Systemic lupus erythematosus is a rare disease affecting predominantly young women. In 11–18 % of cases, the symptoms appear later, between 50th and 65th year of life [11]. Even more exceptional is the incidence of symptoms similar to SLE that are the result of action of certain groups of drugs. This form of SLE is called drug-induced lupus erythematosus (DILE). It is generally equally common in older males and females, probably because of their multiple drug exposure. Typical manifestations of drug-induced SLE are milder than in the idiopathic form. DILE is defined by development of symptoms similar to SLE, finding of positive antinuclear antibodies; it usually resolves on cessation of the offending drug.

DILE differs from SLE by a different antibody profile and a more favourable prognosis, with a lower variety of antibodies and predominance of the anti-histone ones [1]. Certain antibodies typically associated with the idiopathic SLE were occasionally identified also in drug-induced lupus (e.g. Coombs antibody, lupus anticoagulant, antiphospholipid antibodies).

In the past DILE was best described in patients using hydralazine, procainamide, methyldopa and chlorpromazine. Although the use of these drugs has a decreasing tendency, the incidence of drug-induced SLE remains the same, mainly due to new drugs with a potential to induce this syndrome, such as quinidine, minocycline, carbamazepine, ticlopidine and tumour necrosis factor inhibitors, e.g. infliximab, etanercept and adalimumab. DILE has been reported as an adverse effect after administration of more than 40 drugs and their number is continuously growing [12]. Drug-induced lupus is generally a rare condition, with an estimated incidence in the USA of about 30,000 cases per year, but the number of medications that may induce it is growing [10].

Clinical symptoms of DILE are similar to those in the idiopathic form. Diagnosis of drug-induced lupus is confirmed based on lupus-specific findings, such as 11 diagnostic criteria for lupus. However, in most patients, less than four of these criteria required for the SLE diagnosis are found. These criteria must be met during the use of the drugs known to cause DILE. It should be noted that a positive antinuclear antibody (ANA) is not enough to establish the DILE diagnosis. For instance, up to 50 % of patients using higher doses of hydralazine will have a positive ANA finding, but only 10 % of them develop drug-induced lupus. The time between drug exposures to onset of symptoms varies from months to years after initiation of the drug treatment, and the symptoms resolve after cessation of the offending drug [9]. Joints are affected in more than 80 % of patients, with myalgia and arthralgia prevailing over arthritis. Common symptoms include unrest, subfebrile temperature and weight loss. Serositis and pneumonitis are typical of DILE caused by procainamide. Skin involvement, renal impairment and neurological disorders are rare in the classical DILE form [3].

DILE diagnosis is usually based on a high ANA titre (>1:1280); these ANA antibodies are directed against deoxyriboproteins, most often against histones. Antibodies against double-stranded DNA are rarely detectable and serum complement levels are usually within the normal range. DILE may be associated with findings, such as leukopenia, lymphopenia and hemolytic anaemia, quite often also lupus anticoagulant and antiphospholipid antibodies. Thrombosis and antiphospholipid syndrome are rare. Anti-histone antibodies are common both in DILE and SLE and cannot be therefore used to distinguish these two conditions.

DILE is generally considered to be a limited disorder the symptoms of which typically disappear several weeks after discontinued use of the offending medication, although positive ANA antibodies and other serological abnormalities persist much longer and completely disappear by up to 12 months. In addition to discontinued use of the respective medication, DILE treatment is mainly symptomatic and consists in the use of NSAIDs and sometimes also corticosteroids, mainly in case of severe cytopenia or pleural and pulmonary symptoms. Only rarely symptoms persist for more than a few months. Some patients respond favourably to treatment with antimalarial drugs; however, in such case it may be an initial manifestation of idiopathic SLE rather than DILE [9].