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.

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.

[1] Aspirated synovial fluid is usually sterile[2] but will sometimes show elevated cell count (>100 cells/mL) with 50% being polymorphonuclear leukocytes.

Mattingly suggests that IH may be an unusual variant of rheumatoid arthritis, and some patients may go on to develop RA.

[1] With regard to the periodic nature of effusions, Reimann theorises that: “…either an inherent rhythm or a feedback mechanism (Morley, 1970) excites 'bioclocks' in the hypothalamus or in the synovial membrane (Richter, 1960).

These 'Zeitgebers' provoke sudden accumulation of plasma in the lining and spaces of joints, tendon and ligament sheaths.”[5] There is no specific test for this condition.

More aggressive treatments such as synovectomy, achieved using intra-articular agents (chemical or radioactive) can provide good results, with efficacy reported for at least 1 year.

Local steroid injections can also reduce fluid accumulation short-term, but do not prevent onset of episodes.

[1] A single case report of a patient with treatment-refractory IH describes the use of anakinra, an interleukin 1 receptor antagonist.

[11] A recent single case report has shown hydroxychloroquine (300 mg daily) to be effective too.

[10] (2) Top and Cross used single doses of intra-articular radioactive gold in 18 patients with persistent effusions of mixed causes including 3 with IH.

[5] It affects men and women equally[2] although some publications suggest the condition is slightly more prevalent in females.

When the condition was first being reported in scientific journals, IH was classified as either ‘symptomatic’ or ‘idiopathic’ (of unknown cause).

[1][2][4] Today, a primarily auto-immune cause predominates literature with speculation that IH may be an inherited condition [citation needed] On the basis that IH is periodic in its presentation, early researchers proposed links with malaria where symptoms are also cyclical, even though the two have different duration cycles.

[2] Physiotherapy,[1] surgery, exclusion diets (following allergen testing) have similarly shown no particular success in early reports of IH.