Evaluation of recurrent fevers (PFAPA/SURF and others)

1. Introduction

Fever is one of the most common symptoms in pediatrics and is estimated to account for approximately one-third of all pediatric visits in primary healthcare. In children, elevated body temperature is defined as follows: rectal temperature above 37.9°C, axillary temperature above 37°C, oral temperature above 37.5°C, and ear temperature above 37.9°C for children under 11 years of age and above 37.5°C for children older than 11 years. Within pediatric practice, fever can be categorized into several types.

A distinct category of febrile conditions includes periodic or recurrent fever syndromes, classified as autoinflammatory diseases. These disorders are characterized by excessive inflammation mediated by the innate immune system, often with a genetic predisposition. To meet the diagnostic criteria, at least three episodes of unexplained fever must occur at intervals greater than seven days over a six-month period. Fever episodes are often high (≥39°C), and their intervals can be regular or irregular. Between episodes, the child is typically well and exhibits normal growth. During febrile episodes, laboratory findings show leukocytosis and elevated acute-phase inflammatory markers, which normalize when the fever subsides. These syndromes typically begin within the first 10 years of life, with a positive family history in many cases. Ethnic background can also play a role in predisposition. 

2. Pathogenesis

Autoinflammatory diseases are clinical disorders characterized by recurrent or persistent inflammation (increased acute phase reactants) and a deficient primary pathogenic role of adaptive immunity (autoreactive T-lymphocytes or autoantibodies), resulting from a lack of regulation or dysregulation of innate immunity. Those diseases manifest with recurrent episodes of systemic inflammation due to intense non-specific inflammatory activation without a known or sufficient cause. Pathogenically speaking, the innate immune system is non-specifically or inadequately activated. Disease flares can occur due to trauma, immunization, infection, stress, etc., or without any apparent triggers.

Autoinflammatory diseases can be divided into monogenic (i.e., resulting from a mutation in one well-defined gene) and polygenic. Conditions falling into the latter group are those with clinical and biological features of autoinflammatory diseases and no known causative gene or genes (for example, PFAPA syndrome, Schnitzler syndrome, systemic juvenile idiopathic arthritis) as well as some multifactorial disorders which are polygenic, i.e., defined by complex interactions of multiple genetic and environmental factors, showing no features of Mendelian inheritance pattern (e.g., gout, Behçet disease).

The majority of known monogenic autoinflammatory diseases are in fact inflammasomopathies since they result from mutations in inflammasome component genes. Inflammasomopathies result from mutations of genes associated with components of inflammasomes, intracellular multiprotein complexes that form in granulocyte and macrophage cytoplasm as a response to so-called danger signals. Danger signals are in fact various extracellular molecules derived from microorganisms or damaged cells. By binding to respective receptors they trigger an inflammatory cascade consisting of two steps: the first step, “signal 1”, mediated by nuclear factor kappa B (NF-kB), and the second step, “signal 2”, which leads to inflammasome formation. “Signal 1” triggers the transcription of inflammasome components, pro-interleukin 18 and pro-interleukin 1 beta (pro-IL-1β), a precursor of interleukin 1β (IL-1β). “Signal 2”, as mentioned, results in inflammasome formation leading to caspase-1 activation that transforms pro-IL-1β into IL-1β and pro-IL-18 into IL-18. Interleukins 1β and 18 are active forms which leave the cell and incite inflammation (Figure 1).

Figure 1 Pathogenesis of inflammasomopathies. Step 1 – binding of danger signals to respective receptors. Step 2 – transcription of inflammasome components, pro-interleukin 18 and pro-interleukin 1 beta. Step 3 – inflammasome formation. Step 4 – caspase-1 activation and transforming pro-IL-1β into IL-1β and pro-IL-18 into IL-18.

Legend: ASC – apoptosis-associated speck-like protein containing a CARD (caspase recruiting domain); Cox-2 – cyclooxygenase-2; DAMP – damage associated molecular pattern; IL– interleukin; IL-1Ra – interleukin-1 receptor antagonist; NK – natural killer; NOD – nucleotide-binding oligomerization domain-like receptors; NF-κB – nuclear factor kappa-light-chain-enhancer of activated B cell; PAMP – pathogen-associated molecular pattern; Phl – phospholipase; PGE2 – prostaglandin E2; PRR – pattern recognition receptor; PSTPIP1 – proline-serine-threonine phosphatase interacting protein 1; TNF – tumour necrosis factor.

