IOI or orbital pseudotumor is the second most common cause of exophthalmos following Grave’s orbitopathy and the third most common orbital disorder following thyroid orbitopathy and lymphoproliferative disease accounting for 5–17.6% of orbital disorders, There is no age, sex, or race predilection, but it is most frequently seen in middle-aged individuals. Pediatric cases account for about 17% of all cases of IOI.

The exact cause of IOI is unknown, but infectious and immune-mediated mechanisms have been proposed. Several studies have described cases where onset of orbital pseudotumor was seen simultaneously or several weeks after upper respiratory infections. Another study by Wirostko et al. proposes that organisms resembling Mollicutes cause orbital inflammation by destroying the cytoplasmic organelles of parasitized cells.

Orbital pseudotumor has also been observed in association with Crohn’s disease, systemic lupus erythematosus, rheumatoid arthritis, diabetes mellitus, myasthenia gravis, and ankylosing spondylitis all of which strengthen the basis of IOI being an immune-mediated disease. Response to corticosteroid treatment and immunosuppressive agents also support this idea.

Trauma has also been seen to precede some cases of orbital pseudotumor. However, one study by Mottow-Lippe, Jakobiec, and Smith suggests that the release of circulating antigens caused by local vascular permeability triggers an inflammatory cascade in the affected tissues.

Although these mechanisms have been postulated as possible causes of IOI, their exact nature and relationships to the condition still remain unclear.

IgG4-related ophthalmic disease (IgG4-ROD) is the recommended term to describe orbital (eye socket) manifestations of the systemic condition IgG4-related disease, which is characterised by infiltration of lymphocytes and plasma cells and subsequent fibrosis in involved structures. It can involve one or more of the orbital structures.

Frequently involved structures include the lacrimal glands, extraocular muscles, infraorbital nerve, supraorbital nerve and eyelids. It has also been speculated that ligneous conjunctivitis may be a manifestation of IgG4-related disease (IgG4-RD).

As is the case with other manifestations of IgG4-related disease, a prompt response to steroid therapy is a characteristic feature of IgG4-ROD in most cases, unless significant fibrosis has already occurred.

The cause is currently unknown. The histology is suggestive of an autoimmune reaction. The high rate of relapses as well as relatively high proportion of bilateral cases is highly suggestive of a systemic predisposition.

Presently most evidence points towards an important role of elevated prolactin levels or overt hyperprolactinemia with additional triggers such as local trauma or irritation. Alpha 1-antitrypsin deficiency was documented in one case, interferon-alpha therapy in another case. Similar cases of granulomatous mastitis were reported in IgG4-related disease though the exact relationship to IGM remains to be elucidated. Other contributing factors of IGM were investigated such as oral contraceptives usage. Many cases were reported after use of prolactin elevating medications such as antipsychotics.

Elevated prolactin levels have the direct effects of increasing secretory activity of breast lobules, maintaining tight junctions of the ductal epithelium, preventing involution of the breast gland after weaning and are known to stimulate the immune system, contributing to both physiological and pathological granulomatous lesions and non-caseating granulomas. PRL is also secreted locally in the breast and local secretion by lymphocytes may be enhanced during inflammatory reactions.

Autoimmune reaction to extravasated fat and protein rich luminal fluid (denaturized milk) resulting from the secretory activity is assumed to be one of the triggers of IGM. Several other hormones can contribute to PRL signaling in the breast gland, high levels of insulin caused for example by peripheral insulin resistance (resulting from pregnancy, gestational diabetes or developing diabetes mellitus type 2) will enhance the galactogenic and antiapoptotic effects of PRL and growth hormone by acting synergistically with IGF-1.

Symptoms, if any, can be mild even in the presence of significant swelling or masses.

Lacrimal gland involvement may cause swelling of the upper eyelid, or proptosis if there is severe swelling. Other orbital masses or inflammation can result in visual disturbance (blurred vision, double vision, visual field impairment), restricted eye movements, pain or discomfort, numbness in the distribution of the supraorbital and/or infraorbital nerves, or proptosis.

IgG4-related ophthalmic disease has been estimated to account for approximately 25% of all cases of proptosis, eyelid swelling and other features of orbital swelling.

As recognition of IgG4-RD is relatively recent, there are limited studies on its epidemiology. It is therefore difficult to make an accurate estimation of prevalence. Furthermore, age of onset is almost impossible to estimate; age at diagnosis is frequently misused as the age of onset.

A 2011 study estimated the incidence of IgG4-RD in Japan at 2.8–10.8/million population, with a median age of onset of 58 years.

Idiopathic granulomatous mastitis is defined as granulomatous mastits without any other attributable cause such as those above mentioned. It occurs on average two years and almost exclusively up to six years after pregnancy, usual age range is 17 to 42 years. Some cases have been reported that were related to drug induced hyperprolactinemia.

