Residency · Residency · Rheumatology

Autoinflammatory Syndromes - FMF and Beyond

Introduction

Autoinflammatory diseases represent a distinct category of immune-mediated disorders driven by dysregulation of the innate immune system, characterized by unprovoked, recurrent episodes of systemic inflammation. Unlike autoimmune diseases, which are mediated by adaptive immunity with high-titer autoantibodies and autoreactive T cells, autoinflammatory diseases lack these features and instead arise from aberrant activation of innate immune pathways, particularly those involving inflammasome assembly and interleukin-1 production. The autoinflammatory disease spectrum encompasses monogenic disorders caused by single-gene mutations, including familial Mediterranean fever, cryopyrin-associated periodic syndromes, TNF receptor-associated periodic syndrome, and hyperimmunoglobulinemia D with periodic fever syndrome (also known as mevalonate kinase deficiency). Additionally, polygenic or complex autoinflammatory conditions include Behcet disease, PFAPA syndrome, gout, and adult-onset Still disease. The IL-1 pathway is central to the pathogenesis of many autoinflammatory diseases, and the development of IL-1 blockade has transformed the therapeutic landscape for these conditions.

Classification Framework

Inflammasomopathies

The inflammasomopathies are autoinflammatory diseases driven by aberrant inflammasome activation leading to excessive IL-1 production and neutrophilic inflammation. The NLRP3 inflammasome-mediated disorders comprise the cryopyrin-associated periodic syndrome spectrum, which includes familial cold autoinflammatory syndrome, Muckle-Wells syndrome, and neonatal-onset multisystem inflammatory disease (also known as chronic infantile neurological cutaneous and articular syndrome). The pyrin inflammasome-mediated disorders include familial Mediterranean fever, in which mutations in the MEFV gene lead to constitutive pyrin inflammasome activation. In all inflammasomopathies, the final common pathway is overproduction of IL-1beta, which drives neutrophilic tissue inflammation.

Non-Inflammasomopathies

The non-inflammasomopathies encompass autoinflammatory disorders driven by pathways other than direct inflammasome activation. TNF receptor-associated periodic syndrome arises from mutations in TNFRSF1A, leading to aberrant NF-kB signaling. Blau syndrome similarly involves NF-kB pathway dysregulation. Hyperimmunoglobulinemia D with periodic fever syndrome results from mutations in the mevalonate kinase gene, disrupting the mevalonate pathway. The interferonopathies, including stimulator of interferon genes-associated vasculopathy with onset in infancy and Aicardi-Goutieres syndrome, are driven by excessive type I interferon production. Proteasome dysfunction disorders, such as chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (also termed proteasome-associated autoinflammatory syndrome), arise from defects in the ubiquitin-proteasome pathway.

Familial Mediterranean Fever (FMF)

Epidemiology and Genetics

Familial Mediterranean fever is the most common monogenic autoinflammatory disease worldwide, with a prevalence of approximately 1:200 to 1:1000 in at-risk populations, including individuals of Turkish, Armenian, Arab, and Jewish descent. The disease follows autosomal recessive inheritance, caused by mutations in the MEFV gene located on chromosome 16, which encodes the pyrin protein. Several common pathogenic mutations have been identified, with M694V associated with the most severe phenotype and highest amyloidosis risk, followed by M680I and V726A. The E148Q variant has low penetrance and may represent a polymorphism rather than a truly pathogenic mutation. Homozygosity for M694V confers the most severe phenotype, with frequent attacks, early onset, and the greatest risk for developing AA amyloidosis.

Pathogenesis

Pyrin functions as an innate immune sensor that is normally maintained in an inactive state through phosphorylation by RhoA GTPase-mediated kinase signaling. MEFV mutations result in constitutive activation of the pyrin inflammasome, which drives caspase-1 activation and subsequent overproduction of IL-1beta and IL-18. This excessive IL-1 production triggers neutrophilic inflammation in serosal surfaces and joints, producing the characteristic attack pattern. The mechanism of colchicine, the cornerstone therapy for FMF, involves disruption of microtubules, which blocks both pyrin inflammasome assembly and neutrophil chemotaxis. Chronic elevation of serum amyloid A, an acute phase reactant driven by persistent IL-1-mediated inflammation, leads to deposition of AA amyloid in the kidneys, gastrointestinal tract, and liver, representing the most serious long-term complication of inadequately treated FMF.

