Hyperammonemic encephalopathy in multiple myeloma

Non-producer multiple myeloma presenting with acute hyperammonemic encephalopathy: case report

BACKGROUND

Hyperammonemic encephalopathy (HE) is a rare and life-threatening complication of multiple myeloma, with underlying mechanisms that are not fully understood. In contrast to previously reported cases, most of which have been associated with IgG or IgA isotypes, we describe a patient with HE as the presenting symptom of non-producer multiple myeloma (NPMM).

CASE PRESENTATION

A 60-year-old man developed lethargy that progressed into coma. He was found to have an elevated ammonia level, despite normal hepatic function. He was diagnosed with HE secondary to NPMM, demonstrating 80% plasma cells without light chain expression in the bone marrow and absence of a monoclonal protein in the serum or urine, including by matrix-assisted laser desorption ionization time-of-flight mass-spectrometry (MASS-FIX). Myeloma-directed therapy with daratumumab, bortezomib, cyclophosphamide and dexamethasone successfully reversed his HE. At clinical relapse, he received salvage chemotherapy followed by venetoclax therapy, leading to a short period of neurological recovery.

CONCLUSIONS

This case demonstrates that HE can occur in a patient with NPMM and challenges the mechanism suggested by limited prior studies; i.e., that excess ammonia in multiple myeloma arises from degradation of M-proteins. We postulate that the neoplastic plasma cells in NPMM have amplified amino acid metabolism, despite lacking detectable intracellular or secreted immunoglobulins.

Hyperammonemic Encephalopathy in Multiple Myeloma: A Case Report

Multiple myeloma (MM) typically presents as lytic bony lesions, hypercalcemia, anemia, and renal failure. Only a few cases of hyperammonemic encephalopathy (HE) attributed to multiple myeloma have been reported. We report a case of a 68-year-old Hispanic female diagnosed with multiple myeloma and presented with altered mental status and elevated ammonia levels found to have HE. The pathology behind HE is associated with higher ammonia levels produced by myeloma cell lines in the absence of liver disease. Due to the wide range of differentials for altered mental status (AMS), HE often gets missed and causes delayed treatment and the associated higher mortality. The primary treatment is chemotherapy. Lactulose and rifaximin must be initiated; however, it is ineffective if solely used. In our case, chemotherapy was not considered a treatment option in light of the patient's pancytopenia and infection. Our case is unique, as despite adequately treating other commonly suspected causes of AMS such as infection, there was no expected improvement in the patient's clinical status noticed, eventually leading to intubation due to worsening AMS. Given the patient's history of multiple myeloma, non-compliance with chemotherapy before presentation, and elevated ammonia levels raised suspicion for HE. Clinicians are encouraged to acquaint themselves with HE as a differential for patients presenting with MM flare and AMS, specifically when other potential causes of AMS are ruled out and addressed.

Neurologic Complications of Lymphoma, Leukemia, and Paraproteinemias

PURPOSE OF REVIEW

This article reviews the spectrum of neurologic complications associated with lymphoma, leukemia, and paraproteinemic disorders. While leptomeningeal metastasis is the most common complication of lymphoma and leukemia and peripheral neuropathy is the most common complication of paraproteinemic disorders, clinicians need to be familiar with the diverse neurologic complications of these disorders.

RECENT FINDINGS

Lymphomatous nervous system involvement can be difficult to diagnose, especially when it is the presenting symptom. CSF cytology and flow cytometry, as well as the imaging pattern, assist in diagnosis. Neurologic complications are less common in Hodgkin lymphoma; however, some unique paraneoplastic syndromes are associated with Hodgkin lymphoma, including primary central nervous system angiitis, limbic encephalitis, and cerebellar degeneration. Recent reports suggest that anti-metabotropic glutamate receptor 5 (mGluR5) antibodies are associated with limbic encephalitis and that anti-Tr antibodies are associated with cerebellar degeneration in Hodgkin lymphoma. Polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, and skin changes (POEMS) syndrome is often misdiagnosed as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). A lambda protein, thrombocytosis, and elevated vascular endothelial growth factor (VEGF) can all be helpful clues in diagnosis. Early recognition is important, as the neuropathy responds to radiation therapy or chemotherapy.

SUMMARY

Neurologic involvement can occur throughout the disease course in lymphoma and leukemia, including at presentation, with systemic progression, and at relapse. In paraproteinemias, the peripheral neuropathy phenotype, monoclonal protein type, and associated autonomic and systemic features aid in identification of an underlying plasma cell disorder.

Multiple Myeloma-Induced Hyperammonemic Encephalopathy

Multiple myeloma (MM) typically presents with hypercalcemia, renal insufficiency, anemia, and bone lesions. Elevated ammonia level manifesting as altered mental status is a rare complication in MM. We report an interesting case of hyperammonemic encephalopathy in a 73-year-old male with advanced relapsing kappa-light chain MM.