Case Presentation: Patient is a 74-year-old male with type 2 diabetes complicated by neuropathy, lumbar spinal stenosis with radiculopathy, and venous insufficiency who presented to the ED for evaluation of several months of waxing and waning bilateral lower extremity weakness with progression of symptoms causing multiple falls. Initial CT head revealed an 11 mm acute hemorrhage involving the superior vermis and adjacent right cerebellar hemisphere. CTA with no evidence of high flow vascular malformation in the region of the hematoma. The location of the lesion did not adequately explain his symptoms, so he was admitted to the Neurology service. Further workup with MRI brain demonstrated multiple small areas of enhancement concerning for leptomeningeal metastases with small hemorrhages, with the largest lesion at the superior cerebellum. MRI spine showed avid leptomeningeal enhancement throughout the lumbar, thoracic, and cervical spine, most prominently of the cauda equina, without intramedullary spinal cord enhancement. Given these findings, leptomeningeal neoplastic disease was favored over granulomatous inflammation or infection; however, it was unclear where the primary neoplasm originated. CT torso revealed only a small lung nodule in the right lower lobe. Lumbar puncture demonstrated lymphocytic dominant pleocytosis with elevated protein and low glucose. Cytology was negative for malignancy. Extensive infectious workup was negative. Over his hospital course, he had worsened weakness and became non-ambulatory. He developed a lower extremity DVT. Given high suspicion for leptomeningeal carcinomatosis, especially in the setting of thrombosis, he was transferred to the General Medicine-Oncology service ~hospital day 14 for further work up. Upon transfer, initial physical exam was remarkable for a suspicious asymmetric brown lesion at the nail bed of his left index finger. He disclosed prior trauma to the area and thought the skin changes were related to injury. On further questioning, he did notice the lesion had expanded over the last year. Dermatology was urgently consulted for biopsy. He had an IVC filter placed in lieu of anticoagulation for DVT to mitigate risk of intracranial hemorrhage. Skin biopsy was positive for pT2a acral lentiginous melanoma. While awaiting biopsy results, he also had a second lumbar puncture, with cytology confirming metastatic melanoma as etiology of his leptomeningeal enhancement.
Discussion: Our patient was diagnosed with malignant acral melanoma with isolated metastases to the leptomeninges. Malignant melanoma has one of the highest incidences of leptomeningeal involvement among all solid tumors, with rates as high as 10-15% of patients with advanced melanoma (1-2). However, it is extremely rare to have metastases to the leptomeninges in the absence of additional sites of metastasis. Retrospective analyses have found concurrent brain metastases in 60-85% of all patients with malignant melanoma with leptomeningeal involvement (3-7). Unfortunately, the presence of leptomeningeal involvement in melanoma conveys a poor prognosis with a mean overall survival of 3.5 months, even with aggressive treatment (3).
Conclusions: This case highlights a rare and highly advanced inpatient presentation of a common outpatient diagnosis, metastatic malignant melanoma. As generalists, it serves as a humbling reminder of the importance of a thorough physical exam in the pursuit of diagnostic accuracy.