Splenic lymphoid hyperplasia in a cat presenting with hyperammonaemia, hypercalcaemia and hypercobalaminaemia

A 5-year-old, male neutered, Bengal-cross cat presented with progressive neurological signs (ataxia and torticollis). Initial haematology, serum biochemistry and electrolytes (including calcium) were unremarkable; however, ammonia was markedly elevated. Portosystemic shunting and hypocobalaminaemia were ruled out (cobalamin levels were markedly elevated) and there was no organic aciduria. Hyperammonaemia was medically managed, but later, seizures developed, at which time the cat was found to have severe hypercalcaemia. Parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) levels decreased. Computed tomography angiography demonstrated unusual contrast uptake within the spleen (‘zebra-stripes’). Histopathology of the spleen demonstrated diffuse lymphoid follicular hyperplasia. Post-splenectomy, hypercalcaemia and hyperammonaemia both resolved (hypercobalaminaemia persisted). The cat remained bright and well after 8 years of splenectomy. This is the first report of hypercalcaemia associated with splenic lymphoid hyperplasia. In this case, both PTH and PTHrP were low, suggesting that hypercalcaemia was mediated via an alternative mechanism.