An unusual cause of a discharging sinus.(Rheumatology)

A 37 year old man presented to the orthopaedic outpatient department complaining of a white liquid discharge coming out of the front of his right leg. Physical examination revealed that he had a discharging sinus on the anterior aspect of middle thirds of his right leg draining a milky white fluid with a viscosity of that of water. There was an area of 3 x 2 cm around the sinus that was indurated. Radiography of the leg showed a radio-opaque lesion in the subcutaneous tissue (fig 1). No irregularity or abnormality was detected in either bone of the leg. Bacteriological examination of the fluid was negative as was the KOH mount done to exclude a fungal infection. His blood counts were neutrophils 76%, lymphocytes 20%, monocytes 2%, eosinophils 2%, and his blood cultures were negative. Blood chemistry, renal function, and liver function were all normal. Detailed examination of other extremities and their radiological surveys were non-informative. A fine needle aspiration cytology (FNAC) smear was taken and revealed a few red blood cells against a proteinaceous background. An incision biopsy was planned but on incision, only some chalky white fluid identical to the discharge was drained out. Histopathological examination of the material duplicated the FNAC findings. Alizarin red S staining demonstrated characteristic birefringence.

[FIGURE 1 OMITTED]

QUESTIONS

(1) What is the diagnosis?

(2) What other features can be associated with the present clinicoradiological picture?

(3) Which immunological test is positive in a majority of patients with this clinical condition?

Q1: What is the diagnosis?