. Studies in Scandinavia found an increase of pathologies as much as 10 years before coeliac disease. These included gastrointestinal symptoms, anemia or other autoimmune disease. In addition IgG and IgA responses sometimes accompany allergic responses to proteins. Gliadin is exceptional in that it has several proteins which remain peptides of considerable length after digestion, and migrate into systemic circulation.

A subset of people with idiopathic neuropathies have only anti-gliadin antibodies but none of the other enteropathic criteria. About 1/3 have no DQ2 or DQ8 and an apparent abundance of HLA-DQ1. One percent of coeliacs in Europe have no DQ2 and DQ8 but have DQ1. The DQ1 serotype is very common in the normal population, over 65% of Americans have one copy, therefore the linkage is speculative.

Erythema nodosum is diagnosed clinically. A biopsy can be taken and examined microscopically to confirm an uncertain diagnosis. Microscopic examination usually reveals a neutrophilic infiltrate surrounding capillaries that results in septal thickening, with fibrotic changes in the fat around blood vessels. A characteristic microscopic finding is radial granulomas, well-defined nodular aggregates of histiocytes surrounding a stellate cleft.

Additional evaluation should be performed to determine the underlying cause of erythema nodosum. This may include a full blood count, erythrocyte sedimentation rate (ESR), antistreptolysin-O (ASO) titer and throat culture, urinalysis, intradermal tuberculin test, and a chest x-ray. The ESR is typically high, the C-reactive protein elevated, and the blood showing an increase in white blood cells.

The ESR is initially very high, and falls as the nodules of erythema nodosum. The ASO titer is high in cases associated with a streptococcal throat infection. A chest X-ray should be performed to rule out pulmonary diseases, in particular sarcoidosis and Löfgren syndrome.

Studies show a moderate neutrophilia (less than 50%), elevated ESR (greater than 30 mm/h) (90%), and a slight increase in alkaline phosphatase (83%). Skin biopsy shows a papillary and mid-dermal mixed infiltrate of polymorphonuclear leukocytes with nuclear fragmentation and histiocytic cells. The infiltrate is predominantly perivascular with endothelial-cell swelling in some vessels, but vasculitic changes (blood clots; deposition of fibrin, complement, or immunoglobulins within the vessel walls; red blood cell extravasation;inflammatory infiltration of vascular walls) are absent in early lesions.

Perivasculitis occurs secondarily, because of cytokines released by the lesional neutrophils. True transmural vasculitis is not an expected finding histopathologically in SS.

Adenocarcinoma of the bowel has been associated with coeliac disease.

Periodic fever syndromes (also known as autoinflammatory diseases or autoinflammatory syndromes) are a set of disorders characterized by recurrent episodes of systemic and organ-specific inflammation. Unlike autoimmune disorders such as systemic lupus erythematosus, in which the disease is caused by abnormalities of the adaptive immune system, patients with autoinflammatory diseases do not produce autoantibodies or antigen-specific T or B cells. Instead, the autoinflammatory diseases are characterized by errors in the innate immune system.

The syndromes are diverse, but tend to cause episodes of fever, joint pains, skin rashes, abdominal pains and may lead to chronic complications such as amyloidosis.

Most autoinflammatory diseases are genetic and present during childhood. The most common genetic autoinflammatory syndrome is familial Mediterranean fever, which causes short episodes of fever, abdominal pain, serositis, lasting less than 72 hours. It is caused by mutations in the MEFV gene, which codes for the protein pyrin.

Pyrin is a protein normally present in the inflammasome. The mutated pyrin protein is thought to cause inappropriate activation of the inflammasome, leading to release of the pro-inflammatory cytokine IL-1β. Most other autoinflammatory diseases also cause disease by inappropriate release of IL-1β. Thus, IL-1β has become a common therapeutic target, and medications such as anakinra, rilonacept, and canakinumab have revolutionized the treatment of autoinflammatory diseases.

However, there are some autoinflammatory diseases that are not known to have a clear genetic cause. This includes PFAPA, which is the most common autoinflammatory disease seen in children, characterized by episodes of fever, aphthous stomatitis, pharyngitis, and cervical adenitis. Other autoinflammatory diseases that do not have clear genetic causes include adult-onset Still's disease, systemic-onset juvenile idiopathic arthritis, Schnitzler syndrome, and chronic recurrent multifocal osteomyelitis. It is likely that these diseases are multifactorial, with genes that make people susceptible to these diseases, but they require an additional environmental factor to trigger the disease.

Another example that shows that autoinflamatory conditions may not be genetic in origin is found in a report published in "Nature" which shows that diet is very important in the development of such diseases. The ingestion levels of highly saturated fats and cholesterol, (high fat diet, HFD) affects the microbiota composition of the gut. Changes in the microbiota induced by a HFD are protective against the susceptibility to develop osteomyelitis (autoimmune disease) as compared with the changes induced by a low-fat diet. The changes in the microbiome of individuals under HFD showed a reduction in "Prevotella" abundance and were accompanied by significantly reduced expression levels of pro-Interleukin-1β in distant neutrophils.

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.