Clinical diagnosis
Case 237
【Progress】
He is scheduled to check the state of disorder of opening mouth. The distance of opening of the mouth is widening from 8mm to 15mm.
【Discussion】
As muscles of mastication, temporal muscle, masseter muscle, lateral pterygoid muscle and medial pterygoid muscle are listed. Of these, we can touch temporal muscle and masseter muscle but not lateral & pterygoid muscles. Master muscle exists at the surface of the mandibular bone while temporary muscles enter the inside of mandibular bone. Lateral & medial pterygoid muscles exist inside the mandibular bone, thus, unable to be palpable and visible. Coordination of these muscles is necessary to open, close and chew our mouth.
Lateral pterygoid muscle composes of superior part and inferior part, while medial pterygoid muscle composes of superficial part and deep part. The function of lateral pterygoid muscle works when we open the mouth: it functions when we pronounce ‘La or Ah in Japanese’. The function of medial pterygoid muscle works when we close our mouth: it functions when we pronounce ‘Me or Ih in Japanese’.
Muscles of mastication are innervated of trigeminal nerve. Trigeminal nerve is Vth cranial nerve and divided into three main branches of ophthalmic (V1), maxillary (V2) and mandibular (V3). Most nerve branches are basically sensory. Several subbranches of V3 are motor and innervate several muscles including four muscles of mastication.
Unilateral atrophy of masticatory muscles is rare. Etiology factors are supposed to be viral infection, tick infection, trauma, stroke, tumor, Sjogren syndrome and unknown (1-9). Typical symptoms are asymmetry of the face, wasting and weak of the masticatory muscles and the painful of the healthy masticatory muscle due to over working or compensatory hypertrophy. There was one report case with focal atrophy of masticatory muscles due to infection of Borrelia burgdorferi called Raimubyou in Japanese (1).
The main symptom of our case is the disorder of opening mouth and right-sided pain of masticatory muscle. Gd-enhanced MRI and contrast-enhanced CT showed no evidence of tumor but hypertrophy of right masticatory muscles and atrophy of left masticatory muscle. At first, we diagnosed inflammatory myositis of right masticatory muscle incorrectly. Then, we reached final diagnosis of atrophy of left masticatory muscles. Further in details, it was found that atrophy of left temporal muscle, superior head of left lateral pterygoid muscle and deep head of left medial pterygoid muscle. Although the cause of unilateral atrophy of masticatory muscle in our case, is unknown, the etiology is warranted to be investigated.
【Summary】
We presented a sixty five-year-old male suffering from disorder of opening mouth and painful right masticatory muscles. MRI & CT showed hypertrophy of right masticatory muscles and focal atrophy of left masticatory muscles; left temporary muscle and lateral & medial pterygoid muscles. In details, focal atrophy of superior head of lateral pterygoid muscle, deep head of medial pterygoid muscle and temporal muscle. It is borne in mind that temporal muscle and lateral & medial pterygoid muscles exist inside the mandibular bone. Lateral pterygoid muscle works when we pronounce ‘La’, namely in opening mouth. Meanwhile, medial pterygoid muscle works when we pronounce ‘Me’ in closing mouth. The masticatory muscles are innervated of trigeminal nerve branch (V3). The etiology of focal unilateral atrophy is viral infection, tick infection, tumor, trauma und unknown.
【References】
1.Kamppi A, et al. Focal atrophy of the unilateral masticatory muscles caused by pure trigeminal motor neuropathy: case report. 2018; 6: 939-943
2.Kang, Y.K,et al. Pure trigeminal motor neuropathy: a case report. Arch. Phys. Med. Rehabil. 2000: 81: 995– 998.
3.Tsugawa, JS, et al. Pure trigeminal motor neuropathy with an antecedent infection: a case report. Rinsho Shinkeigaku (Clin. Neurol.) 2014; 54: 515– 517. Article in Japanese.
4.Park, KS, et al. Unilateral trigeminal mandibular motor neuropathy caused by tumor in the foramen ovale. J. Clin. Neurol. 2006; 2: 194– 197.
5.Ko, KF, et al. A case of isolated pure trigeminal motor neuropathy. Clin. Neurol. Neurosurg. 1995; 97: 199– 200.
6.Wilson, MH, et al. Focal atrophy of the masticatory muscles caused by pure trigeminal motor neuropathy: case report. Br. J. Oral Maxillofac. Surg. 2016; 54: e13– e14.
7.Andonopoulos, AP, et al. The spectrum of neurological involvement in Sjögren's syndrome. Br. J. Rheumatol. 1990; 29: 21– 23.
8.Chiba, SY, et al. A case of pure trigeminal motor neuropathy. Rinsho Shinkeigaku (Clin. Neurol.) 1990; 30: 883– 887. In Japanese.
9.Takamatsu, KT et al.. A case of pure trigeminal motor neuropathy. Rinsho Shinkeigaku (Clin. Neurol.) 1993; 33: 541– 545. Article in Japanese.
2021.7.9