DiagnosticTree/UlnarForearm
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{
"model": "bayesian_lr_scoring",
"version": "1.0",
"region_label": "Ulnar Forearm Pain",
"description": "Probabilistic scoring model for pain along the ulnar (little-finger side) forearm. None of the four sources lies in the forearm itself - all refer to the ulnar forearm from the trunk and shoulder girdle. Latissimus dorsi carries pain from the mid-back down the posterior arm to the ulnar hand; pectoralis major and minor refer from the front of the chest down the ulnar arm to the last two or three fingers (the left pectoralis major pattern mimics cardiac pain); and serratus posterior superior refers a deep under-the-scapula ache down to the ulnar forearm and little finger. Structural differential led by ulnar nerve entrapment at the cubital tunnel and Guyon's canal, with medial epicondylitis, C8-T1 radiculopathy, thoracic outlet syndrome, and the hook-of-hamate / ulnar artery lesions (Davis & Kane; Lleva 2025; Hsu/Otoshi; Sanderson 2020; Shehab & Mirabelli 2013).",
"thresholds": {
"early_exit_posterior": 0.55,
"early_exit_gap": 0.18,
"pairwise_trigger": 0.15
},
"muscles": {
"latissimus_dorsi": {
"label": "Latissimus Dorsi",
"prior": 0.25,
"page": "Muscle:Latissimus_Dorsi",
"key_trp_note": "Refers from the inferior scapular angle and mid-back down the posterior arm to the ulnar forearm and hand, including the ring and little fingers. The mid-thoracic ache is characteristically constant and not changed by ordinary movement, which is itself a clue. One of the four pseudo-thoracic-outlet muscles (with pectoralis major, teres major, and subscapularis). Suspect it when ulnar-forearm pain is accompanied by mid-back or posterior axillary-fold pain; activated by sustained loaded reaching (pulling, working overhead).",
"subtitle": "Mid-back and inferior scapular pain spilling down the back of the arm to the ULNAR forearm and hand (ring and little fingers); a constant mid-back ache unaffected by movement; a member of the pseudo-thoracic-outlet group"
},
"pectoralis_major": {
"label": "Pectoralis Major",
"prior": 0.25,
"page": "Muscle:Pectoralis_Major",
"key_trp_note": "The sternal section refers from the anterior chest down the medial arm and volar forearm to the ulnar hand, including the last two to two-and-a-half digits. CRITICAL: the left-sided sternal pattern mimics angina/myocardial ischaemia in exact detail, and relief of the pain by trigger-point treatment does NOT exclude cardiac disease - the two coexist and cardiac status must be established independently. Driven by round-shouldered posture; the subclavius and pectoralis minor are almost always co-active.",
"subtitle": "Anterior chest pain extending down the inner arm and forearm to the ULNAR hand and last two to three fingers; the LEFT sternal pattern mimics cardiac pain - relief by trigger-point treatment does NOT exclude heart disease"
},
"pectoralis_minor": {
"label": "Pectoralis Minor",
"prior": 0.25,
"page": "Muscle:Pectoralis_Minor",
"key_trp_note": "A deep anterior chest muscle whose pain spills along the ulnar arm, elbow, forearm, and hand to the last three fingers, closely mimicking the pectoralis major pattern and also able to mimic cardiac pain. Its taut fibres can entrap the brachial plexus medial cord, producing 4th/5th digit numbness and paraesthesia - a true myofascial thoracic-outlet mechanism. Almost never found active without pectoralis major; examine and treat the two together.",
