The key symptoms of PFAPA are those in its name: periodic high fever at intervals of about 3–5 weeks, as well as aphthous ulcers, pharyngitis and/or adenitis. In between episodes, and even during the episodes, the children appear healthy. At least 6 months of episodes. Diagnosis requires recurrent negative throat cultures and that other causes (such as EBV, CMV, FMF) be excluded.

Periodic fever, aphthous stomatitis, pharyngitis and adenitis or periodic fever aphthous pharyngitis and cervical adenopathy (PFAPA) syndrome is a medical condition, typically starting in young children, in which high fever occurs periodically at intervals of about 3–5 weeks, frequently accompanied by aphthous-like ulcers, pharyngitis and/or cervical adenitis (cervical lymphadenopathy). The syndrome was described in 1987 and named two years later.

There are seven types of attacks. Ninety percent of all patients have their first attack before they are 18 years old. All develop over 2–4 hours and last anywhere from 6 hours to 4 days. Most attacks involve fever.

1. Abdominal attacks, featuring abdominal pain, affect the whole abdomen with all signs of peritonitis (inflammation of abdominal lining), and acute abdominal pain like appendicitis. They occur in 95% of all patients and may lead to unnecessary laparotomy. Incomplete attacks, with local tenderness and normal blood tests, have been reported.

2. Joint attacks mainly occur in large joints, especially in the legs. Usually, only one joint is affected. 75% of all FMF patients experience joint attacks.

3. Chest attacks include pleuritis (inflammation of the pleura) and pericarditis (inflammation of the pericardium). Pleuritis occurs in 40% of patients and makes it difficult to breathe or lie flat, but pericarditis is rare.

4. Scrotal attacks due to inflammation of the tunica vaginalis occurs in up to 5% and may be mistaken for acute scrotum (i.e. testicular torsion).

5. Myalgia (rare in isolation)

6. Erysipeloid (a skin reaction on the legs, rare in isolation)

7. Fever without any of the other symptoms listed above (25%)

AA-amyloidosis with kidney failure is a complication and may develop without overt crises. AA amyloid protein is produced in very large quantities during attacks, and at a low rate between them, and accumulates mainly in the kidney, as well as the heart, spleen, gastrointestinal tract, and thyroid.

There appears to be an increase in the risk for developing particular vasculitis-related diseases (e.g. Henoch–Schönlein purpura), spondylarthropathy, prolonged arthritis of certain joints and protracted myalgia.

Based on severity, authors have classified VKC into clinical grades:

Grade 0 - Absence of symptoms

Grade 1 MILD - Symptoms but no corneal involvement

Grade 2 MODERATE - Symptoms with photophobia but no corneal involvement

Grade 3 SEVERE - Symptoms, photophobia, milfd to moderate SPK's OR with Diffuse SPK or corneal ulcer

Corneal involvement in VKC may be primary or secondary due to extension of limbal lesions. Vernal keratopathy includes 5 types of lesions.

1. Punctuate epithelial keratitis.

2. Ulcerative vernal keratitis.

3. Vernal corneal plaques.

4. Subepithelial scarring.

5. Pseudogerontoxon.

TNF receptor associated periodic syndrome presents with the following signs and symptoms:

- Episodic fever

- Erythrocyte sedimentation rate(increased)

- Pericarditis

- Splenomegaly

- Uveitis

- Vertigo

The syndromes within CAPS overlap clinically, and patients may have features of more than one disorder. In a retrospective cohort of 136 CAPS patients from 16 countries, the most prevalent clinical features were fever (84% of cases, often with concurrent constitutional symptoms such as fatigue, malaise, mood disorders or failure to thrive), skin rash (either urticarial or maculopapular rash; 97% of cases) especially after cold exposure, and musculoskeletal involvement (myalgia, arthralgia, and/or arthritis, or less commonly joint contracture, patellar overgrowth, bone deformity, bone erosion and/or osteolytic lesion; 86% of cases). Less common features included ophthalmological involvement (conjunctivitis and/or uveitis, or less commonly optic nerve atrophy, cataract, glaucoma or impaired vision; 71% of cases), neurosensory hearing loss (42% of cases), neurological involvement (morning headache, papilloedema, and/or meningitis, or less commonly seizure, hydrocephalus or mental retardation; 40% of cases), and AA amyloidosis (4% of cases). Age of onset is typically in infancy or early childhood. In 57% of cases, CAPS had a chronic phenotype with symptoms present almost daily, whereas the remaining 43% of patients experienced only acute episodes. Up to 56% of patients reported a family history of CAPS. Previous studies confirm these symptoms, although the exact reported rates vary.

