Cyclophosphamide in the Treatment of Refractory Proliferative Arachnoiditis in CNS Tuberculosis

Tubercular arachnoiditis occurring as a late complication of TBM is due to immune mediated reactions and is usually treated with high doses of corticosteroids. In the investigators' experience patients have received corticosteroids upto a duration of 20-28 months. In such cases, if the patient is refractory to corticosteroids, it is logical to step up to cyclophosphamide rather than continuing to give high dose steroids only similar to other immune mediated conditions such as CIDP, systemic and CNS vasulitis, Lupus nephritis etc.

Cyclophosphamide has been used most widely in the management of Lupus nephritis and maximum experience with the drug has been in this indication. So the dosage and duration of administration has been adapted from the induction phase dosing schedule of the ACR guidelines for the management of Lupus nephritis. The guidelines recommend 500 to 1000 mg/m2 BSA of cyclophosphamide. So the investigators decided to use 750 mg/m2 of the drug rounded off to the higher 50 mg.

Pathogenesis of tubercular arachnoiditis and Possible mechanism of cyclophosphamide Tubercular arachnoidiitis is a delayed complication in most cases due to inflammation in the optochiasmatic, spinal and other cranial nerves leading to neurologic deficits. In such situations, it is seen that there is an initial improvement in clinical symptoms followed by deterioration due to enlargement of lesions or appearance of new lesions, especially in patients with extrapulmonary tuberculosis. These new lesions are probably due to immune mediated mechanisms-it has been seen that in more than 95% of cases are drug sensitive and corticosteroids are the cornerstone of management of such patients. The complete pathogenesis of immune medicated tissue injury in tuberculosis has not been elucidated. Various studies have shown that there is an excess of pro-inflammatory cytokines and chemokines including TNF-alpha and interleukins that lead to recruitment of inflammatory cells and an exhuberant immune response in patients who develop these complications as compared to those who don't. There have been studies which have shown genetic polymorphisms in the genes encoding pro-inflammatory and anti-inflammatory cytokines-leading to difference in response to corticosteroids like LTA4 (Leukotriene- A4 hydrolase) gene. It is also well known that various immune mediated diseses such as SLE, multiple sclerosis etc are triggered by viruses and other infections. It is routine practice to treat acute bacterial meninigitis and tubercular meningitis with dexamethasone, which is again a steroid and immunosuppressant along with specific antibiotics or anti-tubercular therapy respectively based on evidence from systematic reviews and meta-analysis. Neurocysticercosis is treated with corticosteroids and other immunosuppressant medications such as methotrexate as recommended in guidelines, adalimumab and eternacept used as steroid sparing agents. Various other immune mediated complications of acute and chronic infections such as dengue myocarditis, ADEM etc are also treated with immunosuppression including corticosteroids. Lepra reactions in Leprosy are also treated using steroids, thalidomide, methotrexate, azathioprine, cyclophosphamide, cyclosporine etc.

In recent times, the corticosteroid- Dexamethasone has been shown to have mortality benefit in patients with moderate to severe COVID, proven in a randomized controlled trial. Simliarly, even though there are no RCT data, Tocilizumab, siltuximab and other immunosuppressant medications have been approved for emergency use based on their efficacy shown in large case series in COVID-19.

Justification for the use of cyclophosphamide this study:

