Staging by bone marrow biopsy and computed tomography of the abdomen and pelvis showed no spread of disease. The patient was treated with six cycles of systemic chemotherapy with cyclophosphamide, doxorubicin, vincristine and prednisolone and four infusions of anti\CD20 monoclonal antibody rituximab. lymphomas, whereas primary peripheral nervous system lymphomas are distinctly unusual. Rarer still is an isolated mononeuropathy as a manifestation of neurolymphomatosis: only eight cases of primary sciatic nerve lymphoma have been reported. We describe a patient with solitary infiltration of the left sciatic nerve by a diffuse large B cell lymphoma and discuss this case with reference to the literature. Case report A 55\year\old man presented to his local hospital in November 2001 with weakness and pain in his left foot. Eighteen months previously, he noted his inability to curl the toes of ADU-S100 (MIW815) his left foot. This was associated with numbness of the sole of the same foot. A diagnosis of tarsal tunnel syndrome was made. His symptoms remained unchanged until ADU-S100 (MIW815) July 2002, when he developed intermittent tightening in his left calf. Four months later, he presented to the National Hospital for Neurology and Neurosurgery, London, UK. He was unable to stand on the toes of his left foot, and the numbness had spread to the whole left sole and the back of the leg. He had developed severe pain in the back of his left thigh, radiating down to the ankle, very similar to the sciatica he had experienced 10?years previously on the right side. He was well systemically. On examination, the neurological abnormalities were confined to his left leg. No wasting was evident, but there was severe weakness in the muscle groups innervated by the tibial nerve and numbness in the S1 dermatome. All deep tendon reflexes were intact and the plantar responses flexor. General examination was unremarkable other than a pigmented lesion on his back. Blood tests, including full blood count and erythrocyte sedimentation rate, were normal. Nerve conduction studies showed an absent left posterior tibial motor response from abductor hallucis, with a normal left common peroneal motor amplitude from extensor digitorum brevis (4.2?mV at ankle). The left sural sensory action potential was 16?V initially, but fell to 6?V in a month. Electromyography showed denervation changes in the gastrocnemius and abductor hallucis, but not tibialis anterior, consistent with a tibial or sciatic nerve lesion. Magnetic resonance imaging (MRI) of the lumbosacral spine was normal, but MRI of the thighs showed diffuse swelling and oedema of the sciatic nerve from below the buttock to the level of ADU-S100 (MIW815) the popliteal fossa on the left. The extent of swelling was thought to be unusual for a neurogenic tumour (fig 1A,B?1A,B). Open in a separate window Figure 1?T2\weighted magnetic resonance imaging of the thighs (A, B). High signal is present in the left sciatic nerve as compared with the right in coronal (A) and axial sections (B) (arrows), consistent with an infiltrating mass. High signal extends throughout the length of the sciatic nerve and is associated with swelling and oedema in the surrounding muscle. Fascicular biopsy of the sciatic nerve (CCF), immunostained Rabbit Polyclonal to C-RAF (phospho-Ser301) with anti\CD20 (C), PGP9.5 (D) and Ki\67 (E). The endoneurium is heavily infiltrated with large pleomorphic cells immunoreactive for CD20 and some surrounding blood vessels (C). Remaining small, largely unmyelinated fibres, in Remak bundles (arrow heads), persist throughout the tumour (D). Ki\67 staining shows a proliferation index of nearly 100% (E). 1\m resin sections show a few degenerating myelinated fibres (arrow) and a few persisting small myelinated fibres (large arrowhead) interspersed with the numerous abnormal tumour cells (small arrowheads) (F). Scale bars 40?m (CCE) and 20?m (F). Cerebrospinal fluid (CSF) was normal except for oligoclonal bands, matched in CSF and serum. The pigmented pores and skin lesion within the patient’s back was eliminated and found to be a malignant melanoma of low metastatic potential (Clark level 2, Breslow thickness 0.5?mm). Positron emission tomography showed high uptake in the sciatic nerve area, but also in the top lobe of each lung. Large\resolution computed tomography of the thorax showed ill\defined ground glass shadowing, but no mass lesion. Non\malignant lymphocytes were found by bronchoalveolar lavage. Collectively, the pulmonary findings were compatible with sarcoidosis. A fascicular biopsy of the sciatic nerve lesion was carried out. Haematoxylin and eosin\stained sections of the biopsy showed that the solitary.