Clinical Manifestations

The clinical hallmark of FMF is recurrent, self-limited episodes of fever and serosal inflammation lasting 12 to 72 hours. These episodes are often stereotypical for individual patients, following a characteristic pattern. Peritonitis is the most common serosal attack, occurring in approximately 95 percent of patients, and presents as diffuse abdominal pain that can closely mimic an acute abdomen. Many patients undergo unnecessary appendectomy or exploratory laparotomy before the diagnosis of FMF is established. Pleuritis manifests as unilateral chest pain and is self-limited. Arthritis presents as acute monoarthritis predominantly affecting large joints such as the knee and ankle, and is typically self-limited, although chronic destructive arthritis of the hip can occur rarely, particularly in patients with M694V homozygosity who experience protracted attacks. Erysipelas-like erythema, an erythematous, sharply demarcated rash on the lower legs and feet that is typically unilateral, is considered pathognomonic for FMF. Febrile myalgia syndrome is a protracted myalgia that can mimic polyarteritis nodosa. The most serious long-term complication is AA amyloidosis, which manifests primarily as renal amyloidosis progressing from nephrotic syndrome to end-stage renal disease. Risk factors for amyloidosis include M694V homozygosity, male sex, SAA gene polymorphisms, and inadequate colchicine therapy. Phenotype II FMF refers to the rare presentation in which amyloidosis is the first manifestation, occurring without prior clinical attacks.

Diagnosis

The diagnosis of FMF relies on clinical criteria supported by genetic testing. The Tel-Hashomer criteria identify typical attacks consisting of fever with serositis and incorporate supportive criteria including family history, ethnic background, age of onset before 20 years, and response to colchicine. The Eurofever/PRINTO classification criteria published in 2019 provide an evidence-based framework applicable to pediatric populations. Genetic testing with MEFV sequencing is valuable but not always diagnostic, as approximately 30 percent of patients have only one identifiable mutation; clinical diagnosis remains valid in these cases. During attacks, inflammatory markers are characteristically elevated, including CRP, ESR, serum amyloid A, fibrinogen, and white blood cell count with neutrophilia. Between attacks, CRP usually normalizes, but SAA may remain elevated, indicating subclinical inflammation that drives amyloidosis risk.

Management

Colchicine is the cornerstone of FMF therapy, dosed at 1 to 2 mg daily in adults and titrated to control attacks and normalize serum amyloid A levels. It prevents attacks in more than 90 percent of patients and, critically, prevents amyloidosis even in patients who continue to have breakthrough attacks. Colchicine must be taken continuously rather than on an as-needed basis. It is safe during pregnancy and breastfeeding. The most common side effect is diarrhea, which is dose-limiting; rare adverse effects include myopathy, neuropathy, and cytopenias. A crucial drug interaction to recognize is the concurrent use of CYP3A4 inhibitors such as clarithromycin and cyclosporine, which can precipitate life-threatening colchicine toxicity. For the approximately 5 to 10 percent of patients with colchicine-resistant FMF, IL-1 blockade represents the next therapeutic step. Anakinra at 100 mg subcutaneously daily offers rapid onset and is effective for both breakthrough attacks and amyloidosis prevention. Canakinumab at 150 mg subcutaneously every 4 to 8 weeks demonstrated efficacy in the CLUSTER trial for colchicine-resistant FMF and has received approval in the European Union. Rilonacept, an IL-1 trap, is an alternative option. For individual attacks, management includes colchicine dose escalation, NSAIDs, and short-course glucocorticoids for protracted episodes.

