Multifocal Motor Neuropathy Clinical features Diagnosis Differential Diagnosis Therapy Prognosis NCS Findings

1. Multifocal Motor Neuropathy
PREPARED BY:
MOHIBULLAH KAKAR, FMIC, KABUL-AFGHANISTAN 2019
REFERENCE: UPTODATE 2017

2. Multifocal motor neuropathy
Multifocal motor neuropathy (MMN), also known as multifocal motor neuropathy with
conduction block, is a rare neuropathy.
characterized by
◦ progressive asymmetric weakness
◦ atrophy without sensory abnormalities
◦ a presentation similar to that of motor neuron disease

3. PATHOGENESIS
MMN is considered an immune-mediated disorder given the following observations :
◦ Clinical improvement with intravenous Immune globulin therapy
◦ The presence of anti-GM1 antibodies in many but not all patients
◦ A perivascular lymphocytic infiltration observed on nerve biopsy in some reports
It is not clear that anti-GM1 antibodies are involved in the pathogenesis of MMN, but in 30-80%
anti-GM1 antibodies were noted in biopsy.
MMN is associated with conduction block on electrodiagnostic studies,
Segmental nerve demyelination is not considered MMN

4. PATHOGENESIS
One hypothesis is that the conduction block may be caused by an antibody-mediated attack
affecting sodium channels and other nerve components at the nodes of Ranvier.
Epidemiology:
◦ The prevalence is 0.6-2 person in 100,000
◦ Men are more effected than women
◦ Disease onset between 20 – 50 yrs, but meanly involve between 30 – 40 yrs

5. CLINICAL FEATURES
The typical clinical presentation of MMN is one of subacute onset with asymmetric weakness.
Lower motor neuron signs often present in a bibrachial pattern, producing arm and hand
weakness without associated sensory loss
The weakness usually begins as a focal mononeuropathy affecting the distal arms; wrist drop
and hand weakness are common initial symptoms.
Upper limbs involvement is twice more than lower limbs
In patients with arm onset, progression usually involves spread of the weakness to the
contralateral arm followed by the legs

6. CLINICAL FEATURES
Some patients develop fasciculations or cramps.
Muscle atrophy occurs late in the course of the disease.
Deep tendon reflexes are variably affected, being decreased in most cases but normal or brisk
(but not pathologic) in others.
Cranial nerves, bulbar muscles, and respiratory muscles are most often spared in MMN
Motor nerve conduction studies often show evidence of conduction block, representing focal
demyelination.
Sensory conduction through the same segment of nerve is normal.

7. CLINICAL FEATURES
Elevated titers of anti-GM1 antibodies may be seen in 30 to 80 percent of patients.
but it is uncertain whether these antibodies play a role in the pathogenesis of the disease.
Cerebrospinal fluid protein is normal.

8. Diagnostic criteria
Diagnostic criteria for MMN have been proposed by the European Federation of
Neurological Societies/Peripheral Nerve Society (EFNS/PNS):
the two core criteria for MMN (both must be present) are:
◦ Slowly progressive or stepwise progressive, focal, asymmetric limb weakness, that is, motor involvement
in the motor nerve distribution of at least two nerves, for more than one month. If symptoms and signs
are present only in the distribution of one nerve only a possible diagnosis can be made.
◦ No objective sensory abnormalities except for minor vibration sense abnormalities in the lower limbs

9. Diagnostic criteria
Supportive clinical criteria are as follows :
◦ Predominant upper limb involvement
◦ Decreased or absent tendon reflexes in the affected limb
◦ Absence of cranial nerve involvement
◦ Cramps and fasciculations in the affected limb
◦ Response in terms of disability or muscle strength to immunomodulatory treatment
Exclusion criteria are the following:
◦ Upper motor neuron signs / Marked bulbar involvement
◦ Sensory impairment more marked than minor vibration loss in the lower limbs
◦ Diffuse symmetric weakness during the initial weeks

10. Differential Diagnosis
Features MMN MND CIDP
IVIG Responsive - Responsive
Glucocorticoids No Response - Responsive
Plasma Exchange No Response - Responsive
Bulbar muscle Not involve Involved Involve
Cranial Nerves No Involve Involved Involve
Respiratory Muscle Not Involve/ Rarely Involved Involved
an immune-mediated
disorder
Yes No Yes
Symmetrical Asymmetry Symmetrical Symmetrical
Reflexes Absent/Decreased Hyperreflexia Areflexia
Babinski Normal + -/+ (+ poor prognosis)
CSF Normal Normal Abnormal (Protein, WBC)

11. Treatment
This recommendation is consistent with current guidelines from the European Federation of
Neurological Societies/Peripheral Nerve Society and the American Academy of Neurology:
◦ IVIG, 2 g/kg, given over two to five days, for initial treatment of patients with MMN who require
treatment due to disease progression or disability.
◦ Our preferred regimen is 0.4 g/kg daily for five consecutive days

12. PROGNOSIS
The prognosis of MMN is one of slow progression of disease and disability in untreated patients
Spontaneous remission has not been reported.
In patients with very slow progression and minimal disability, immunomodulatory treatment
may be deferred so as to avoid the risk of side effects.
However, treatment should begin early in the disease if activities of living are impaired