The first step of the topical diagnostics algorithm
Solving a neurological clinical case begins with differentiating the level of the lesion: central nervous system (CNS) or peripheral nervous system (PNS). This step sets the direction for further localization of the lesion and accounts for up to 80–90% of a correct exam answer.
Two clinical criteria serve as reference points for differentiation:
- the character of the paresis (central or peripheral);
- the type of sensory disturbance.
Central and Peripheral Paresis
A CNS lesion occurs via the pyramidal tract and is therefore accompanied by signs of disinhibition of spinal reflex arcs. A PNS lesion deprives the muscle of the nerve's trophic and tonic influence, leading to rapid denervation atrophy.
Signs of central paresis:
- increased muscle tone of a spastic type;
- exaggeration of deep tendon and periosteal reflexes;
- expansion of reflexogenic zones;
- appearance of pathological reflexes — Babinski, Rossolimo, Tromner;
- absence of rapid atrophy and fasciculations.
Signs of peripheral paresis:
- decreased muscle tone (hypotonia or atonia) due to impairment of extrapyramidal and segmental influences;
- diminution or loss of reflexes;
- rapidly developing muscle atrophy;
- fasciculations — indicating a lesion of the anterior horns of the spinal cord or the motor neuron.
Sensory Disorders in PNS Lesions
At the peripheral nervous system level, several typical distribution patterns of sensory disturbances are distinguished.
- Mononeuropathy is damage to a single nerve. In clinical case studies, the radial, ulnar, median, and fibular nerves are most frequently featured. It is accompanied by motor phenomena: "wrist drop" (radial), "claw hand" (ulnar), "ape hand" with the inability to oppose the thumb (median), steppage gait (fibular).
- Polyneuropathy — symmetric distal involvement of multiple nerves. A reference feature in the clinical case is sensory disturbance in a "stocking and glove" distribution. A classic example is diabetic polyneuropathy.
- Radicular type — disorders spread in a longitudinal band ("lampassstripe"), accompanied by shooting pains and peripheral paresis of the indicator muscles of the corresponding nerve root.
Sensory Disorders in CNS Lesions
Within the CNS, three main types of sensory disturbance distribution are distinguished.
- Segmental-dissociated type — isolated loss of superficial (pain and temperature) sensation with preserved deep sensation. Distributed in a "jacket" or "half-jacket" pattern. Characteristic of syringomyelia and lesions of the posterior horns of the spinal cord.
- Spinal tract type — loss of sensation below a specific level (e.g., "from the level of the umbilicus", "from the level of the inguinal crease"). Indicates a lesion of the spinal cord pathways.
- Cerebral tract type — involvement of sensory pathways above the spinal cord.
Variants of the Cerebral Tract Type
Within the cerebral tract variant, two clinically important forms are distinguished.
- Alternating syndromes — sensory or motor disturbances on the face on one side combined with tract-type disorders on the opposite half of the body. Indicate a brainstem lesion, where the pathway decussation and cranial nerve nuclei are located at different levels.
- Brachiofacial type — the lesion involves the face and arm (or the face, arm, and leg) on one side. Indicates a lesion of the cerebral hemisphere, most often in the area of the internal capsule or cortex.
Logic of Clinical Case Analysis
When analyzing a neurological clinical case, it is advisable to proceed sequentially:
- Evaluate the character of the paresis — determine whether it is central or peripheral, based on tone, reflexes, pathological signs, and the presence of atrophy and fasciculations.
- Analyze the distribution of sensory disturbances and compare it with typical patterns (mono-, poly-, radicular, segmental-dissociated, spinal tract, cerebral tract).
- Conclude on the level of the lesion: peripheral nerve, nerve root, spinal cord, brainstem, or hemisphere.
This sequence allows narrowing down the topical diagnosis to a specific anatomical structure even before analyzing additional syndromes.
Key points
- The first step of topical diagnostics is to distinguish a CNS lesion from a PNS lesion.
- Central paresis: hypertonia, hyperreflexia, expansion of reflexogenic zones, pathological signs (Babinski, Rossolimo, Tromner).
- Peripheral paresis: hypotonia, hyporeflexia, rapid atrophy, fasciculations (a sign of anterior horn involvement).
- "Stockings and gloves" — a marker of polyneuropathy; longitudinal "lampass stripe" with shooting pain — radicular syndrome.
- Segmental-dissociated type ("jacket", "half-jacket") is characteristic of syringomyelia.
- Spinal tract disorders have a clear horizontal level of sensory loss.
- Alternating syndromes indicate a brainstem lesion, while the brachiofacial type indicates a hemispheric lesion.
- Topical diagnosis is built sequentially: type of paresis → type of sensory disturbances → level of the lesion.