"subtitle": "Front-of-chest / anterior deltoid pain spilling down the ULNAR arm and forearm to the last three fingers; can compress the brachial plexus (4th/5th finger numbness); almost never active without pectoralis major"
},
"serratus_posterior_superior": {
"label": "Serratus Posterior Superior",
"prior": 0.25,
"page": "Muscle:Serratus_Posterior",
"key_trp_note": "A thin respiratory muscle beneath the scapula. Its essential ache is felt DEEP under the upper scapula - the patient reaches back but cannot touch it because the scapula covers the spot - and spills down the posterior arm and triceps to the ulnar forearm, hand, and all of the little finger, often with referred C8-T1 numbness that is referred sensation rather than a true deficit. This makes it the single most common myofascial mimic of C8-T1 radiculopathy. Activated by respiratory overload (coughing, pneumonia, asthma) and by reaching forward; the scapula must be abducted to reach the trigger point. Always examine the neck for scalene trigger points, which drive it as satellites.",
"subtitle": "A deep ache UNDER the shoulder blade that the patient cannot reach, spreading down the back of the arm to the ULNAR forearm, hand, and the whole little finger, often with referred numbness; brought on by coughing or a chest illness; the commonest myofascial mimic of a pinched C8 nerve"
}
},
"questions": [
{
"id": "q_zone",
"text": "Where does the pain seem to come from?",
"sublabel": "The dominant origin of the whole pattern",
"type": "choice",
"answers": [
{
"id": "mid_back",
"label": "The MID-BACK or below the shoulder blade, wrapping down the arm",
"sublabel": "Posterior thorax source",
"lr": {
"latissimus_dorsi": 6.5,
"pectoralis_major": 0.5,
"pectoralis_minor": 0.5,
"serratus_posterior_superior": 1.5
}
},
{
"id": "front_chest",
"label": "The FRONT of the chest, extending down the inner arm",
"sublabel": "Anterior chest source",
"lr": {
"latissimus_dorsi": 0.4,
"pectoralis_major": 6.0,
"pectoralis_minor": 3.5,
"serratus_posterior_superior": 0.5
}
},
{
"id": "front_shoulder_chest",
"label": "The FRONT of the shoulder / upper chest, spilling down the arm",
"sublabel": "Anterior shoulder-chest source",
"lr": {
"latissimus_dorsi": 0.5,
"pectoralis_major": 2.5,
"pectoralis_minor": 6.0,
"serratus_posterior_superior": 0.6
}
},
{
"id": "under_scapula",
"label": "DEEP under the shoulder blade, in a spot I cannot quite reach",
"sublabel": "Sub-scapular source",
"lr": {
"latissimus_dorsi": 1.2,
"pectoralis_major": 0.5,
"pectoralis_minor": 0.5,
"serratus_posterior_superior": 7.0
}
}
]
},
{
"id": "q_distal",
"text": "Which fingers does the pain or numbness reach?",
"sublabel": "The ulnar fingers reached help separate the sources",
"type": "choice",
"answers": [
{
"id": "ring_little",
"label": "The RING and LITTLE fingers",
"sublabel": "Ring & little (4th/5th)",
"lr": {
"latissimus_dorsi": 3.0,
"pectoralis_major": 1.5,
"pectoralis_minor": 2.0,
"serratus_posterior_superior": 1.5
}
},
{
"id": "last_three",
"label": "The last THREE fingers (middle, ring, little) / ulnar hand broadly",
"sublabel": "Last three fingers",
"lr": {
"latissimus_dorsi": 1.0,
"pectoralis_major": 2.5,
"pectoralis_minor": 3.0,
"serratus_posterior_superior": 0.8
}
},
{
"id": "whole_little",
"label": "ALL of the LITTLE finger especially, down the ulnar edge",
"sublabel": "Whole little finger / ulnar edge",
"lr": {
"latissimus_dorsi": 1.2,
"pectoralis_major": 0.8,
"pectoralis_minor": 1.0,
"serratus_posterior_superior": 4.0
}
},
{
"id": "no_fingers",
"label": "It stays in the arm/forearm - no clear spread into the fingers",