Various genes for various inflammasomes are mutated in various inflammasomapathies: NRLP3 (cryopirine-associated periodic fever syndromes), NRLC4 (macrophage activation syndrome, syndrome of enterocolitis and self-inflammation), NLRP12 (FCAS2, i.e., familial cold inflammatory syndrome 2). The mentioned mutations lead to an overproduction of proinflammatory cytokines, primarily IL-1 but also IL6, IL-18, and TNF-α (tumor necrosis factor α). Familial Mediterranean fever is a consequence of the pyrin gene mutation. Mevalonate kinase defficiency (formerly known as hyper-IgD syndrome) also results from an overstimulation of pyrin and overproduction of IL-1. Mutations of the TNFRSF1A gene also lead to inflammasome overactivation. Most common clinical findings in inflammasomopathies are fever (mostly periodic), rash, serositis, hepatosplenomegaly, and lymphadenopathy. The basis of management in the majority of these disorders are IL-1 inhibitors.

3. Clinical manifestations

Members of this group of disorders are monogenic periodic fever syndromes (i.e., familial Mediterranean fever, mevalonate kinase deficiency, TNF-receptor-associated periodic fever, cyropirine-associated periodic fever syndromes), which were in fact the first described examples of autoinflammatory diseases. 

Based on episode duration, periodic fever syndromes can be categorized as follows:

• Short episodes (24–48 hours): Familial Mediterranean fever (FMF)
• Medium-length episodes (4–7 days): Mevalonate kinase deficiency (MKD)
• Prolonged episodes: TNF receptor-associated periodic syndrome (TRAPS)

In March 2017, at a Consensus Conference held in Genoa, an expert group consisting of clinicians and geneticists established a new set of classification and clinical criteria for inherited periodic fever syndromes and PFAPA syndrome. The new criteria, known as the Eurofever/PRINTO (Pediatric Rheumatology International Trials Organization) criteria, are used in clinical and epidemiological research and are shown in Tables 1 and 2. According to the criteria, each disease needs a confirmed gene mutation. If a gene mutation is pathogenic or its pathogenicity is highly probable, fewer clinical parameters need to be fulfilled for the diagnosis; the opposite is the case if the mutation is not proven to be pathogenic or is unlikely pathogenic. The aforementioned expert group also established clinical criteria that are not based on gene testing and can be used in everyday clinical practice. Since cryopyrin-associated periodic syndromes (CAPS) manifest in a broad clinical spectrum from mild to severe conditions (in order of severity: familial cold autoinflammatory syndrome (FCAS), Muckle-Wells syndrome, neonatal-onset multisystem inflammatory disease/chronic infantile neurologic cutaneous articular syndrome (NOMID/CINCA)), they are summarized in Table 3.

Table 1  Eurofever/PRINTO classification criteria for hereditary recurrent fevers

Legend: FMF: familial Mediterranean fever; MKD: mevalonate kinase deficiency; TRAPS: tumor necrosis factor receptor-associated periodic syndrome; CAPS: cryopyrin-associated periodic syndromes 

Table 2 Eurofever/PRINTO clinical classification criteria for hereditary recurrent fevers and PFAPA

Legend: FMF: familial Mediterranean fever; MKD: mevalonate kinase deficiency; TRAPS: tumor necrosis factor receptor-associated periodic syndrome; CAPS: cryopyrin-associated periodic syndromes; PFAPA: periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis 

Table 3 Comparative view of disorders within the cryopyrin associated periodic syndromes

Legend: FCAS: familial cold autoinflammatory syndrome; WS: Muckle-Wells syndrome; NOMID/CINCA: neonatal onset multisystem inflammatory disease / chronic infantile neurologic cutaneous articular syndrome 

Although not a monogenic disease like the other mentioned conditions, PFAPA syndrome (periodic fever, aphthous stomatitis, pharyngitis, cervical adenitis) is traditionally a member of the periodic fever syndrome family, and it is in fact the most common type of periodic fever syndromes. It usually begins before the age of five, with fever episodes lasting three to five days and occurring approximately every 28 days. Episodes may be accompanied by aphthous stomatitis, tonsillopharyngitis, and cervical lymphadenitis.

