Nodular regenerative hyperplasia is a form of liver hyperplasia associated with portal hypertension.

Nodular regenerative hyperplasia (NRH) is a rare liver condition characterized by a widespread benign transformation of the hepatic parenchyma into small regenerative nodules. NRH may lead to the development of non-cirrhotic portal hypertension. There are no published systematic population studies on NRH and our current knowledge is limited to case reports and case series. NRH may develop "via" autoimmune, hematological, infectious, neoplastic, or drug-related causes. It is associated with rheumatoid arthritis, Felty syndrome, myeloproliferative disorders, liver, kidney and bone marrow transplantation, cytotoxic drugs like azathioprine, mercaptopurine, thioguanine, antiretroviral drugs for HIV like didanosine and vitamin A. The disease is usually asymptomatic, slowly or non-progressive unless complications of portal hypertension develop. Accurate diagnosis is made by histopathology, which demonstrates diffuse micronodular transformation without fibrous septa. Lack of perinuclear collagen tissue distinguishes NRH from typical regenerative nodules in the cirrhotic liver. While the initial treatment is to address the underlying disease, ultimately the therapy is directed to the management of portal hypertension. The prognosis of NRH depends on both the severity of the underlying illness and the prevention of secondary complications of portal hypertension. In this review we detail the epidemiology, pathogenesis, diagnosis, management, and prognosis of NRH.

It can be a complication of azathioprine therapy.

PAM is one of the rare lung diseases currently being studied by the Rare Lung Diseases Consortium (RLDC). Pulmonary Alveolar Microlithiasis patients, families, and caregivers are encouraged to join the NIH Rare Lung Diseases Consortium Contact Registry. This is a privacy protected site that provides up-to-date information for individuals interested in the latest scientific news, trials, and treatments related to rare lung diseases.

Since the disease was first described in 1918, over 500 case reports have appeared in the literature. PAM is associated with consanguinity. The incidence is higher in Turkey, Japan, India and Italy. The mean age at diagnosis is 35 years based on the cases reported in the literature.

Progressive nodular histiocytoma is a cutaneous condition characterized by generalized, discrete yellow papules and nodules with prominent facial involvement.

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.

As the number of published cases of AIP has increased, efforts have been focused on defining AIP as a distinct clinical and pathologic entity and toward developing some generally agreed upon diagnostic criteria and nomenclature. Terms frequently encountered are autoimmune or autoimmune-related pancreatitis, lymphoplasmacytic sclerosing pancreatitis, idiopathic tumefactive chronic pancreatitis, idiopathic pancreatitis with focal irregular narrowing of the main pancreatic duct, and non-alcoholic duct destructive chronic pancreatitis. There are also a large number of case reports employing descriptive terminology such as pancreatitis associated with Sjögren’s syndrome, primary sclerosing cholangitis, or inflammatory bowel disease. Some of the earliest cases were reported as pancreatic pseudotumor or pseudolymphoma.

Nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD) is a rare and serious syndrome that involves fibrosis of skin, joints, eyes, and internal organs. The first cases were identified in 1997 and its cause is not fully understood. However, evidence suggests NSF is associated with exposure to gadolinium (with gadolinium-based MRI contrast agents being frequently used as contrast agents for magnetic resonance imaging (MRI)) in patients with severe kidney failure. Epidemiological studies suggest that the incidence of NSF is unrelated to gender, ethnicity, or age and it is not thought to have a genetic basis. A registry for NSF has identified about 335 cases as of 2011.

Most patients with NSF have undergone hemodialysis for kidney failure, some have never undergone dialysis and others have received only peritoneal dialysis. Many people with NSF have taken immunosuppressive medications and have other diseases, such as hepatitis C. Four of the seven gadolinium contrast agents approved by the U.S. Food and Drug Administration have been principally implicated in NSF, including gadodiamide, gadopentetate, and gadoversetamide. Gadobenate has also been associated with NSF, but further research has shown that gadobenate diglumine might be safe even in patients undergoing dialysis.