"sublabel": "No finger spread",
"lr": {
"latissimus_dorsi": 1.5,
"pectoralis_major": 1.0,
"pectoralis_minor": 0.8,
"serratus_posterior_superior": 1.2
}
}
]
},
{
"id": "q_provocation",
"text": "Which activity most reliably brings on the pain?",
"sublabel": "Choose the single strongest aggravator",
"type": "choice",
"answers": [
{
"id": "loaded_reaching",
"label": "Sustained loaded reaching, pulling, or working overhead",
"sublabel": "Loaded reaching / pulling",
"lr": {
"latissimus_dorsi": 6.0,
"pectoralis_major": 1.0,
"pectoralis_minor": 1.0,
"serratus_posterior_superior": 1.5
}
},
{
"id": "round_shoulder_posture",
"label": "Round-shouldered posture, or reaching/lifting forward across the chest",
"sublabel": "Round-shoulder / anterior load",
"lr": {
"latissimus_dorsi": 0.7,
"pectoralis_major": 5.0,
"pectoralis_minor": 5.0,
"serratus_posterior_superior": 0.8
}
},
{
"id": "cough_breathing",
"label": "Coughing, deep breathing, or after a chest illness (pneumonia, asthma, bronchitis)",
"sublabel": "Respiratory overload",
"lr": {
"latissimus_dorsi": 0.6,
"pectoralis_major": 0.8,
"pectoralis_minor": 1.2,
"serratus_posterior_superior": 7.0
}
},
{
"id": "nonspecific",
"label": "No clear movement trigger - a constant ache regardless of activity",
"sublabel": "Constant / non-specific",
"lr": {
"latissimus_dorsi": 3.0,
"pectoralis_major": 1.0,
"pectoralis_minor": 0.8,
"serratus_posterior_superior": 1.5
}
}
]
},
{
"id": "q_chest_cardiac",
"text": "Is there anterior chest pain, or a pressure/constriction in the chest (especially left-sided) with the arm pain?",
"sublabel": "Pectoral source screen. IMPORTANT: a left-sided chest-and-ulnar-arm pattern can mimic cardiac pain - relief by trigger-point treatment does NOT exclude heart disease; establish cardiac status independently.",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes - anterior chest pain or constriction accompanies the arm pain",
"lr": {
"latissimus_dorsi": 0.5,
"pectoralis_major": 6.0,
"pectoralis_minor": 4.5,
"serratus_posterior_superior": 0.5
}
},
{
"id": "no",
"label": "No - no chest pain or constriction",
"lr": {
"latissimus_dorsi": 1.4,
"pectoralis_major": 0.3,
"pectoralis_minor": 0.4,
"serratus_posterior_superior": 1.4
}
}
]
},
{
"id": "q_under_scapula",
"text": "Is there a deep ache UNDER the shoulder blade that you reach for but cannot quite touch because the shoulder blade covers it?",
"sublabel": "Serratus posterior superior signature - the essential ache lies beneath the scapula and is only reachable when the scapula is drawn forward",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes - a deep spot under the shoulder blade I cannot reach",
"lr": {
"latissimus_dorsi": 1.2,
"pectoralis_major": 0.5,
"pectoralis_minor": 0.5,
"serratus_posterior_superior": 6.5
}
},
{
"id": "no",
"label": "No - the pain is not under the shoulder blade",
"lr": {
"latissimus_dorsi": 1.05,
"pectoralis_major": 1.1,
"pectoralis_minor": 1.1,
"serratus_posterior_superior": 0.3
}
}
]
},
{
"id": "q_medial_cord",
"text": "Is there numbness or tingling of the last fingers along with the pain?",
"sublabel": "Both pectoralis minor (medial-cord entrapment) and serratus posterior superior (referred C8-T1 sensation) can add ulnar-finger numbness; pure latissimus/pec-major referral usually does not",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes - numbness/tingling in the ulnar fingers as well as pain",
"lr": {
"latissimus_dorsi": 0.8,
"pectoralis_major": 0.9,
"pectoralis_minor": 3.0,
"serratus_posterior_superior": 2.5