Exceptionally rarely it has been diagnosed during pregnancy and in men.

Riedel's thyroiditis is classified as rare. Most patients remain euthyroid, but approximately 30% of patients become hypothyroid and very few patients are hyperthyroid. It is most seen in women.

Retinal vasculitis is inflammation of the vascular branches of the retinal artery, caused either by primary ocular disease processes, or as a specific presentation of any systemic form of vasculitis such as Behçet's disease, sarcoidosis, multiple sclerosis, or any form of systemic nectrozing vasculitis such as temporal arteritis, polyarteritis nodosa, and granulomatosis with polyangiitis, or due to lupus erythematosus, or rheumatoid arthritis. Eales disease, pars planitis, birdshot retinochoroidopathy (autoimmune bilateral posterior uveitis), and Fuchs heterochromic iridocyclitis (FHI) can also cause retinal vasculitis. Infectious pathogens such as "Mycobacterium tuberculosis", visceral larva migrans ("Toxocara canis" & "Toxocara cati") can also cause retinal vasculitis.

The goal of treatment is the induction and maintenance of remission so as to prevent progression of fibrosis and organ destruction in affected organ(s).

An international panel of experts have developed recommendations for the management of IgG4-RD. They concluded that in all cases of symptomatic, active IgG4-RD that treatment is required. Some cases with asymptomatic IgG4-RD also require treatment, as some organs tend to not cause symptoms until the late stages of disease. Urgent treatment is advised with certain organ manifestations, such as aortitis, retroperitoneal fibrosis, proximal biliary strictures, tubulointerstitial nephritis, pachymeningitis, pancreatic enlargement and pericarditis.

Riedel's thyroiditis, also called Riedel's struma is a chronic form of thyroiditis.

It is now believed that Riedel's thyroiditis is one manifestation of a systemic disease that can affect many organ systems called IgG4-related disease. It is often a multi-organ disease affecting pancreas, liver, kidney, salivary and orbital tissues and retroperitoneum. The hallmarks of the disease are fibrosis and infiltration by IgG4 secreting plasma cells.

Standard, and most effective, therapy to date is glandular sialadenectomy, which is associated with fairly low operative morbidity; however, in recent times, the administration of steroid (which can shrink the inflammatory lesion and is known to reduce serum IgG4 values) has been considered favorably, and may be useful in younger patients or those who refuse surgery.

These are also collectively known as chronic punctate parotitis or chronic autoimmune parotitis.

"Sjögren's syndrome:"

Chronic inflammation of the salivary glands may also be an autoimmune disease known as Sjögren's syndrome. The disease most commonly appears in people aged 40–60 years, but it may affect small children. In Sjögren syndrome, the prevalence of parotitis in women versus men is approximately 9:1. The involved parotid gland is enlarged and tender at times. The cause is unknown. The syndrome is often characterized by excessive dryness in the eyes, mouth, nose, vagina, and skin.

"Lymphoepithelial lesion of Godwin:"

Most frequently associated with a circumscribed tumor with the histologic features of Sjögren syndrome. This designation has also fallen out of favour.

Retinal vasculitis presents as painless, decrease of visual acuity (blurry vision), visual floaters, scotomas (dark spot in vision), decreased ability to distinguish colors, and metamorphopsia (distortion of images such as linear images).

"Acute bacterial parotitis:"

is most often caused by a bacterial infection of Staphylococcus aureus but may be caused by any commensal bacteria.

"Parotitis as Extrapulmonary Tuberculosis:"

The mycobacterium that cause tuberculosis can also cause parotid infection. Those infected tend to have enlarged, nontender, but moderately painful glands. The diagnosis is made by typical chest radiograph findings, cultures, or histologic diagnosis after the gland has been removed. When diagnosed and treated with antitubercular medications, the gland may return to normal in 1–3 months.

"Acute viral parotitis (mumps):"

The most common viral cause of parotitis is mumps. Routine vaccinations have dropped the incidence of mumps to a very low level. Mumps resolves on its own in about ten days.

"HIV parotitis:" Generalized lymphadenopathy has long been associated with HIV, but the localized enlargement of the parotid gland is less well known.

The cause and pathogenesis of this chronic condition are not very well understood. Several factors have been postulated:

- Formation of a hard salivary calculus or sialolith by accumulation of calcium salts in the duct of the salivary gland (a process known as Sialolithiasis). This has been proposed as the most common cause for Küttner's tumor of the submandibular gland, with sialoliths observed in an appreciable proportion of cases. However, sialolith involvement may not be found in many cases.

- Abnormalities of the salivary gland ducts leading to excessive accumulation or retention of ductal secretions, which can excite chronic inflammations.

- Immune, especially autoimmune, cause - which has gained steam, given the observation that the tissue of the glands is overrun with lymphoid immune cells and fibrous connective tissue, as well as corroboration from markedly similar lesions (with histologic and immunohistochemical findings) seen elsewhere in the body. The presence of abundant Immunoglobulin G4 (IgG4) associated with Plasma cells infiltrating into the salivary glands, as well as increased serum IgG4 concentration, has been noted with patients with Küttner's tumor.