The syndrome of undifferentiated recurrent fever (SURF) encompasses a diverse range of autoinflammatory conditions marked by episodic, self-resolving systemic inflammation in the absence of a confirmed genetic diagnosis. It is increasingly identified in individuals experiencing recurrent fever once primary hereditary periodic fever syndromes and PFAPA syndrome have been ruled out. Recent findings indicate that SURF may involve multiple organ systems and that a significant proportion of affected individuals show a full or partial response to colchicine—an effect not as commonly observed in PFAPA syndrome.

4. When to suspect an autoinflammatory disease?

Since there are many autoinflammatory conditions that manifest with a broad spectrum of signs and symptoms that can overlap with those of various autoimmune diseases and immunodeficiencies, and since these are rare disorders, it is far more important to know when to suspect autoinflammatory disease than to know everything in detail about a single entity. Suspicion should be raised in patients with periodic and recurrent fever when infective, autoimmune, and malignant diseases have been excluded. Some autoinflammatory diseases have elements of immunodeficiencies causing recurrent infections. Also, it is good to know that some autoinflammatory diseases manifest without fever, thus the absence of fever is not an exclusion criterion.

The age of disease onset, ethnic origin, and family history are valuable medical data. Although the majority of these diseases begin in infancy, some can manifest for the first time in adulthood. Most of these conditions are not strictly geographically or ethnically linked; also, since many of them are caused by de novo or somatic mutations, in such cases the family history will be unremarkable. Almost all autoinflammatory diseases can be triggered by stress or infection; other triggering factors may be cold, minor trauma, pregnancy, menstruation, immunization, and exercise.

Skin inflammation should be considered as a “red flag” as almost all of these disorders affect the skin. Since the changes are not pathognomonic, a skin biopsy is necessary. Among the more common skin manifestations are non-pruritic urticaria-like changes, refractory to antihistamines, with neutrophilic infiltrates on histology. They can be found in CAPS and Schnitzler syndrome. Pustular dermatoses are found in Behçet disease and CRMO. Painful ulcerations and pyoderma gangrenosum are a part of PAPA syndrome and of very early inflammatory bowel disease. Granulomatous changes are found in Blau syndrome. Interferonopathies are characterized by vasculopathies, panniculitis, lipoatrophy, and frostbite-like changes, especially on the extremities. Plaques are common in FMF and TRAPS patients.

Musculoskeletal manifestations such as permanent or transient arthritis, synovitis, osteitis, and osteomyelitis, especially in cases of sterile pyogenic inflammation, should prompt suspicion of an autoinflammatory condition. Bone deformities and finger clubbing can be seen in severe forms of CAPS and in DIRA syndrome. Lytic and sclerotic bone lesions are a part of CRMO. Monoarthritis is common in FMF and PAPA syndrome, and polyarthritis in sJIA and mevalonate kinase deficiency. Intense myalgia is characteristic of FMF and TRAPS.

Eye manifestations include conjunctivitis, periorbital edema, and uveitis, which occur in most cases of CAPS and TRAPS. Behçet and NOMID cause the most severe eye pathology, which can result in blindness.

Gastrointestinal manifestations include abdominal pain, diarrhea, aphthae, and mucous ulcerations. Peritonitis is common in FMF and TRAPS. Diarrhea is common in mevalonate kinase deficiency, macrophageactivation syndrome, and very early-onset inflammatory bowel disease.

The spectrum of neurological disorders is broad – vasculitis (Behçet disease), hearing loss (CAPS), psychomotor retardation (NOMID, interferonopathies). Convulsions are common in most of periodic fever syndromes.

5. Initial evaluation

The first step in evaluating recurrent fevers involves obtaining a detailed history, which should include:

• Fever pattern (duration, frequency, periodicity, and resolution without treatment)
• Associated symptoms (e.g., pharyngitis, aphthous ulcers, adenopathy, rash, arthralgia, abdominal pain, fatigue)
• Family history of similar febrile episodes, autoimmune, or autoinflammatory diseases
• Response to antipyretics and treatment with corticosteroids
• Environmental exposures, recent infections, and travel history
• Growth and developmental assessment

A meticulous physical examination should assess for signs of chronic illness, lymphadenopathy, hepatosplenomegaly, mucosal lesions, and joint involvement.

In cases where fevers follow a predictable cyclic pattern, periodic fever syndromes should be strongly considered.

