A 4-year-old male child presented with excessive urine output and increased frequency of micturition. He had complaints of increased thirst and fluid intake for 6 months. There was no history of trauma, autoimmunity and tuberculosis, joint pain and deformity. DI was confirmed with water deprivation test and decreased random urine osmolality value of 77.00 mosm/kg (normal serum osmolality: 295.00 mosm/kg). Urine specific gravity was 1.005. Magnetic resonance imaging (MRI) showed a uniformly thickened pituitary stalk that enhanced on contrast administration. There was no other cranial pathology detected. All investigations performed to rule out the common causes for DI with a thickened pituitary stalk in pediatric population were within normal limits. These tests included chest radiograph, complete hemogram, erythrocyte sedimentation rate, serum electrolytes, blood sugar, and glycosylated hemoglobin and were within the normal range. The anti-diuretic hormone (ADH) level was 0.30 pg/mL and was in the subnormal range. The serum human chorionic gonadotrophin (hCG), acetylcholine esterase (ACE) and 1,25(OH)2 vitamin D3 were within normal limits. Antinuclear antibody and antipituitary antibodies were negative. The anterior pituitary hormonal profile included cortisol 18.0 mug/dL, adrenocorticotrophic hormone (ACTH) 45.6 pg/mL, tri-iodothyronine (T3) 142.0 mug/dL, tetra-iodothyronine (T4) 8.2 mug/dL, thyroid stimulating hormone (TSH) 3.15 muIU/mL, growth hormone (GH) 0.7 ng/mL and prolactin 27.0 ng/mL. Lumbar cerebrospinal fluid (CSF) cytology was normal and CSF ACE and HCG were negative. In spite of extensive investigations, no definitive etiology for the central DI and thickened infundibulum could be established, and hence the patient was kept under regular follow-up. Repeated neurological and ophthalmological examinations were performed to detect progression of the disease. The DI was treated medically with nasal desmopressin spray and the clinical response was immediate with decrease in urine output and resolution of nocturnal enuresis.
After 6 months, the child developed a left scalp swelling. At this stage, he had no history of fever, lethargy, skin eruptions or weight loss and examination did not reveal any lymphadenopathy and hepatosplenomegaly. The computed tomography (CT) scan of the brain showed two punched out lytic lesions in the skull with soft tissue swelling [Figure 1]. MRI brain showed a persistent thickened pituitary stalk in addition to confirming CT findings [Figure 2]. Histological examination of biopsy of the skull lesion revealed the tumor to consist of malignant tumor cells arranged as plump spindles and giant multinucleate cells [Figure 3]. Inflammatory cells including eosinophils were seen between the tumor cells. Immunohistochemistry (IHC) demonstrated the tumor cell positivity for CD1a and S-100. The histology was diagnostic of LCH. A bone scan using Tc99m MDP injection showed osteolytic lesion in left parietal bone and osteoblastic lesions in both the frontal bones suggesting skull involvement, but no evidence of osteoblastic lesion was seen in rest of the skeletal system. Bone marrow aspiration showed normocellular areas with trilineage hematopoiesis, no increase in blasts and no granulomas. Liver biopsy showed no infiltration of liver by LCH. His chest X-ray was clear and skeletal survey did not show any other lesion. After confirming the diagnosis and extent of disease, the child was planned for chemotherapy according to LCH protocol. The patient was given six cycles of initial treatment of injection vinblastin at a dosage of 6 mg/m2 at an interval of 1 week for each cycle. The continuation treatment consisted of injection vinblastin at the same dosage every third week and tablet omnacortil at a dosage of 40 mg/m2 from day 1 to day 5 every third week and tablet 6-mercaptopurine (MP) at a dosage of 50 mg/m2 on all days except Sundays for a total duration of 12 months including the initial treatment.