This chronic condition is primarily observed in adult (40–70 years) patients. However, Küttner's tumor, with prominent immunopathological features, has been described in an 11-year-old boy in Brazil in 2012.

In 80% of cases, the parotid gland is affected. Lacrimal glands are also affected.

Benign lymphoepithelial lesion is most likely to occur in adults around 50 years of age. There is a predilection for gender with 60–80% being female. The gland affected has a diffuse swelling. The swelling can be asymptomatic, but mild pain can also be associated. There is a preponderance of this disease in those who suffer from HIV infection.

Most cases of benign lymphoepithelial lesions appear in conjunction with Sjögren's syndrome. When Sjögren's syndrome is present, the swelling is usually bilateral. Otherwise, the affected glands are usually only on one side of the body.

In many cases, a biopsy is needed to distinguish benign lymphoepithelial lesions from sialadenosis (sialosis).

Bacterial infections of the orbit have long been associated with a risk of catastrophic local

sequelae and intracranial spread.

The natural course of the disease, as documented by Gamble (1933), in the pre-antibiotic era,

resulted in death in 17% of patients and permanent blindness in 20%.

Some specific reactive lymphadenopathies with a predominantly follicular pattern:

- Rheumatoid arthritis

- Sjogren syndrome

- IgG4-related disease (IgG4-related lymphadenopathy)

- Kimura disease

- Toxoplasmosis

- Syphilis

- Castleman disease

- HIV-associated lymphadenopathy

- Progressive transformation of germinal centers (PTGC)

The varicella-zoster virus antigen was found in 74% of temporal artery biopsies that were GCA-positive, suggesting that the VZV infection may trigger the inflammatory cascade.

The disorder may coexist (in a half of cases) with polymyalgia rheumatica (PMR), which is characterized by sudden onset of pain and stiffness in muscles (pelvis, shoulder) of the body and is seen in the elderly. GCA and PMR are so closely linked that they are often considered to be different manifestations of the same disease process. Other diseases associated with temporal arteritis are systemic lupus erythematosus, rheumatoid arthritis, and severe infections.

Giant-cell arteritis can involve branches of the aorta as well, leading to an aortic aneurysm or dissection. For this reason, patients should be followed with serial chest X-rays.

The epidemiology of Idiopathic sclerosing mesenteritis disease is extremely rare and has only been diagnosed in about an estimated 300 patients worldwide to date (as of 2014), it is probably under diagnosed.

It can occur in children.

Giant-cell arteritis (GCA), also called temporal arteritis, is an inflammatory disease of blood vessels. Symptoms may include headache, pain over the temples, flu-like symptoms, double vision, and difficulty opening the mouth. Complication can include blockage of the artery to the eye with resulting blindness, aortic dissection, and aortic aneurysm. GCA is frequently associated with polymyalgia rheumatica.

The cause is unknown. The underlying mechanism involves inflammation of the small blood vessels that occur within the walls of larger arteries. This mainly affects arteries around the head and neck, though some in the chest may also be affected. Diagnosis is suspected based on symptoms, blood tests, and medical imaging, and confirmed by biopsy of the temporal artery. However, in about 10% of people the temporal artery is normal.

Treatment is typically with high doses of steroids, such as prednisone. Once symptoms have resolved the dose is then decreased by about 15% per month. Once a low dose is reached, the taper is slowed further over the subsequent year. Other medications that may be recommended include bisphosphonates to prevent bone loss and a proton pump inhibitor to prevent stomach problems.

It affects about 1 in 15,000 people over the age of 50 a year. The condition typically only occurs in those over the age of 50 being most common among those in their 70s. Females are more often affected than males. Those of northern European descent are more commonly affected. Life expectancy is typically normal. The first description of the condition occurred in 1890.

Multifocal fibrosclerosis and idiopathic fibrosclerosis are disorders of unknown aetiology, characterised by fibrous lesions (co-)occurring at a variety of sites. Known manifestations include retroperitoneal fibrosis, mediastinal fibrosis and Riedel's thyroiditis.

They are now considered to be manifestations of IgG4-related disease.

IgG4-related disease responds well, and often dramatically, to glucocorticoid therapy, provided that advanced fibrotic lesions have not resulted in irreversible damage, and this has included resolution of radiologic findings. Men given glucocorticoids to treat IgG4-related disease at other anatomical sites sometimes report relief of their lower urinary tract symptoms, suggesting that IgG4-related prostatitis may be underdiagnosed.

Cases are however likely to get misdiagnosed as benign prostatic hyperplasia and to get treated alternatively with medications such as alpha blockers. The efficacy of alpha blockers in IgG4-related prostatitis remains unclear.