Cyclophosphamide is a potent immunosuppressant agent. It is used in Lupus and other immune mediated conditions and has been shown to be effective in randomized controlled trials in Lupus nephritis, granulomatous polyangiiitis etc. Though it is widely used off label in various inflammatory immune mediated neurologic conditions such as CNS vasculitis, CIDP, multiple sclerosis, autoimmune encephalitis, refractory myasthenia gravis etc, the evidence for this is basically derived from the rheumatology and nephrology literature. It has to be emphasized that all the data for immunosuppression with azathioprine, cyclophosphamide, mycophenolate mofetil, methotrexate, calcineurin inhibitors in various immune mediated conditions have been derived from renal transplant/solid organ transplant cohorts, lupus nephritis cohorts, systemic vasculitis cohorts and inflammatory bowel disease cohorts. The various guidelines issued by the professional bodies for these conditions form the principles of treatment of rare conditions such as neuroimmunologic diseases. The major adverse effects of concern in patients on Cyclophosphamide is the occurrence of life threatening infections such as tuberculosis. It has been seen that patients on high dose corticosteroids and cyclophosphamide are at higher risk of infection than those on steroids alone or on neither drug.Though the risk of TB increases with administration of immunosuppressants, the mainstay of management is early diagnosis and starting appropriate therapy and not cessation of immunosuppression. In the context of SLE the occurrence of infection is also dependent on various other factors such as disease activity, previous exposure to tuberculosis etc. The Americal college of rheumatology guidelines do not say anything on the course of action in case patients develop infections. There are no professional guidelines for the management of infections in patients on cyclophosphamide. There are no RCTs on the most appropriate form of ATT regimens or the modification of immunosuppression in these conditions. There are various case series and case reports who have been systematically studied infections and their management including the large prospective EuroLupus cohort. None of these authors advice complete cessation of immunosuppression in patients who develop infections including tuberculosis. The guidelines for management of tuberculosis such as British thoracic society guidelines for the management of TB in CKD,do not suggest cessation of immunosuppression in post renal transplant patients. The guidelines clearly mention that TB in patients with CKD have to be treated in same lines of immunocompetent patients, and the anti-tubercular drugs may need to be given in renal modified doses. In case of tuberculosis risk, it has been shown by various long term follow up studies that a considerable proportion of patients with latent TB infections progress to develop active TB post transplantation or after treatment with immunosuppressants or biologic agents such as anti TNF therapy. In such circumstances, the guidelines suggest not dropping immunosuppression, but treatment of latent TB or active TB. The guidelines for the management of active TB in solid organ transplantation suggests early diagnosis and treatment of tuberculosis along with increasing the dose of immunosuppressants such as corticosteroids, cyclosporine or tacrolimus as the ATT regimen containing rifamycins tend to induce the metabolism of these immunosuppression and trough levels of calcineurin inhibitors have to be maintained by increasing the dose of cyclosporine or tacrolimus by upto 4-5 times.

These recommendations are mainly based on a large multicentre cohort of more than 2000 patients derived from 187 publications who had received solid organ transplantation and developed tuberculosis, where the dose of immunosuppressant drugs had been increased to maintain adequate blood levels to avoid rejection of the organ graft. Similar recommendations have been made by the TBNET consensus statement for management of Tuberculosis in transplant recipients.

The management of immunosuppression in these cases are mainly based on expert consensus in other conditions such as rheumatoid arthritis, spondyloarthropathy etc. The TBNET consensus statement also says that in case the organ is not vital or the infection is life threatening, it may be considered to reduce the level of immunosuppression. The guidelines for the use of anti TNF-α therapy is clearer in this aspect. While the occurrence of active TB during anti TNF-α therapy warrants withholding (NOT cessation) of immunosuppression, it may be re started 2 months after ATT the if patients demonstrate a favorable response to anti-TB therapy and require early resumption of anti TNF therapy.The BTS guidelines suggest that if active TB was diagnosed prior to starting of "Anti-TNF-α therapy, treatment should not be commenced for at least 2 months after antituberculosis treatment with full compliance has begun, supervised by a thoracic physician orinfectious disease specialist, and until the drug susceptibility profile of the organism in those with positive cultures is known, as a minimum." However, if the patient develops TB while on anti TNF therapy the anti-TNF-α treatment can be continued if clinically indicated because the patient would otherwise be prevented from receiving the continued clinical benefit to their underlying disease and may have a flare up or major clinical deterioration. The rationale provided by these guidelines is that HIV positive individuals with reduced CD4 counts and clinical TB, who are even more immunosuppressed than those on anti-TNF-a treatment, respond just as well to TB treatment as those who are HIV negative. Taking that logic forward, it may be reasonable to start therapy with cyclophosphamide three months after starting standard Anti tubercular therapy in patients with tubercular meningitis who have shown clearcut improvement followed by deterioration due to development of arachnoiditis and paradoxical immune responses.