Head Scratcher: A Skull Base Lesion without Definitive Diagnosis

Case Description: In July 2015, a 44-year-old woman presented to her local hospital with left otalgia and headache. Shortly thereafter, she was found to have a large nasopharyngeal/skull base lesion involving the left nasopharynx, temporal fossa, cavernous sinus, and petrous temporal bone. She had previously undergone three separate biopsies without a definitive diagnosis. Four months later, she developed diplopia, trismus, headache, left facial tingling and pain, neck pain, left sided hearing loss, nausea, vomiting, and an unintentional 37-pound weight loss. Physical examination revealed left trigeminal hypoesthesia, left abducens paralysis, absence of hearing on the left, severe trismus with minimal mouth opening, and firm and tender left level II lymphadenopathy. Audiogram indicated left profound sensorineural hearing loss (SNHL). A fine needle aspiration of this mass was nondiagnostic, revealing only mixed inflammatory infiltrate. A bone marrow biopsy in 2015 revealed only hypercellular bone marrow with myeloid hyperplasia, but no features of a lymphoproliferative disorder. An ensuing endonasal endoscopic excisional biopsy of this nasopharyngeal mass only revealed benign mucosal and submucosal tissue with marked acute and chronic inflammation, but no evidence of a neoplasm. Flow cytometry was unremarkable. She was subsequently started on antibiotics and high-dose prednisone with significant improvement in her diplopia & trismus. In March 2016, she developed new onset bilateral lower extremity neuropathy with a truncal rash of many small circular hyperpigmented papules. She was started on gabapentin and was evaluated by rheumatology, whereupon ANA, ANCA, and IgG4 values were all unremarkable. Further laboratory workup revealed markedly elevated IgG at 1730 mg/dL (767–1,590 mg/dL). Her kappa/lambda ratio was not elevated. Serum and urine protein electrophoresis were not performed. Her serum creatinine was generally unremarkable, and alkaline phosphatase had been consistently elevated, up to 189 IU/L (44–121 IU/L).

CT and MRI on initial presentation. In May 2024, she returned with improvement of her symptoms and dramatic reconstitution of bone at the central skull base, clivus, and lateral wall of the cochlea. She remains with profound left SNHL. Presently, she is being managed conservatively and undergoing evaluation for hearing rehabilitation.

CT & MRI in March 2024.

Discussion: This patient had an unusual skull base lesion which initially caused significant morbidity but greatly improved with demonstration of remineralization of bone and improvement of subjective symptoms despite conservative and expectant management only. Various laboratory values and imaging over time raises concern for a few possible hematologic/lymphoproliferative etiologies, with no well-fitting diagnosis. Solitary plasmacytoma and IgG monoclonal gammopathy of undetermined significance (MGUS) are promising differential diagnoses given the patient’s response to therapy and evolution of findings over time. Solitary plasmacytoma has been shown in literature to re-mineralize, and it is associated with persistently elevated alkaline phosphatase. POEMS syndrome could possibly encompass all the patient's symptoms and laboratory findings, although the patient did not present with any appreciable organomegaly to complete the traditional POEMS sequelae. Other differential diagnoses such as multiple myeloma, meningioma, schwannoma, chordoma, and nasopharyngeal carcinoma are less likely. Further workup is required to reach a definitive diagnosis.