To emphasize the identification of distinctive paraneoplastic syndromes as the first manifestation of Merkel cell carcinoma (MCC) with unknown primary.

MCC is a rare neuroendocrine tumor  arising from the Merkel’s cells in the basal layer of the epidermis. It histologically resembles small cell lung carcinoma and stains positively for CK20.Biopsy-proven MCC in lymph nodes in the absence of identifiable primary tumor is classified as  MCC with unknown primary. Paraneoplastic cerebellar degeneration (PCD) and  Lambert-Eaton syndrome (LEMS) ,in association with Anti-Hu and voltage-gated Calcium P/Q antibodies, can frequently be seen in MCC.  We illustrate a rare case of MCC with unknown primary, manifested by LEMS and PCD.  

Case report.

86-year-old man with history of basal cell carcinoma (left ear) s/p Moh's surgery (3 years prior to presentation) admitted with 2-months of progressively worsening fatigue and difficulty walking leading to wheelchair dependency  (previously able to walk 2-miles daily ).He had intermittent diplopia with down beating rotatory nystagmus, bilateral dysmetria, truncal ataxia, intermittent bowel/bladder incontinence, and mild dysphagia. He had no cutaneous findings suspicious for a primary skin malignancy. MRI brain revealed generalized cerebral atrophy. MRI spine showed incidental  congenital cervical spinal canal stenosis with mild cord compression. CT chest/abdomen/pelvis showed no malignancy but revealed bilateral axillary lymphadenopathy with biopsy consistent with diagnosis of MCC (CK20+). Paraneoplastic panel was positive for P/Q-type voltage-gated calcium channel  antibody consistent with LEMS. Lumbar puncture unremarkable except for elevated CSF protein (70). He received steroids followed by chemotherapy (Carboplatin/Etoposide), IV immunoglobulin (for 5-days), and physical therapy with significant clinical improvement and discharge to rehabilitation facility.

Neurologic findings such as cerebellar ataxia and LEMS without clear etiology should prompt a workup for a paraneoplastic syndrome which may precede tumor diagnosis. MCC can present as occult lymph node involvement without primary cutaneous findings.