<image>A clinical presentation and pathogenesis diagram of Familial Mediterranean Fever. Top panel: Show the pyrin inflammasome pathway - normal pyrin inhibited by RhoA kinase phosphorylation → mutant pyrin (MEFV mutation) with impaired inhibition → constitutive inflammasome assembly → caspase-1 activation → IL-1beta and IL-18 release → neutrophilic inflammation. Mark colchicine's point of action (disrupting microtubule-dependent inflammasome assembly) and anakinra/canakinumab blocking IL-1. Bottom panel: Show a patient figure with typical FMF manifestations - recurrent fever episodes on a timeline (12-72 hour attacks at irregular intervals), peritonitis (diffuse abdominal pain), pleuritis (unilateral chest pain), monoarthritis (swollen knee), erysipelas-like erythema (red, demarcated rash on shin), and amyloidosis (kidney with amyloid deposits in glomeruli, stained with Congo red showing apple-green birefringence). Include mutation severity spectrum: E148Q (mild) → V726A → M680I → M694V (most severe).</image>

Cryopyrin-Associated Periodic Syndromes (CAPS)

Spectrum (Mild to Severe)

The cryopyrin-associated periodic syndromes represent a continuous spectrum of disease severity caused by gain-of-function mutations in the same gene. Familial cold autoinflammatory syndrome is the mildest form, characterized by cold-triggered urticarial rash, fever, and arthralgia, with onset typically in infancy. Muckle-Wells syndrome occupies an intermediate position on the severity spectrum, featuring urticarial rash, fever, arthritis, and sensorineural hearing loss, with an approximate 25 percent risk of developing AA amyloidosis. Neonatal-onset multisystem inflammatory disease, also known as chronic infantile neurological cutaneous and articular syndrome, represents the most severe phenotype, manifesting from birth with chronic urticarial rash, central nervous system inflammation including chronic aseptic meningitis and papilledema, epiphyseal overgrowth producing characteristic joint deformities, and severe developmental delay if untreated.

Genetics and Pathogenesis

All CAPS disorders follow autosomal dominant inheritance, caused by gain-of-function mutations in the NLRP3 gene (also known as CIAS1). These mutations result in constitutive NLRP3 inflammasome activation and excessive IL-1beta production. De novo mutations are common in NOMID, accounting for approximately 50 percent of cases. Somatic mosaicism, in which NLRP3 mutations are present at low levels detectable only by deep sequencing, explains some clinically diagnosed cases with negative standard genetic testing.

Management

IL-1 blockade has been transformative for all forms of CAPS, dramatically altering the natural history of these diseases. Canakinumab at 150 mg subcutaneously every 8 weeks is FDA-approved for CAPS. Anakinra at 1 to 2 mg/kg/day subcutaneously is an effective alternative. Rilonacept at 160 mg subcutaneously weekly (with a 320 mg loading dose) is another option. For NOMID, lifelong IL-1 blockade is required to prevent progressive neurologic damage; patients also need hearing aids for sensorineural hearing loss. Monitoring should include serum amyloid A, CRP, audiometry, ophthalmologic examination, and brain MRI for NOMID patients.

TNF Receptor-Associated Periodic Syndrome (TRAPS)

Clinical Features

TRAPS follows autosomal dominant inheritance, caused by mutations in the TNFRSF1A gene encoding the TNF receptor 1. A distinguishing clinical feature is the duration of febrile episodes, which last 1 to 4 weeks, considerably longer than the 12 to 72 hour attacks of FMF. The rash of TRAPS is characteristic: migratory erythematous patches that demonstrate centrifugal migration accompanied by underlying myalgia. Periorbital edema is a distinctive feature that, when present, should raise strong suspicion for TRAPS. Other manifestations include serositis, arthralgia, and abdominal pain. AA amyloidosis develops in 10 to 15 percent of patients, particularly those with cysteine mutations in the TNFRSF1A gene.

Management

Unlike FMF, colchicine is generally ineffective in TRAPS. Glucocorticoids are effective for controlling acute attacks but tachyphylaxis frequently develops, necessitating escalating doses. IL-1 blockade has become the first-line long-term therapy, with canakinumab being preferred based on randomized controlled trial evidence, while anakinra is also effective. Etanercept provides partial responses in some patients, which is paradoxical given that it blocks TNF signaling, but it may work by reducing TNF receptor shedding. Anti-IL-6 therapy with tocilizumab has shown benefit in isolated case reports.

