Simian hand deformity

Introduction In the late stage of iliac muscle atrophy, the interosseous muscle appears in the hand, and the large and small intermuscular muscles atrophy, forming a deformity of the hand. Peronial myoatrophy, also known as Charcot-Marie-Tooth disease (CMT), is the most common group of peripheral neuropathies, accounting for approximately 90% of all hereditary neuropathies. The common features of this group of diseases are the onset of children or adolescents, chronic progressive sacral muscle atrophy, and the symptoms and signs are relatively symmetrical. Most patients have a family history. Because of the main clinical features of iliac muscle atrophy, it is also known as peroneal myoatrophy. According to neurophysiological and neuropathological findings, CMT is classified into type I and type II, CMTI type is called hypertrophic type, and type CMTII is called neuronal type.

Cause

The cause of the "hand rub" deformity

(1) Causes of the disease

The disease is mainly caused by genetic factors, CMT1 type, CMT2 type are autosomal dominant inheritance, there may be scattered cases.

The pathogenic gene of 1CMT1A is located at 17p11.2-12, and the nuclear gene encodes peripheral neuromyelin protein 22 (PMP22). Repeated mutation of PMP22 gene leads to overexpression, which increases PMP22 protein. A small number of patients produce abnormal PMP22 protein due to PMP22 gene mutation. And cause illness;

2CMT2 type: CMT2A gene is located on chromosome 1p35-36, CMT2B is located at 3q13-22, CMT2C is located at 5q, CMT2D is located at 7p14, and CMT2E is located at 8p21. CMT also has an X-linked dominant (CMTX) chromosomal recessive (CMT4) approach.

(two) pathogenesis

Genetic mode

(1) CMTI type: it can be autosomal dominant, recessive and X-linked dominant or recessive. Recent studies have shown that CMTI types are divided into IA type, IB type and IC type. The most common type of CMTIA (56% to 60%) is caused by mutation of the PMP-22 gene on autosomal 17P11.2-12. The CMTIB type is rare (30%), and the pathological gene is involved in Iq21-23, which is associated with mutation of the myelin protein P0 (MPZ) gene. The pathological genes of the IC type are still unknown. The X-linked pathological gene is at Xq13-1.

(2) CMTII type: There are three types of inheritance, usually autosomal dominant, recessive and X-linked inheritance. The disease often stains the dominant pathological gene at Ip35-36. Changyin and X-linked pathological genes are unknown.

2. Pathological changes

(1) CMTI type: The results of CMTI-type sural nerve biopsy showed that the number of major large and medium-diameter fibers was significantly reduced, and collagen in the bundle was proliferated. With age, the density of myelinated fibers is progressively reduced, and demyelination is aggravated. Due to the enhanced segmental demyelination and remyelination process, Schwann cell proliferation and neuroendosome components form a concentric "onion ball"-like structure around the axon. Spinal cord degeneration, in which the thin bundle is more pronounced than the wedge bundle.

(2) CMT type II: CMT type II sural nerve pathology is mainly axonal degeneration, demyelinating is not significant, Schwann cell proliferation is "onion ball" change and rare.

an examination

Related inspection

Bone and joint MRI

"hands" deformity check

Clinical manifestation

Often in children or adolescent insidious onset. More men than women, progress is slow. In most patients, muscle atrophy and muscle weakness begin from the distal muscles of the lower extremities (sacral muscles, total toe muscles, and small muscles of the feet), gradually developing upwards and being symmetrical. A small number of patients can also start from the hand. Muscle atrophy often has obvious boundaries, and the lower limbs do not exceed the lower third of the thigh, which resembles an "inverted bottle" (called "tiger leg"). Due to muscle atrophy, arched foot, foot drop and horseshoe varus deformity may occur, but the muscle strength is still relatively good, and is not proportional to muscle atrophy. Upper limb muscle atrophy begins with small muscles in the hand, but usually does not exceed the lower third of the forearm. The quadriplegia reflexes weakened or disappeared, and the Achilles tendon reflexes disappeared more often. There may be four limb-type sensory disturbances, accompanied by autonomic dysfunction such as rough skin, cold extremities, less sweat or cyanosis, and occasional changes in optic atrophy, retinal degeneration and nystagmus. The above clinical manifestations are often typical CMTI patients. Patients with autosomal recessive inheritance may be associated with changes in ataxia and scoliosis.