Repeated, periodic joint effusions of the knee. Usually one knee is affected but sometimes both knees. Other joints may also be involved along with the knee. Effusions are large, restricting range of motion but significant pain is not a feature. There is usually stiffness. Tenderness of the joint may or may not be present. Aspirated synovial fluid is usually sterile but will sometimes show elevated cell count (>100 cells/mL) with 50% being polymorphonuclear leukocytes.

Onset of effusions are sudden with no particular trigger or stimulus. Each episode lasts for a few days to about a week and recurs in cycles of 7 to 11 days with extremes of 3 days to 30 days also reported. Sometimes the joint may begin to swell again as soon as the fluid has subsided. Where both knees are affected concurrently, as one joint ceases to swell the other may become involved.

The cycle of joints swellings have been reported as being very regular, even predictable. This has been a characteristic feature of IH in many case reports. However, over the longer-term especially, these cycles of effusion and recovery may not be as constant as first reported.

In women, many cases seem to begin at puberty. Episodes of knee swelling may coincide the menstrual cycle. In nearly all case reports, pregnancy seems to suppress the condition but after birth, during lactation, it returns.

In the main, patients are mostly free of other symptoms. Fever is rare. There no signs of local inflammation or lymphatic involvement. Laboratory tests are generally normal or within reference limits.

Cryopyrin-associated periodic syndrome (CAPS) is a group of rare, heterogeneous autoinflammatory disease characterized by interleukin 1β-mediated systemic inflammation and clinical symptoms involving skin, joints, central nervous system, and eyes. It encompasses a spectrum of three clinically overlapping autoinflammatory syndromes including familial cold autoinflammatory syndrome (FCAS, formerly termed familial cold-induced urticaria), the Muckle–Wells syndrome (MWS), and neonatal-onset multisystem inflammatory disease (NOMID, also called chronic infantile neurologic cutaneous and articular syndrome or CINCA) that were originally thought to be distinct entities, but in fact share a single genetic mutation and pathogenic pathway.

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.

The age of onset is almost always before 3 months of age. Many infants are born preterm (1/3 cases) and dysmature. The babies are frequently small for dates. The placenta may be abnormal with non-specific inflammation on histology. Umbilical cord anomalies have occasionally been reported. In severe cases, signs in the brain may be detected on prenatal ultrasound.

The presentation is pleiomorphic, making the diagnosis difficult, but the most common features of this disease involve the skin, joints, and central nervous system.

All have a maculopapular urticarial skin rash that is often present at birth (75% cases). It is probably more correctly described as an urticarial-like rash. The presence of the rash varies with time, and biopsy of these skin lesions shows a perivascular inflammatory infiltrate including granulocytes.

In about 35-65% of cases, arthritis occurs. Joint signs are variably expressed and can lead to transient swelling without sequelae between crises, or to unpredictable anomalies of growth cartilage and long bones epiphyses suggestive of a pseudo-tumour. Biopsies reveal hypertrophic cartilage without inflammatory cells. This most commonly affects the large joints (knees, ankles, elbows, and wrists) but may also involve the small joints of the hands and feet. It is usually bilateral and painful. A common and characteristic feature is giant kneecaps. Severe cases may result in contractures (joint deformities).

Most patients eventually have neurological problems. These manifest themselves in three principal ways: chronic meningitis, involvement of both the optic tract and eye, and sensorineural hearing loss. The chronic meningitis presents with the features of chronically raised intracranial pressure: headaches, vomiting, ventriculomegaly, hydrocephalus, macromegaly, cerebral atrophy, and optic atrophy. Some of these features may be evidenced on prenatal ultrasound. In 50% of cases, intellectual deficit occurs. Seizures occur in 25% of cases, but other manifestations are rare. Histological examination shows infiltration of the meninges with polymorphs.

Ocular manifestations occur in 80% of cases and include uveitis (70%), papillary involvement, conjunctivitis, and optical neuritis. If untreated, these may result in blindness (25%). The sensorineural hearing loss occurs in 75%, and tends to be progressive leading to deafness in 20% of cases.