Hyperimmunoglobulinemia D with Periodic Fever Syndrome (HIDS) / Mevalonate Kinase Deficiency (MKD)

Clinical Features

HIDS, the milder form of mevalonate kinase deficiency, follows autosomal recessive inheritance caused by mutations in the MVK gene encoding the mevalonate kinase enzyme. Febrile episodes last 3 to 7 days and are accompanied by cervical lymphadenopathy, which is pathognomonic for HIDS among the monogenic autoinflammatory diseases. Other features include abdominal pain, arthralgia, skin rash, and aphthous ulcers. Attacks can be triggered by vaccinations, infections, and stress. Serum IgD is elevated above 100 IU/mL in approximately 80 percent of patients, though this finding is not specific; IgA is also commonly elevated. Mevalonic aciduria represents the severe end of the MKD spectrum, manifesting with psychomotor retardation, cataracts, failure to thrive, and carrying high mortality.

Pathogenesis

Reduced mevalonate kinase activity leads to decreased synthesis of geranylgeraniol, which in turn impairs RhoA GTPase function and results in pyrin inflammasome activation. This pathway converges with the same downstream mechanism as FMF, explaining the shared features of IL-1-driven inflammation.

Management

Canakinumab has demonstrated efficacy in MKD and is approved for this indication based on the CLUSTER trial. Anakinra provides an alternative IL-1 blockade option. Glucocorticoids and NSAIDs can be used for acute attack management. Colchicine produces variable responses. Notably, statins are paradoxically contraindicated as they may worsen the disease by further reducing mevalonate pathway flux.

Adult-Onset Still Disease (AOSD)

Clinical Features

Adult-onset Still disease presents with a characteristic pattern of quotidian (daily) spiking fevers, typically reaching 39 to 40 degrees Celsius before returning to baseline or below. The evanescent salmon-colored macular rash appears during fever spikes and fades as the temperature normalizes; it demonstrates a positive Koebner phenomenon. Arthritis is polyarticular and can become destructive, with a particular predilection for the wrists and a tendency toward carpometacarpal joint ankylosis. Sore throat is a common early feature that frequently triggers an infectious workup before the correct diagnosis is considered. Serositis, including pleuritis and pericarditis, occurs in a significant proportion of patients. Hepatosplenomegaly and lymphadenopathy may be prominent. Macrophage activation syndrome, the most feared complication, develops in approximately 12 to 17 percent of AOSD patients and carries high mortality.

Laboratory

The laboratory profile of AOSD is distinctive. Ferritin is markedly elevated, exceeding 1000 ng/mL in more than 70 percent of patients; levels above 10,000 ng/mL should raise immediate concern for macrophage activation syndrome. Glycosylated ferritin below 20 percent is suggestive of Still disease, as ferritin is normally 50 to 80 percent glycosylated. Leukocytosis with neutrophilia is characteristic. ESR and CRP are elevated. Rheumatoid factor and antinuclear antibody are characteristically negative, a finding that helps distinguish AOSD from other conditions. Liver function tests may be elevated, reflecting hepatic involvement.

Classification: Yamaguchi Criteria (most sensitive)

The Yamaguchi criteria, which are the most sensitive classification criteria for AOSD, require 5 or more criteria to be met, including at least 2 major criteria. Major criteria include fever of 39 degrees Celsius or higher lasting at least 1 week, arthralgias or arthritis lasting at least 2 weeks, the typical evanescent rash, and leukocytosis of 10,000 or higher with at least 80 percent granulocytes. Minor criteria include sore throat, lymphadenopathy or splenomegaly, liver dysfunction, and negative ANA and RF. The criteria require exclusion of infections, malignancy, and other autoimmune diseases.