Mortality is indirect and caused by complications. After cholangitis occurs, patients typically die within 5–10 years.

The first cases of NSF were identified in 1997, but NSF was first described as an independent disease entity in 2000. While skin involvement is on the foreground, the process may involve any organ and resembles diffuse scleroderma or systemic sclerosis. In 2006, the link between NSF and gadolinium-containing contrast agents was made. As a result, gadolinium-containing contrast is now considered contraindicated in patients with an estimated glomerular filtration rate (a measure of renal function) under 60 and especially under 30 ml/mn. One retrospective study of the Veterans Affairs Electronic Medical Record found no cases of NSF among 141 patients receiving hemodialysis for chronic kidney disease who received gadoteridol.

FNH is not a true neoplasm; it is believed to result from localized hyperplastic hepatocyte response to an underlying congenital arteriovenous malformation. It consists of normal liver constituents in an abnormally organized pattern, grows in a stellate pattern and may display central necrosis when large. Additionally evidence suggests that the incidence of FNH is related to oral contraceptive use.

Focal nodular hyperplasia (FNH) is a benign tumor of the liver (hepatic tumor), which is the second most prevalent tumor of the liver (the first is hepatic hemangioma). It is usually asymptomatic, rarely grows or bleeds, and has no malignant potential. This tumour was once often resected because it was difficult to distinguish from hepatic adenoma, but with modern multiphase imaging is usually now diagnosed by strict imaging criteria and not resected.

Until recently, nodular fasciitis have been considered a reactive process of uncertain cause. However, recent findings indicate that nodular fasciitis is a self-limited clonal neoplastic process (see below). Clinically, nodular fasciitis presents as a subcutaneous "growth" over a period of 3–6 weeks that eventually regresses. The lesion usually reaches a size of 2–3 cm. Larger lesions are unusual. Local recurrence has been described after simple surgical excision but it is rare.

Nodular fasciitis, also known as nodular pseudosarcomatous fasciitis, pseudosarcomatous fasciitis, and subcutaneous pseudosarcomatous fibromatosis, is a benign soft tissue lesion most commonly found in the superficial fascia. The lesion commonly occurs in the first three decades of life. Upper extremities and trunk are the most common affected anatomical sites. Previous history of trauma may be present. Clinically and histologically, nodular fasciitis may be mistaken for a sarcoma.

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.

Many conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Nourishment is provided to these layers by diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface. In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis. The superficial papillary dermis with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone. Structural components of the dermis are collagen, elastic fibers, and ground substance. Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands. The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels. The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia. This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus. The main cellular component of this tissue is the adipocyte, or fat cell. The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance. Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on. Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). Diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data.

ILD may be classified according to the cause. One method of classification is as follows:

1. Inhaled substances

- Inorganic

- Silicosis

- Asbestosis

- Berylliosis

- printing workers (eg. carbon bblack, ink mist)

- Organic

- Hypersensitivity pneumonitis

2. Drug-induced

- Antibiotics

- Chemotherapeutic drugs

- Antiarrhythmic agents

3. Connective tissue and Autoimmune diseases

- Rheumatoid arthritis

- Systemic lupus erythematosus

- Systemic sclerosis

- Polymyositis

- Dermatomyositis

4. Infection

- Atypical pneumonia

- Pneumocystis pneumonia (PCP)

- Tuberculosis

- "Chlamydia" trachomatis

- Respiratory Syncytial Virus

5. Idiopathic

- Sarcoidosis

- Idiopathic pulmonary fibrosis

- Hamman-Rich syndrome

- Antisynthetase syndrome

6. Malignancy

- Lymphangitic carcinomatosis

7. Predominantly in children

- Diffuse developmental disorders

- Growth abnormalities deficient alveolarisation

- Infant conditions of undefined cause

- ILD related to alveolar surfactant region

The presence of rheumatoid arthritis alters how a person's immune system responds to foreign materials, such as dust from a coal mine. When a person with rheumatoid arthritis is exposed to such offensive materials, they are at an increased risk of developing pneumoconiosis.

