Case
A 76-year-old female presented with recurrent overnight hypoglycaemia and impaired hypoglycaemia awareness. Her past medical history included stage 5 chronic kidney disease and bipolar affective disorder. Formal 72-hour fast elicited severe symptomatic hypoglycaemia (1.0mmol/L) at 20 hours following commencement, with low C-peptide 245 pmol/L, undetectable insulin levels, low beta-hydroxybutyrate 0.14 mmol/L, undetectable insulin antibodies and sulfonylurea levels, suggestive of non-islet-cell tumour hypoglycaemia (NICTH). Due to the severity of the hypoglycaemia, she was treated with intravenous glucose, with complete resolution of symptoms. Due to lack of a commercially available assay, insulin-like growth factor 2 (IGF-2) level was not performed. Positron emission tomography/computed tomography (PET-CT) showed prominent focal FDG avidity in the appendix suspicious for malignancy. Laparoscopic appendicectomy was performed with histology revealing a 2.5mm gastrointestinal stromal tumour (GIST), staining positive for IGF-2. Following surgery, no further episodes of hypoglycaemia occurred.
Discussion
NICTH is a rare but important aetiology of hypoglycaemia in individuals without diabetes mellitus [1-4]. It is seen in a wide range of tumours and has been frequently described in GISTs [2,3,5-7]. However, only large tumours have been reported with the majority exceeding 10 cm [4,7-10].
The diagnosis of NICTH is made through a combination of biochemical testing with a 72-hour fast, as well as additional findings of elevated IGF-2 and IGF-2:IGF-1 ratio, which can be falsely low in individuals with renal failure [1,2,5,7-9,11]. The role of histopathology is not clear but increasingly described with a recent systematic review describing 65.9% patients staining positive to IGF-2 [4].
Complete resection of the tumour is considered curative, with other medical therapies such as glucocorticoids being less effective [2,5,8,9].
Despite the non-availability of IGF-2 levels, the combination of consistent 72-hour fast results, histopathology findings and complete response post-surgery underpin an unusual and novel case of NICTH caused by a small 2.5mm GIST.