Management

Glucocorticoids, typically prednisone at 0.5 to 1 mg/kg/day, are effective for most patients as initial therapy, though many become glucocorticoid-dependent. Methotrexate is the first-line steroid-sparing agent and is particularly effective for the chronic articular phenotype. IL-1 blockade with anakinra at 100 mg subcutaneously daily is highly effective for systemic features, producing rapid responses; canakinumab offers a longer dosing interval as an alternative. IL-6 blockade with tocilizumab is effective for both systemic and articular manifestations. TNF inhibitors are less effective than IL-1 or IL-6 inhibitors for the systemic features of AOSD. Management of macrophage activation syndrome requires high-dose glucocorticoids, cyclosporine, and anakinra, with intravenous immunoglobulin reserved for refractory cases.

<image>A diagnostic approach flowchart for recurrent fever syndromes in adults and children. Start with "Recurrent episodes of fever + systemic inflammation (elevated CRP, SAA, WBC)." First branch: Duration of attacks. Short attacks (12-72 hours): Consider FMF (serositis, erysipelas-like erythema, monoarthritis; MEFV testing) or HIDS/MKD (cervical lymphadenopathy, elevated IgD; MVK testing). Intermediate attacks (3-7 days): Consider HIDS/MKD or PFAPA (periodic fever, aphthous stomatitis, pharyngitis, adenitis in children; responds to single-dose prednisone). Prolonged attacks (1-4 weeks): Consider TRAPS (migratory rash, periorbital edema; TNFRSF1A testing). Daily spiking fevers: Consider AOSD (quotidian fever, salmon rash, ferritin >1000, negative ANA/RF). Chronic from birth: Consider CAPS/NOMID (urticarial rash, SNHL, CNS inflammation; NLRP3 testing). For each entity, show the first-line treatment: FMF → colchicine; CAPS → canakinumab; TRAPS → canakinumab; HIDS → canakinumab; AOSD → anakinra or tocilizumab.</image>

PFAPA Syndrome

Periodic fever, aphthous stomatitis, pharyngitis, and adenitis (PFAPA) syndrome is the most common periodic fever syndrome in children, though it rarely persists into adulthood. It is distinguished by its clockwork periodicity, with fevers recurring every 3 to 6 weeks and lasting 3 to 5 days per episode. The dramatic response to a single dose of prednisone at 1 mg/kg is near-pathognomonic and can be used diagnostically when the clinical picture is consistent. Tonsillectomy is curative in approximately 70 to 80 percent of affected children. No genetic test exists for PFAPA; it remains a clinical diagnosis based on the characteristic periodic pattern and associated features.

Key Clinical Pearls

• Colchicine prevents AA amyloidosis in FMF even when breakthrough attacks persist; NEVER discontinue
• FMF peritonitis mimics acute abdomen; many patients undergo unnecessary surgery before diagnosis
• CAPS exists on a severity spectrum (FCAS → MWS → NOMID); all respond dramatically to IL-1 blockade
• Glycosylated ferritin <20% is highly suggestive of Still disease; total ferritin >1000 with negative RF/ANA should trigger consideration
• PFAPA responds dramatically to a single dose of prednisone; this response can be used diagnostically
• Cervical lymphadenopathy during fever episodes is characteristic of HIDS/MKD among the monogenic AIDs

References

1. Ozen S, et al. Eurofever/PRINTO classification criteria for familial Mediterranean fever, mevalonate kinase deficiency, TNF receptor-associated periodic syndrome and cryopyrin-associated periodic syndromes. Ann Rheum Dis. 2022;81(7):907-921.
2. De Benedetti F, et al. Canakinumab for the treatment of autoinflammatory recurrent fever syndromes (CLUSTER trial). N Engl J Med. 2018;378(20):1908-1919.
3. Lachmann HJ, et al. Use of canakinumab in the cryopyrin-associated periodic syndrome. N Engl J Med. 2009;360(23):2416-2425.
4. Feist E, et al. Mechanisms, biomarkers and targets for adult-onset Still's disease. Nat Rev Rheumatol. 2018;14(10):603-618.
5. Ben-Chetrit E, Levy M. Familial Mediterranean fever. Lancet. 1998;351(9103):659-664.

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