Almost all children are remarkably short and have growth delay. Fever is extremely common but inconstant and is most often mild. Anemia is frequent. Other findings that have been reported include macrocephaly (95%), large fontanelle, prominent forehead, flattening of the nasal bridge (saddleback nose), short and thick extremities, and finger clubbing. The liver and/or spleen may be enlarged. Lymph node enlargement may also be present.

Later in life, secondary amyloidosis may occur. Delayed puberty and secondary amenorrhoea are not uncommon. Hoarseness due to inflammation of the laryngeal cartilage has also been reported.

TNF receptor associated periodic syndrome (also known as TRAPS,) is a periodic fever syndrome associated with mutations in a receptor for the molecule tumor necrosis factor (TNF) that is inheritable in an autosomal dominant manner. Individuals with TRAPS have episodic symptoms such as recurrent high fevers, rash, abdominal pain, joint/muscle aches and puffy eyes.

HIDS is one of a number of periodic fever syndromes. It is characterised by attacks of fever, arthralgia, skin lesions including cyclical mouth ulcers, and diarrhea. Laboratory features include an acute phase response (elevated CRP and ESR) and markedly elevated IgD (and often IgA), although cases with normal IgD have been described.

It has mainly been described in the Netherlands and France, although the international registry includes a number of cases from other countries.

The differential diagnosis includes fever of unknown origin, familial Mediterranean fever (FMF) and familial Hibernian fever (or TNFα reception associated periodic syndrome/TRAPS).

Intermittent hydrarthrosis (IH), also known as "periodic synoviosis", "periodic benign synovitis", or "periodic hydrarthritis", is a chronic condition of unknown cause characterized by recurring, temporary episodes of fluid accumulation in the knee. While the knee is mainly involved, occasionally other joints such as the elbow or ankle can additionally be affected. Fluid accumulation in the joint can be extensive causing discomfort and impairing movement, although affected joints are not usually very painful. While the condition is chronic, it does not appear to progress to more destructive damage of the joint. It seems to affect slightly more women than men.

Episodes of swelling last several days or longer, can occur with regular or semi-regular frequency, typically one or two episodes per month. Between periods of effusion, knee swelling reduces dramatically providing largely symptomless intervals. Unlike some other rheumatological conditions such as rheumatoid arthritis, laboratory findings are usually within normal ranges or limits.

Clear treatment options have yet to be established. NSAIDs and COX2-inhibitors are generally not effective. Where this condition has been correctly diagnosed, various anti-rheumatic drugs as well as colchicine may be trialled to find the most effective option. More aggressive intra-articular treatment such chemical or radio-active synovectomy can also be helpful although benefits beyond 1 year have not been reported in literature.

Muckle–Wells syndrome (MWS), also known as urticaria-deafness-amyloidosis syndrome (UDA), is a rare autosomal dominant disease which causes sensorineural deafness and recurrent hives, and can lead to amyloidosis. Individuals with MWS often have episodic fever, chills, and joint pain. As a result, MWS is considered a type of periodic fever syndrome. MWS is caused by a defect in the CIAS1 gene which creates the protein cryopyrin. MWS is closely related to two other syndromes, familial cold urticaria and neonatal onset multisystem inflammatory disease—in fact, all three are related to mutations in the same gene and subsumed under the term cryopyrin-associated periodic syndromes (CAPS).

CRMO/CNO is a diagnosis of exclusion. This means that other diseases must be ruled out before the diagnosis can be made. Generally, many tests are required, such as blood tests, x-rays, bone scans, MRI and often a bone biopsy.

Chronic recurrent multifocal osteomyelitis (CRMO) ("multifocal" because it can erupt in different sites, primarily bones; "osteomyelitis" because it is very similar to that disease but appears to be without any infection), also known as chronic recurring multifocal osteomyelitis, is a rare condition (1:1,000,000), in which the bones have lesions, inflammation, and pain. Its definition is evolving. Many doctors and articles described CRMO as an autoimmune disease that has symptoms similar to osteomyelitis, but without the infection. Some doctors thought CRMO was related to SAPHO syndrome. Research now classifies CRMO as an inherited autoinflammatory disease but have yet to isolate the exact gene responsible for it. Some specialists believe they have discovered a link between CRMO with a rare allele of marker D18S60, resulting in a haplotype relative risk (HRR) of 18. Other experts found that "mutations in LPIN2 cause a syndromic form of chronic recurrent multifocal osteomyelitis known as Majeed syndrome, while mutations in pstpip2 cause a murine form of the disorder. The roles played by LPIN2 and the human homolog of pstpip2, PSTPIP2, in the cause of chronic recurrent multifocal osteomyelitis are uncertain. The professional theories seem to be moving in the direction of an inherited gene.