Caroli disease is typically found in Asia, and diagnosed in persons under the age of 22. Cases have also been found in infants and adults. As medical imaging technology improves, diagnostic age decreases.

Equine multinodular pulmonary fibrosis is a chronic lung disease of horses. There is evidence that the disease is caused by infection with a gammaherpesvirus, equine herpesvirus 5. The disease affects adult (usually older) horses, causing weight loss and reduced ability to exercise as a result of the formation of nodular lesions in the lungs.

Caplan syndrome occurs only in patients with both RA and pneumoconiosis related to mining dust (coal, asbestos, silica). The condition occurs in miners (especially those working in anthracite coal-mines), asbestosis, silicosis and other pneumoconioses. There is probably also a genetic predisposition, and smoking is thought to be an aggravating factor.

Superficial spreading melanoma (also known as "superficially spreading melanoma") (SSM) is usually characterized as the most common form of cutaneous melanoma in Caucasians. The average age at diagnosis is in the fifth decade, and it tends to occur on sun-exposed skin, especially on the backs of males and lower limbs of females.

Benign nephrosclerosis refers to the renal changes most commonly occurring in association with long-standing hypertension. It is termed benign because it rarely progresses to clinically significant renal insufficiency or renal failure.

IgG4-related disease (IgG4-RD), formerly known as IgG4-related systemic disease, is a chronic inflammatory condition characterized by tissue infiltration with lymphocytes and IgG4-secreting plasma cells, various degrees of fibrosis (scarring) and a usually prompt response to oral steroids. In approximately 51–70% of people with this disease, "serum" IgG4 concentrations are elevated during an acute phase.

It is a relapsing–remitting disease associated with a tendency to mass forming, tissue-destructive lesions in multiple sites, with a characteristic histopathological appearance in whichever site is involved. Inflammation and the deposition of connective tissue in affected anatomical sites can lead to organ dysfunction, or even organ failure, if not treated.

Early detection is important to avoid organ damage and potentially serious complications. Treatment is recommended in all symptomatic cases of IgG4-RD and also in asymptomatic IgG4-RD involving certain anatomical sites.

Interstitial lung disease (ILD), or diffuse parenchymal lung disease (DPLD), is a group of lung diseases affecting the interstitium (the tissue and space around the air sacs of the lungs). It concerns alveolar epithelium, pulmonary capillary endothelium, basement membrane, perivascular and perilymphatic tissues. It may occur when an injury to the lungs triggers an abnormal healing response. Ordinarily, the body generates just the right amount of tissue to repair damage. But in interstitial lung disease, the repair process goes awry and the tissue around the air sacs (alveoli) becomes scarred and thickened. This makes it more difficult for oxygen to pass into the bloodstream. The term ILD is used to distinguish these diseases from obstructive airways diseases.

In children, several unique forms of ILD exist which are specific for the young age groups. The acronym chILD is used for this group of diseases and is derived from the English name, Children’s Interstitial Lung Diseases – chILD.

Prolonged ILD may result in pulmonary fibrosis, but this is not always the case. Idiopathic pulmonary fibrosis is interstitial lung disease for which no obvious cause can be identified (idiopathic), and is associated with typical findings both radiographic (basal and pleural based fibrosis with honeycombing) and pathologic (temporally and spatially heterogeneous fibrosis, histopathologic honeycombing and fibroblastic foci).

In 2013 interstitial lung disease affected 595,000 people globally. This resulted in 471,000 deaths.

The cause of prurigo nodularis is unknown, although other conditions may induce PN. PN has been linked to Becker's nevus, linear IgA disease, an autoimmune condition, liver disease and T cells. Systemic pruritus has been linked to cholestasis, thyroid disease, polycythaemia rubra vera, uraemia, Hodgkins disease, HIV and other immunodeficiency diseases. Internal malignancies, liver failure, renal failure, and psychiatric illnesses have been considered to induce PN, although more recent research has refuted a psychiatric cause for PN. Patients report an ongoing battle to distinguish themselves from those with psychiatric disorders such as delusions of parasitosis and other psychiatric conditions.