Amelanotic primary thalamic melanoma: a case report.

BACKGROUND

Primary thalamic melanoma is an exceptionally rare malignant tumor of the central nervous system (CNS). The amelanotic subtype presents additional diagnostic challenges because of its nonspecific neuroimaging features, which frequently result in diagnostic delays and poor clinical outcomes. CASE PRESENTATION: A 25-year-old East Asian woman presented with a one-month history of persistent headache, dizziness, and vomiting. A lumbar puncture revealed significantly elevated intracranial pressure exceeding 500 mmH₂O. Cranial magnetic resonance imaging (MRI) showed nonspecific signal abnormalities in the right dorsothalamic region, with no enhancement on gadolinium-contrast scans. Cytological examination of the cerebrospinal fluid (CSF) initially showed no evidence of malignant cells. One month after admission, positron emission tomography–magnetic resonance imaging (PET-MRI) revealed markedly increased radiotracer uptake in the right thalamic lesion. Repeat CSF cytology detected atypical cells, and immunohistochemical staining was positive for SOX-10, S100, Melan-A, and HMB-45, confirming the diagnosis of amelanotic PDLM. Despite aggressive therapeutic interventions, the patient’s condition deteriorated rapidly, and she passed away four months after symptom onset.

CONCLUSIONS

This case highlights the considerable challenges associated with the early diagnosis of amelanotic primary thalamic melanoma. For patients presenting with unexplained intracranial hypertension and nonspecific central nervous system involvement, clinicians should maintain a high index of suspicion for this rare entity, even when characteristic imaging findings are absent. Repeated cerebrospinal fluid cytological and immunohistochemical examinations are essential for establishing a definitive diagnosis. The integration of molecular diagnostic approaches may further enhance early detection and facilitate individualized therapeutic strategies.