Fever with polyarthritis and rash encompasses a large number of differentials which may include infectious causes, e.g., dengue, chikungunya, viral hepatitis, TB, etc., and autoimmune conditions, e.g., systemic lupus erythematosus, rheumatoid arthritis, Still’s disease, etc., along with malignancies (predominantly hematological) and drug reactions/serum sickness [1]. Poncet’s disease comprises of polyarthritis probably due to tubercular rheumatism where no mycobacterial involvement can be demonstrated in the joints [2]. It usually presents with a nondestructive symmetric polyarthritis and some school of thought suggests the entity as a parainfective reactive arthritis. The diagnosis is challenging and Poncet’s disease is essentially a diagnosis of exclusion. A high index of suspicion may be required to identify this rare complication and early initiation of treatment is essential, as it responds dramatically to anti-tubercular therapy [3]. The pathogenesis of Poncet’s disease is yet to be fully understood. It has been proposed that a vigorous immune response to mycobacteria occurs within the joints, followed by activation of T cells that leads to cross-reactivity between mycobacterial antigens with cartilage proteoglycans. Molecular mimicry between mycobacterial heat shock proteins and human heat shock proteins have also been suggested [4]. Poncet’s disease has been reported with extrapulmonary TB, but very rarely associated with pulmonary TB.

A 15-year-old boy was suffering from a low grade fever with evening rise of temperature for six months. Fever was associated with cough and mucoid expectoration for two months along with bilateral symmetrical polyarthritis involving knees, ankles, wrists. However, there was no history of hemoptysis, weight loss, night sweats. He started to experience occasional, colicky abdominal pain with reddish rash distributed over his lower limbs and buttocks seven days prior to his admission. His mother had a history of pulmonary TB six years back and had completed the full course of treatment.

On examination he was pale, febrile with a tender soft to firm lymph node in right upper cervical chain. A maculopapular red rash in both lower limbs and buttocks suggestive of palpable purpura (Figure 1). Chest examination revealed coarse crackles in right mammary area. Tender swollen bilateral symmetrical joints (knees, elbows, and wrists) with diminished range of motion was also found.

Initial investigations revealed—Hemoglobin = 8.3 g/dl, total leucocyte count = 4200 (neutrophil 65%, lymphocyte 33%, monocyte 2%), platelet 2.5 lakhs/cmm³, erythrocyte sedimentation rate = 86 mm first hour, peripheral blood smear—normocytic, normochromic anemia, corrected reticulocyte count = 2.3%, C-reactive protein 7.0 mg/l (Figure 2). Contrast enhanced computed tomography (CT) scan thorax revealed intracavitory lesion with adjacent tree in bud infiltrates noted in the right middle and lower lobe suggestive of secondary TB with endobronchial spread (Figure 3). Ultrasonography of the affected joints showed synovial thickening with minimal effusion in right knee joint. Synovial fluid analysis revealed cell count: 5000 cells/mm³ (lymphocyte predominant) with no crystals, negative cultures and all stains were negative. Cartridgebased nucleic acid amplification test of synovial fluid was negative. Skin biopsy revealed perivascular infiltration of fragmented neutrophils and lymphocytes, features suggestive of leukocytoclastic vasculitis (Figure 4). Direct immunofluorescence (DIF) revealed IgA deposition in the cutaneous vessel wall, suggestive of IgA vasculitis/HSP.

The patient was put on Category 1 anti-tubercular therapy as per Revised National Tuberculosis Control Program (RNTCP) recommendations and the drugs were supplied according to weight-based fixed dose combination. As per his body weight of 45 kg, he was started on three tablets daily of fixed dose combination (FDC) for intensive phase of treatment. Each tablet comprised of Isoniazid (75 mg), Rifampicin (150 mg), Pyrazinamide (400 mg), and Ethambutol (275 mg). After initiation of therapy, his symptoms improved dramatically, the rash resolved spontaneously within two days and the polyarthritis resolved over a few days.

Hence he was diagnosed to be a case of Poncet’s disease with IgA vasculitis.

Tubercular rheumatism/Poncet’s disease is a nondestructive oligo/polyarticular joint disease where mycobacteria are not demonstrable in the joint tissue, and is considered as a musculoskeletal manifestation of TB, and associated with extrapulmonary manifestation commonly TB lymphadenitis [5]. The disease is commonly seen in juveniles and young adults predominantly females with symmetrical peripheral polyarthritis involving large joints [6]. Association of Poncet’s disease though common with extrapulmonary TB has been associated with active pulmonary TB as reported by Garg et al. [7].

Pathogenesis of Poncet’s disease involves a reactive arthritis, mediated by a hypersensitivity reaction against tuberculoprotein probably due to molecular mimicry between mycobacterial antigens and host tissues (mainly heat shock protein, 65) that cross-reacts with human heat shock protein [8].

Diagnostic criteria for Poncet’s disease as published by Sharma et al. may be used after excluding other possible explanations of inflammatory arthritis [9].

Poncet’s disease is a reactive arthritis in the presence of active TB, although a synovial biopsy is definitive. Poncet’s disease and erythema nodosum may be the two sides of the same coin with different expressions of similar immunopathology [10]. However, in our case nonerosive polyarthritis which resolved with initiation of anti-tubercular therapy could not be attributed to any other cause apart from Poncet’s disease.

The etiology of HSP may be contributed to many causes like upper respiratory tract infections, subacute bacterial endocarditis, viral hepatitis, systemic lupus erythematosus, malignancies, TB, acquired immunodeficiency syndrome, hypersensitivity reaction to drugs/immunization, etc. [11]. The leukocytoclastic vasculitis with palpable purpura, typically on the lower extremities and buttocks is highly suggestive of IgA vasculitis. The histopathology suggestive of IgA vasculitis includes destruction of small vessels characterized by a transmural inflammatory infiltrate consisting of neutrophils, endothelial swelling, fibrin deposition, red blood count (RBC) extravasation. However, immune complexes may also play a primary role in the pathogenesis of Henoch–Schönlein vasculitis. Initially, deposition of immunoglobulin or immune complexes in the vessel walls activates alternative complement pathway and leads to subsequent generation of chemotactic factors with neutrophilic infiltration. Phagocytosis of these immune complexes may provoke release of destructive lysosomal enzymes leading to vessel wall injury, thrombosis, and hemorrhage. Deposition of IgA, IgG, IgM along with complement and fibrin was reported in the dermis and mesangium [12]. The cause of the rash in our case could have been due to tuberculosis induced vasculitis/other causes which demanded extensive evaluation but the typical colicky abdominal pain with a maculopapular rash in lower limbs and buttocks, supported by histopathological findings of skin biopsy clinched the diagnosis of IgA vasculitis/HSP. As per literature is concerned, Islek et al. reported an association of pulmonary TB with HSP in pediatric population. However, there are other case reports which have established a link between disseminated tuberculosis and IgA vasculitis [13].

Poncet’s disease is a nondestructive oligo/polyarthritis usually associated with extrapulmonary tuberculosis. Mechanism is probably a reactive arthritis mediated by hypersensitivity to tuberculoprotein. We hereby report a case of Poncet’s disease with pulmonary TB. Association of Poncet’s disease with HSP has rarely been reported, but in this case we could establish a diagnosis of Poncet’s disease with pulmonary TB and IgA vasculitis/HSP. Hence, clinicians must be cautious while dealing a situation with constellation of such symptoms.