The classification and delineation of spinal muscular atrophy (SMA) has been complex and controversial. Hitherto arthrogryposis multiplex congenita (AMC) was regarded as an exclusion criteria in SMA(1). However, recent data strongly suggests that AMC of neurogenic origin is genetically hetero-geneous with a subgroup being allelic to SMA(1).

We describe here in a non-LBW, non asphyxiated neonate brought to the referral neonatal unit, Lok Nayak hospital on the 14th day of life for respiratory distress, pooling of secretions and lower limb deformities since birth. Examination revealed tachypnea, pooling of secretions, V-shaped upper lip and tongue fasciculations. Gag reflex was absent, there was bilateral asymmetric facial nerve palsy, areflexia, hypotonia and reduced muscle bulk with preservation of the thenar and hypothenar eminences. Power in the upper limbs was restricted to movements of the digits. Lower limbs were arthrogrypotic -the hip was fixed in flexion, knees were extended, ankles were dorsi flexed and the foot had calcaneovalgus deformity. The neonate received mechanical ventilation from Day 17-21 for an intractable apnea. She was taken against medical advise on Day 28 while still oxygen dependent. The muscle biopsy changes were compatible with SMA. The cranial CT scan was non-contributory. The CPK value done on day 9 was 9.9 IU/I. Nerve conduction velocity could not be done as the neonate was not fit for transportation.

Arthrogryposis refers to a symptom complex characterized by multiple joint contractures that are present at birth ascribed to limitation of fetal movement in utero which may be the result of neuropathy, myopathy, abnormal connective tissue, in utero restraint or maternal illness like myasthenia gravis or multiple sclerosis.

The term neurogenic arthrogryposis is used to denote the association of arthrogry-posis with several conditions including infantile SMA and primary degeneration of anterior horn cells, anterior roots or peripheral nerve(2). Although SMA remains the most common cause of neurogenic arthrogryposis, arthrogryposis is unusual in newborns with SMA despite the high frequency of intrauterine hypotonia(2). This disproportion between the expected and observed suggests that neurogenic arthrogryposis in SMA is a separate genetic entity. Recently survival motor neuron(SMN) gene has been identified as the SMA determining gene. Indeed atypical forms of infantile SMA with cerebellar hypoplasia, pontocerebellar degeneration etc. could represent separate genetic entities(3). Also, Burglen et al.(1) observed that SMN gene was lacking in 6/12 patients of the SMA-AMA association which suggests that AMC of neurogenic origin is genetically hetero-geneous with a subgroup being allelic to SMA.

The AMC-SMA association needs differentiation from neurogenic arthrogry-posis due to anterior horn cell dysgenesis and congenital hypomyelinating neuropathy. In SMA, muscle biopsy on routine histochemical stains demonstrates a typical picture of denervation atrophy with groups of small fibres adjacent to groups of normal or hypertrophied fibers. This picture contrasts with the replacement of whole muscles fascicles or parts of fascicles by fat tissue seen in the non-SMA cases like anterior horn cell degeneration or dysgenesis(4).

Congenital Hypomyelinating Neuropathy is a rare potentially reversible cause of infantile neuromuscular weakness and its occurrence in association with AMC has been reported making it an important differential diagnosis. A clinical pointer in this regard is the absence of cranial nerve involvement(5). Visualization of the intramuscular nerves or a nerve biopsy will show absence of myelin, atypical onion bulbs and preservation of axons(5).

N.B. Mathur,
Jitender Nagpal,
Medha Tatke*,
R.K. Saran*,
The Referral Neonatal Unit,
Department of Pediatrics,
Maulana Azad Medical College and
*Department of Pathology,
GB Pant Hospital, New Delhi 110 002, India.
E-mail: [email protected]