Inherited neurological disorders - hereditary spastic paresis

Description

Hereditary spastic paraplegia (HSP) - a genetically heterogeneous group of disorders causing progressive spasticity and weakness predominantly of the lower limbs, from length-dependent degeneration of the corticospinal tract axons

Highly genetically heterogeneous (over 80 causative genes identified, inherited as autosomal dominant, recessive, or X-linked depending on the specific gene) - autosomal dominant SPAST (SPG4)-related HSP is the most common single cause overall

The longest corticospinal tract axons (supplying the lower limbs) are affected preferentially - a "dying-back" axonopathy pattern, explaining why lower limb spasticity typically predominates over upper limb or bulbar involvement, especially early in the disease course

Classified as "pure" HSP (spasticity/weakness only, typically the SPAST/SPG4 pattern) or "complicated" HSP (spasticity plus additional features - ataxia, cognitive impairment, peripheral neuropathy, optic atrophy - depending on the specific causative gene)
Progressive, symmetric lower limb spasticity with hyperreflexia and extensor plantar responses, but relatively preserved power early in the disease course, distinguishes it clinically from a predominantly weakness-driven neuromuscular disorder
Genetic testing (gene panel, given the marked genetic heterogeneity) confirms the specific subtype and informs inheritance pattern/family counselling

No disease-modifying treatment currently exists - management is symptomatic: spasticity management (physiotherapy, oral antispasmodics such as baclofen, botulinum toxin for focal spasticity), mobility aids, and management of any complicating features in the "complicated" subtypes
Genetic counselling given the variable inheritance patterns across the different causative genes

Hereditary neuropathies (Charcot-Marie-Tooth, a different but sometimes overlapping differential), primary lateral sclerosis (a related but distinct upper motor neuron disorder), cerebral palsy (an important non-genetic mimic/differential, particularly when there is no family history)

Pure HSP typically has a normal life expectancy with slowly progressive disability over decades; complicated forms have more variable prognosis depending on the additional features present

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