Locomotor disease

Locomotor disease

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There are about 200 different musculoskeletal conditions that affect the muscles, ligaments, tendons, bones, and joints. Examples include simple muscle strains and broken bones to wear and tear osteoarthritis and back pain, and on to more serious conditions such as rheumatoid arthritis (RA), tendonitis, Behçet’s syndrome (rare), systemic lupus erythematosus, gout (and other crystal-induced arthritides), carpal tunnel syndrome, juvenile idiopathic arthritis (JIA), joint hypermobility, osteoporosis, Paget’s disease of bone, polymyagia rheumatica (PMR), fibromyalgia, polymyositis and psoriatic arthritis. Symptoms range from mild discomfort to debilitating pain. Arthritis, in more than 100 subtypes, is amongst the most common musculoskeletal conditions, causing inflammation, pain and varying levels of immobility/disability.

The professional version of the Merck Manual provides quite detailed information about Musculoskeletal and Connective Tissue Disorders suitable for medical students.

Disease-modifying anti-rheumatic drugs (DMARDs)

Different types of arthritis (rheumatic disease) are treated with different drugs. The aim of the clinician is to prescribe drugs which improve symptoms and, where possible, slow or halt progress of the condition. As their name suggests, disease-modifying anti-rheumatic drugs (DMARDs) offer benefit via the latter mechanism. Full therapeutic response to DMARDs may take several months to become evident. Early intervention with DMARD therapy is recommended to control the signs and symptoms of rheumatic disease and to limit joint damage.

There are two main categories: conventional DMARDs and biological therapies. This topic covers conventional DMARDs, biological therapies are described in the Biological DMARDs topic.

Conventional DMARDs include:

Methotrexate is an oral medication prescribed for moderate to severe RA.

Gold (as sodium aurothiomalate) is given by deep intramuscular injection for active progressive RA. This is a long-term treatment, requiring regular dosing up to 5 years post-complete remission. Second courses of gold are not usually effective if the patients suffers a complete relapse.

Penicillamine has a similar action to gold. Penicillamine should be discontinued if there is no improvement within 1 year.

Sulfasalazine is prescribed for active RA on expert advice.

Hydroxychloroquine is prescribed for active RA on expert advice. 

 

Because of their toxicity, these next immunosuppressants are only used for RA when patients have not responded to other DMARDs:

Ciclosporin, a calcineurin inhibitor: only prescribed for severe active RA when conventional second-line therapy is inappropriate or ineffective.

Leflunomide is a pyrimidine synthesis inhibitor which regulates autoimmune lymphocytes. Used by specialist practitioners for treating moderate to   severe active RA and active psoriatic arthritis.

Cyclophosphamide: can be prescribed for RA with severe systemic manifestations and other connective tissue diesases (e.g. active vasculitis).

Azathioprine can be prescribed for RA that has not responded to other DMARDS.

Prescibers should consider co-morbidity and patient preference when choosing which DMARD (or combination of DMARDs) to prescribe. Whilst providing similar efficacy as intramuscular gold and penicillamine, methotrexate or sulfasalazine are often better tolerated. Gold and penicillamine can be effective in palindromic rheumatism. Methotrexate is generally prescribed alongside at least one other DMARD, and often short-term corticosteroid treatment for newly diagnosed RA.

Tofacitinib is an immunomodulating agent and DMARD with a novel mechanism of action. It selectively inhibits the activity of Janus kinase 3 (JAK3), a hematopoietic cell-restricted mediator of cytokine, growth factor, and interferon signalling via the JAK-STAT pathway. Inhibition of JAK3 appears to disrupt development and function of T, B, and NK cells. The FDA has approved tofacitinib for use in the management of moderate to severe active RA in patients who have shown an inadequate response or intolerance to methotrexate. Tofacitinib can be used alone or in combination with methotrexate or other nonbiologic DMARDs, although concomitant use with biologic DMARDs (e.g. adalimumab, certolizumab pegol, etanercept, golimumab, infliximab, anakinra or rituximab), selective costimulation modulators (abatacept), and the anti-interleukin-6-receptor monoclonal antibody tocilizumab, is not recommended. Concomitant use with other immunosuppressive agents  (e.g. azathioprine or cyclosporine) is also not recommended. Serious, sometimes fatal infections (including cryptococcosis, pneumocystosis, tuberculosis and other mycobacterial infections, esophageal candidiasis, multidermatomal herpes zoster, cytomegalovirus infection, BK virus infection) have been reported. Tofacitinib treatment should not be initiated in patients with active infections.