Neonatal-onset multisystem inflammatory disease (abbreviated NOMID, also known as chronic infantile neurologic cutaneous and articular syndrome, or CINCA) is a rare genetic periodic fever syndrome which causes uncontrolled inflammation in multiple parts of the body starting in the newborn period. Symptoms include skin rashes, severe arthritis, and chronic meningitis leading to neurologic damage. It is one of the cryopyrin-associated periodic syndromes.

NOMID can result from a mutation in the "CIAS1" gene (also known as "NLRP3" gene), which helps control inflammation. Mutations in this gene also cause familial cold urticaria and Muckle–Wells syndrome. NOMID has been successfully treated with the drug anakinra.

This syndrome is also known as the Prieur–Griscelli syndrome as it was first described by these authors in 1981.

The primary symptoms of a cytokine storm are high fever, swelling, redness, extreme fatigue, and nausea. In some cases the immune reaction will be fatal.

Schnitzler syndrome is a rare disease characterised by chronic hives (urticaria) and periodic fever, bone pain and joint pain (sometimes with joint inflammation), weight loss, malaise, fatigue, swollen lymph glands and enlarged spleen and liver.

The urticarial rash is non-itching in more than half of cases, which is unusual for hives. It is most prominent on the trunk, arms and legs, sparing the palms, soles, head and neck. Associated angioedema has been reported in a few patients. A review of 94 cases found a mean age at onset of 51 years, and only four patients developed symptoms before the age of 35. The cause and disease mechanism of Schnitzler syndrome remain largely unknown.

Schnitzler syndrome is considered an autoinflammatory and autoimmune disorder. Chronic hives and a monoclonal gammopathy have been proposed as the major criteria, while the others represent minor criteria.

Blood tests show a high concentration of specific gamma-globulins (monoclonal gammopathy) of the IgM type. It almost always has light chains of the κ-type. A variant in which IgG is raised has been described, which appears to be ten times as rare. The immunoglobulins may show up in the urine as Bence Jones proteins. Signs of inflammation are often present: these include an increased white blood cell count (leukocytosis) and a raised erythrocyte sedimentation rate and C-reactive protein. There can be anemia of chronic disease. Bone abnormalities can be seen on radiological imaging (often increased density or osteosclerosis) or biopsy.

Because it is such a rare condition (as of September 2014, only 281 cases have been reported), it is important to rule out other conditions which can cause periodic fevers, paraproteins or chronic hives. These include (and are not limited to) autoimmune or autoinflammatory disorders such as adult-onset Still's disease, angioedema, hematological disorders such as lymphoma or monoclonal gammopathy of undetermined significance, other causes of hives, cryoglobulinemia, mastocytosis, chronic neonatal onset multisystem inflammatory disease or Muckle–Wells syndrome.

It is however possible to have more than one rare condition as seen by a patient with Schnitzler's syndrome and cold induced urticaria.

A meeting of experts, including Dr Liliane Schnitzler (then retired) took place in Strasbourg in May 2012 and drew up diagnostic criteria known as the "Strasbourg Criteria". These included two obligate criteria (chronic urticarial rash and monoclonal IgM or IgG) and several minor criteria; a definite diagnosis requires the two obligate criteria and two minor criteria if IgM, three if IgG; a probable diagnosis requires the two obligate criteria and one (IgM) or two (IgG) minor criteria.

The chronic inflammation present in MWS over time can lead to deafness. In addition, the prolonged inflammation can lead to deposition of proteins in the kidney, a condition known as amyloidosis.

Hyperimmunoglobulinemia D with recurrent fever (HIDS) is a periodic fever syndrome originally described in 1984 by the internist Jos van der Meer, then at Leiden University Medical Centre. No more than 300 cases have been described worldwide.

A cytokine storm, also known as cytokine cascade and hypercytokinemia, is a potentially fatal immune reaction consisting of a positive feedback loop between cytokines and white blood cells, with highly elevated levels of various cytokines. The term arose in the field of pathophysiology in discussions around immune disorders in 1993, was extended to discussions of infectious disease and sepsis, and has been used to describe severe manifestations of cytokine release syndrome, an adverse effect of some drugs.