Masticatory Muscle Atrophy - Unilateral

Masticatory muscle atrophy is a symptom of masticatory muscle myositis (MMM), an inflammatory disease that affects the muscles used for chewing in dogs - in this case, it is bilateral. More information can be found at our page on this topic. Unilateral masticatory muscle atrophy can occassionally be caused by MMM but most commonly represents an underlying disorder of the motor branch of the trigeminal nerve (Cranial nerve V).

Clinical findings and outcome of dogs with unilateral masticatory muscle atrophy

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The aim of this study was to evaluate the clinical presentation, magnetic resonance imaging (MRI) findings, and outcome of dogs with unilateral MM atrophy.

Presumptive trigeminal nerve sheath tumor (pTNST) was diagnosed in 30 of the 63 dogs evaluated (47.6%); survival time varied from 1 day to 21 months (median, 5 months). Other extra‐axial mass lesions were observed in 13 dogs (20.6%); survival time varied from 6 days to 25 months (median, 2.5 months). In 18 dogs (28.6%), no abnormalities were observed on MRI; neurological signs only progressed in 1 dog. Dogs with mass lesions were more likely to be euthanized or experience neurological deterioration, whereas these outcomes occurred less often in dogs in which no causative lesion could be identified.

Treatment of MRI-Diagnosed Trigeminal Peripheral Nerve Sheath Tumors by Stereotactic Radiotherapy (SRT) in Dogs

The aim of this study was to assess the outcome of dogs with suspected intracranial trigeminal nerve peripheral nerve sheath tumors (PNST) treated with SRT.

SRT was delivered in 3 dose fractions of 8 Gray (Gy) on consecutive days or every other day to a total dose of 24 Gy.

Median disease-specific survival was 745 days (range: 99–1375 days, n = 6). No signs of acute adverse effects of radiation treatment were recorded. Late radiation effects versus tumor progression could not be confirmed histopathologically because of the few animals undergoing necropsy.