Poncet disease, tuberculosis-arthritis: a case report in upper Egypt and a review of the literature

Reactive arthritis in tuberculosis (TB) is known as Poncet’s disease, a rare aseptic form of arthritis characterized by polyarticular impairment observed in patients with active TB, with no evidence of direct bacillary invasion of the joints. The literature related to this syndrome is scarce and restricted to case reports, which contributes to its underdiagnosis. This study aimed at reporting a case of Poncet’s arthritis diagnosed at our hospital, and at reviewing the diagnostic and therapeutic aspects involved; hence, we describe a case of Poncet’s disease in a 13-year-old girl whose reactive arthritis overshadowed other clinical symptoms of TB, resulting in delayed diagnosis and treatment. Anti-TB treatment was initiated. Clinical remission occurred after 2 weeks and the diagnosis of Poncet’s arthritis was established, concluding that taking a thorough medical history and performing relevant examinations and investigations for possible TB, especially in endemic areas, will help expedite the diagnostic process even in the absence of TB symptoms.


Introduction
The incidence of tuberculosis (TB) has increased exponentially. According to the WHO, in 2007, the incidence of new TB cases was 9.27 million [1]; thus, TB remains a major source of morbidity and mortality worldwide [2].
Approximately 10-19% of extrapulmonary TB involves joints and bones [3]. Almost half of these cases are spinal TB, followed by TB arthritis, TB osteomyelitis, and reactive arthritis; the latter, reactive arthritis, is known as Poncet's disease (PD) [4].
PD is a rare syndrome first introduced in 1897 by the Frenchman Antonin Poncet when he described a polyarthritis in an acute stage of TB, which resolved without joint damage. Continuous reports [5] on patients with similar characteristics led authors to improve the definition, and in 1978, Bloxham and Addy defined PD as a parainfective arthritis [1], but its existence has been questioned; however, more cases have been reported over the years.
PD is characterized by articular affection in patients diagnosed with TB, not related to direct invasion by the micro-organism, but to an immune reaction to the tuberculous protein, constituting a reactive arthritis. This case is reported because of its rarity, and in a TBendemic area of a country such as Upper Egypt, one should keep this possibility in mind in patients with polyarthritis, as early recognition of this complication is of major importance to avoid delayed initiation of appropriate treatment [6].
Case report A case of PD was identified together with the Rheumatology, Chest, and Neurology Departments at Aswan University Hospital, Egypt. A 13-year-old female student presented to Aswan University Hospital, Rheumatology & Physical Medicine Department, referred by a chest physician, complaining of pain and swelling of both knee joints for the last 15 days without a relevant medical history except for admission with a 10day history of chills, fever, and widespread myalgia 3 months before presenting; she denied any respiratory symptoms. Patient consent was obtained from her guardian (father).
On elaborating, pain and swelling involved both knees and the left ankle (started with pain, followed by swelling 2 days later); the involvement of joints was simultaneous; there was difficulty in using the above joints, and other joints were not involved.
The patient was hospitalized, and additional laboratory testing was performed, which was negative for mononucleosis, toxoplasmosis, cytomegalovirus, salmonellosis, brucellosis, and HIV; acute rheumatic fever was excluded because of noncompletion of the modified Jones criteria. She was referred for ophthalmic consultation, which was negative for signs of iridocylitis.
The patient was started on Brufen tablets 400 mg twice daily, and a week later, the patient was still complaining of pain and swelling of the left knee and ankle, with painful symmetrical skin rashes on the medial side of both knees; she reported that her mother applied a topical cream without physician advice, which was seen by a dermatologist and diagnosed as erythema nodosum. A synovial fluid analysis was made of the left knee, revealing no crystals. Standard cultures and cultures for TB of the synovial fluid, the blood, and the sputum were negative. Radiography of the knee and ankles showed no abnormalities apart from soft-tissue swelling. Autoimmune laboratory tests including rheumatoid factor, anticyclic citrullinated peptide, and antinuclear antibodies were negative. A routinely ordered chest radiography showed bilateral hilar lymphadenomegaly. A chest computed tomographic scan was performed, showing multiple mediastinal and hilar lymph nodes with no focal lesion on the lung parenchyma; these findings on computed tomography were interpreted as a possible TB infection. The tuberculin skin test was measured as 30 mm. A PCR for TB was carried out on the patient's sputum, which was found to be positive; a diagnosis of pulmonary TB and PD was made, and isoniazid, rifampicin, pyrazinamide, and ethambutol were started; the patient became afebrile and her joint pain improved within the following 15 days, with complete resolution of all symptoms after 6 weeks of treatment, including joint pain and swelling (Figs 1-4).

Discussion and review
TB is a very prevalent disease in developing countries including Egypt. Approximately 10-19% of the extrapulmonary TB cases affect bones and joints, Figure 1 At presentation, bilateral knee arthritis, with symmetric painful rashes over the front and the medial sides of both knees.

Figure 2
At presentation, normal radiography in both knees.

Figure 3
At presentation, a chest radiography showed only increased bronchopulmonary markings with no focal lesions.
corresponding to 1-3% of all cases of TB [3]. This possibility becomes increasingly important as the careless use of corticosteroids, immune suppressants, or biologicals as the treatment for misdiagnosed arthritis can trigger the reactivation or the dissemination of the disease [1].
It is widely known that tubercular septic monoarthritis, in which Mycobacterium tuberculosis may be isolated from the joint, may complicate TB infection; however, active TB may be complicated by a sterile reactive arthritis that is less known and therefore often missed [7]. PD is used to indicate an aseptic polyarthritis, presumably a reactive arthritis, developing in the presence of active TB elsewhere. Although PD is considered as a reactive arthritis, the clinical presentation of PD differs from the classical pattern of reactive arthritis [8]. In contrast to reactive arthritis, the onset of symptoms in PD before the start of arthritis is much longer than just a few weeks, whereas the resolution of arthritis upon starting of adequate antituberculous therapy is mostly within a few weeks, and chronic arthritis has never been reported in PD [7]. In PD, oligoarticular or polyarticular impairment is more frequent than monoarticular impairment, similar to other reactive arthritis, involving mainly the large joints, such as knees, ankles, and hips, often accompanied by articular effusion. There is no microbiological evidence of the Mycobacterium spp. invasion in the affected join [9]. In our patient, serological tests for autoimmunity were negative, and the tuberculin test and acute-phase proteins, were altered.
The differential diagnosis of the case was one of the following: [10,11] (1) Viral arthritis: Rubella involves mainly small joints.  Two weeks of antitubercular therapy, no arthritis, and improved rashes.
disease and ulcerative colitis), and normal pregnancy. (6) Chronic arthritis: Initial presentation: systemic lupus erythrematosis and rheumatoid arthritis: criteria not fulfilled.

Conclusion
The differential diagnosis of patients at risk for TB presenting with arthritis should definitely include PD. The diagnosis of PD remains clinical, and is established on excluding other potential causes of arthritis in a patient with active TB. The complete resolution of arthritis of PD on antitubercular therapy also provides further proof of the diagnosis.

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Conflicts of interest
There are no conflicts of interest.