5.1. First-Line Investigations

The first-line workup for recurrent fevers aims to rule out infectious, inflammatory, and hematologic causes. Recommended laboratory tests include:

• Complete blood count (CBC) with differential
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
• Serum ferritin (elevated in systemic JIA and hemophagocytic lymphohistiocytosis)
• Immunoglobulin levels (IgA, IgM, IgG, IgE)
• Blood cultures during febrile episodes
• Urinalysis and urine culture
• Liver and renal function tests
• Stool analysis for occult blood and infectious pathogens

Depending on clinical suspicion, additional tests such as tuberculin skin test (TST) or interferon-gamma release assay (IGRA) for tuberculosis and viral serologies (EBV, CMV, adenovirus, enterovirus, parvovirus B19) may be warranted.

Laboratory abnormalities such as leukocytosis, increased CRP, accelerated ESR, and thrombocytosis are common during disease episodes. However, some patients have only a mild increase in CRP, lymphopenia, and leukopenia during exacerbations. An unexplained increase of inflammatory markers, even when there are no other symptoms, should prompt suspicion of an autoinflammatory disease.

During the work-up of a patient with a suspected autoinflammatory disease it is necessary to exclude infection, malignancy, immunodeficiency, and rheumatic disease. A routine laboratory panel consisting of full blood count with differential and peripheral smear, ESR, CRP, electrolytes, urea, creatinine, LFTs, urinalysis, uric acid, and LDH should be ordered. Initial microbiology testing consists of a throat swab, blood culture, urine culture, EBV serology, CMV serology, HIV test, and tuberculosis test. Chest X-ray and abdominal ultrasound are important in the initial work-up. 

Patients should be monitored for the development of amyloidosis by monitoring proteinuria and microalbuminuria.

5.2. Second-Level Investigations

If first-line workup is inconclusive and suspicion for autoinflammatory disease remains, second-level investigations may be needed:

• Next-generation sequencing (NGS) for autoinflammatory gene panels
• Serum amyloid A (SAA) for chronic inflammation and amyloidosis risk
• Extended autoimmunity panel (ANA, RF, ANCA, ENA, anti-dsDNA)
• Bone marrow aspiration if leukemia or HLH is suspected

If available SAA and S100 proteins may be assessed. A negative response to a localized cold challenge, such as the ice cube test, helps distinguish FCAS from cold urticaria. Patients with moderate (MWS) or severe (NOMID/CINCA) forms of the disease often experience progressive sensorineural hearing loss. At the time of diagnosis, all individuals with CAPS should undergo a slit lamp examination and retinal evaluation. While high levels of circulating immunoglobulin D were once considered a key feature of Hyper IgD syndrome, they have limited diagnostic sensitivity and specificity. In contrast, elevated urine mevalonate levels during disease flare-ups—caused by reduced MVK enzyme activity and the buildup of mevalonic acid—are more specific to MKD and can assist in confirming the diagnosis.

Immunoserological tests (ANA, ANCA) should also be done. Depending on the symptoms and differential diagnosis, additional tests can be performed: joint aspiration (to exclude septic arthritis), skin biopsy, audiometry (if CAPS is suspected), whole-body MRI (SAPHO, CRMO), heart ultrasound (FMF, TRAPS), lumbar puncture (CAPS), etc.

Imaging studies such as echocardiography, MRI, or PET-CT may be warranted in selected cases, particularly if systemic inflammation is suspected.

Genetic testing plays a crucial role in diagnosing monogenic autoinflammatory diseases. Next-generation sequencing (NGS) allows for the analysis of:

• Gene panels, covering multiple candidate genes

• Whole-exome or whole-genome sequencing, if broader analysis is required

Genetic variants identified through sequencing are classified as:

• Pathogenic (disease-causing)

• Likely pathogenic

• Variants of uncertain clinical significance

• Likely benign

• Benign

Only pathogenic and likely pathogenic variants have direct diagnostic and therapeutic relevance. Advanced sequencing technologies, such as NGS, have become widely adopted, gradually replacing the traditional Sanger sequencing method, which analyzes genes individually. As a result, NGS is generally the preferred approach. However, in specific cases—such as when a patient has a known familial condition or presents with characteristic disease symptoms—Sanger sequencing of a single gene may be a more cost-effective option. Standard NGS coverage may not always detect somatic mutations, necessitating deep sequencing, though this specialized analysis may not be accessible to all healthcare providers. If routine genetic testing does not yield a definitive diagnosis, patients should be directed to specialized research centers with expertise in molecular diagnostics.

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