A 56-year-old woman presented with the chief complaint of right knee pain that had been ongoing for 8 months. Eight months earlier, the patient had visited a different clinic to seek treatment for the same symptoms, was treated with medications, including NSAIDs, but the pain worsened. When visiting our clinic, she complained of pain and swelling in both proximal interphalangeal joints, metacarpophalangeal joints, with morning stiffness in the right knee for 2-3 hours. We checked her laboratory findings, including radiographs of the knee and hands for confirmation of an inflammatory, autoimmune disease. The laboratory results indicated that the patient had an increased lymphocyte count (51%), a normal level of erythrocyte sedimentation rate/C-reactive protein, and a negative reading for rheumatoid factor, human leukocyte antige-B 27. Upon physical examination of the right knee, the patient had knee swelling, a soft click, and a positive reading on the Mcmurray test. From the radiographs of the knee, a mild narrowing of the medial joint with minimal osteophytes was noted (Fig. 1). We made an initial diagnosis of pathologic plica syndrome with a suspiciously torn medial meniscus that was indicative of an autoimmune disease such as RA; for this reason, a follow-up arthroscopy was performed. From the arthroscopic findings, we determined that the patient had a generalized villous synovitis and a torn medial meniscus (Fig. 2). A synovectomy was performed with a biopsy with partial meniscectomy. One week after the operation, the biopsy of the synovium was confirmed by a pathologist as villous hyperplasia with lymphocytic infiltration that favored RA. Based on the patient's history, physical examination, and synovial biopsy, we made the diagnosis of rheumatoid arthritis and treated the patient with medications, including NSAIDs and DMARDs. Three days later, the patient visited our outpatient office complaining of severe diarrhea and general weakness. The patient's lactose intolerance was discovered after her patient history was reevaluated. All of her current medications were stopped, and drugs that did not contain lactose were administered after her diarrhea abated. As a results, her symptoms improved.

Lactose intolerance is the inability to properly digest lactose, a sugar found in milk and milk products. Lactose intolerance is caused by a deficiency of the enzyme lactase, which is produced by the cells lining the small intestine. Lactase breaks down lactose into 2 simpler forms of sugar called glucose and galactose, which are then absorbed into the bloodstream. The lack of this enzyme may cause a range of abdominal symptoms, including stomach cramps, bloating, and flatulence. In addition, as with other unabsorbed sugars (such as sorbitol, mannitol, and xylitol), the presence of lactose and its fermentation products raises the osmotic pressure of the colon contents, and causes diarrhea. Not all people with lactase deficiency have digestive symptoms, but those who do may have lactose intolerance. Most people with lactose intolerance can tolerate some amount of lactose in their diet.5)

The treatment of RA is strongly dependent on the lifelong use of NSAIDs, oral steroids, COX-2 inhibitors, and DMARDs. Many patients find it difficult to swallow tablets and hard gelatin capsules and, thus, do not comply with the prescription. This results in a high incidence of noncompliance and ineffective therapy.6) Fast dissolving and fast dispersing drug delivery systems may offer a solution to these problems, and as a result, fast disintegrating tablets (FDT) are gaining prominence as a new drug-delivery system. Other reasons for the need of FDT are the requirements to meet current needs of the industry, like improved solubility, stability, and bioavailability enhancement of poorly absorbed drugs. Various technologies and techniques have been used to manufacture FDT, including freezing, drying, lyophilization, tablet molding, direct compression, spray drying, sublimation, and the addition of superdisintegrants, such as lactose monohydrate, and mannitol.7,8) In many studies, the effect of lactose excipients on FDT was studied and reported on improving the results of drugs with regard to disintegration time and stability. Therefore, most of the recent medication, especially NSAIDs and DMARDs, contain lactose and mannitol.

There are no reports about medication for newly diagnosed RA of lactose intolerance patients, because lactose intolerance has been thought to not cause particular problems with most existing RA therapies. From the experience of the authors, this case that resulted in stopping the RA medication because of severe diarrhea is thought to be different from general lactose intolerance patients, but additional studies are required. Currently, approximately 30-50% of the domestic Korean population is lactose intolerant, and the number of people suffering from RA is increasing annually. Through the studies of these 2 diseases, we should be able to understand patients in whom these complications occur as the result of medication that contains small amounts of lactose and mannitol. With this knowledge, a proper prevention protocol can be created.