Electrophysiological examination showed that fibrillation waves and positive sharp waves and action potentials were prolonged, and the motor conduction velocity was significantly slowed down, which could be as low as 10-20 m/s, and the sensory conduction velocity was also slowed down, especially for sural nerve involvement. .

Roussy-Lévy syndrome was first reported by Roussy and Lévy in 1926. Its clinical features are similar to Friedreich's ataxia and CMT. Infancy or post-natal morbidity, first involving the lower extremities, manifests as mild distal weakness, and gradually affects the upper limbs. . Sensory disturbances are more severely damaged by positional and vibratory sensations, often accompanied by significant sensory ataxia, without cerebellar signs. Distal muscle atrophy of the extremities, high arch of the foot, posterior kyphosis of the spine, and paralysis of the tendon disappeared. Electrophysiological examination showed a slowing of nerve conduction velocity. The biopsy pathology is consistent with changes in demyelinating peripheral neuropathy. The disease is benign and can still walk at the age of 70.

Roussy-Lévy syndrome has long been classified as a spinal cerebellar degenerative disease. In recent years, molecular biology studies have shown that this disease is identical to the CMTI type gene defect, both located at 17p11.2. Combined with electrophysiological changes and pathological features of peripheral nerve biopsy, it is now clear that Roussy-Lévy syndrome should be classified as demyelinating CMT, ie CMTI type.

The genetic characteristics and clinical manifestations of CMT type II and CMTI type are very similar, but the age of onset of autosomal dominant CMT type 2 is later, with an average age of 25 years. Compared with the CMTI type, the incidence of CMT2 is low (about 1/3 of CMTI type), the sensory symptoms are relatively mild, the upper limbs are rarely affected, the peripheral nerves are not thick, the arched feet are rare, and the disease progresses relatively slowly. There is a platform period. Electrophysiological examination showed that the motor conduction velocity was normal or only slightly slowed down, and it was not less than 38-40 m/s.

Differential diagnosis

diagnosis

The diagnosis of hereditary motor sensation peripheral neuropathy mainly depends on genetic family history, clinical features, neurophysiological examination and nerve biopsy. Molecular genetic analysis can also be used for diagnosis where conditions are available.

Chronic motor sensory neuropathy in children or adolescents should consider the possibility of this disease, according to the onset of adolescent insidious, progressive lower extremity muscle atrophy, and a special distribution form (limited to the lower third of the thigh, presented "Crane legs"), but the muscle strength is relatively good, the tendon reflex often weakens or disappears, the sleeve type sensory disturbance and other characteristics, the diagnosis is not difficult, a positive family history can help diagnose.

The diagnostic points of CMT 1 and CMT 2 are as follows:

1, CMT type 1

1 within 10 years of age, chronic progressive disease, severity; peripheral symmetry progressive degeneration caused by distal muscle weakness and muscle atrophy, self-sufficient and lower limbs, CX varus clubfoot and claw-foot deformity, From months to years, the hand and forearm muscles are accompanied by or without sensory loss; often with scoliosis and foot, which is a cross-threshold gait; the course is slow and the course is stable for a long period of time; some patients have genetic mutations, but some patients have genetic mutations There is no muscle weakness and muscle atrophy, only the arched foot or nerve conduction velocity is slowed down, even without clinical symptoms.

2 check the lower leg and the lower third of the thigh muscle atrophy, shaped like a "crane leg", or inverted champagne bottle shape, hand muscle atrophy into a claw-shaped design, can affect the forearm muscle, affected limbs sputum reflexes reduced or disappear; deep and shallow feeling Reduced in gloves, socks-like distribution, with autonomic dysfunction and nutritional disorders, about 50% of cases can reach the nerve thickening, the brain is usually not tired.

3 exercise NCV slowed down to 38m / s (normal 50m / s); CSF protein normal or slightly increased; muscle biopsy showed neurogenic muscle atrophy, nerve biopsy showed peripheral nerve demyelination and Schwann cell proliferation formed "onion head "like structure.

2, CMT 2 type

1 Late onset, muscle atrophy begins in adulthood, and the symptoms and appearance are similar to CMT type 1 and to a lesser extent.

2 The NCV of exercise is normal or close to normal, and the CSF protein is normal or slightly elevated. The nerve biopsy is mainly axonal.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.