}
},
{
"id": "no",
"label": "No - aching pain only, no numbness or tingling",
"lr": {
"latissimus_dorsi": 1.3,
"pectoralis_major": 1.2,
"pectoralis_minor": 0.6,
"serratus_posterior_superior": 0.7
}
}
]
},
{
"id": "q_palpation",
"text": "Where does firm palpation most precisely reproduce the familiar arm pain?",
"sublabel": "The reproducing tender point - the most specific localiser",
"type": "choice",
"answers": [
{
"id": "posterior_axillary_fold",
"label": "In the back wall of the armpit / side of the back (latissimus dorsi)",
"sublabel": "Latissimus dorsi location",
"lr": {
"latissimus_dorsi": 7.0,
"pectoralis_major": 0.5,
"pectoralis_minor": 0.5,
"serratus_posterior_superior": 0.6
}
},
{
"id": "anterior_chest_pincer",
"label": "In the chest muscle, pinched at the front of the armpit fold",
"sublabel": "Pectoralis major location",
"lr": {
"latissimus_dorsi": 0.5,
"pectoralis_major": 7.0,
"pectoralis_minor": 1.5,
"serratus_posterior_superior": 0.5
}
},
{
"id": "deep_under_pec",
"label": "Deep under the chest muscle toward the coracoid (front of shoulder)",
"sublabel": "Pectoralis minor location",
"lr": {
"latissimus_dorsi": 0.5,
"pectoralis_major": 1.5,
"pectoralis_minor": 7.0,
"serratus_posterior_superior": 0.5
}
},
{
"id": "under_scapula_rib",
"label": "Deep beneath the upper shoulder blade against the ribs (with the shoulder blade drawn forward)",
"sublabel": "Serratus posterior superior location",
"lr": {
"latissimus_dorsi": 0.8,
"pectoralis_major": 0.5,
"pectoralis_minor": 0.5,
"serratus_posterior_superior": 7.0
}
}
]
}
],
"pairwise": [
{
"id": "pw_pmaj_pmin",
"pair": [
"pectoralis_major",
"pectoralis_minor"
],
"text": "Tiebreaker - Pectoralis Major vs Pectoralis Minor",
"question": "Is the tender point superficial in the chest muscle / front of the armpit fold, or deeper toward the coracoid at the front of the shoulder (with ulnar-finger numbness)?",
"sublabel": "Both refer to the ulnar fingers and coexist; pec minor adds medial-cord numbness",
"answers": [
{
"id": "superficial",
"label": "Superficial chest muscle / axillary fold - pectoralis major",
"lr": {
"pectoralis_major": 5.0,
"pectoralis_minor": 0.5
}
},
{
"id": "deep",
"label": "Deep toward the coracoid, with ulnar-finger numbness - pectoralis minor",
"lr": {
"pectoralis_major": 0.5,
"pectoralis_minor": 5.0
}
}
]
},
{
"id": "pw_latd_sps",
"pair": [
"latissimus_dorsi",
"serratus_posterior_superior"
],
"text": "Tiebreaker - Latissimus Dorsi vs Serratus Posterior Superior",
"question": "Is the back pain a broad mid-back ache in the posterior axillary fold (latissimus), or a deep spot UNDER the shoulder blade you cannot reach, worse with coughing (serratus posterior superior)?",
"sublabel": "Both are posterior-thorax sources reaching the ulnar hand",
"answers": [
{
"id": "latd",
"label": "Broad mid-back / posterior axillary fold - latissimus dorsi",
"lr": {
"latissimus_dorsi": 5.5,
"serratus_posterior_superior": 0.4
}
},
{
"id": "sps",
"label": "Deep under-scapula spot, worse coughing - serratus posterior superior",
"lr": {
"latissimus_dorsi": 0.4,
"serratus_posterior_superior": 5.5
}
}
]
},
{
"id": "pw_latd_pmaj",
"pair": [
"latissimus_dorsi",
"pectoralis_major"
],
"text": "Tiebreaker - Latissimus Dorsi vs Pectoralis Major",
"question": "Does the ulnar arm pain come from the MID-BACK (posterior), or from the FRONT of the CHEST (with chest pain or constriction)?",
"sublabel": "Posterior thorax source vs anterior chest source - both reach the ulnar hand",
"answers": [
{
"id": "latd",
"label": "Mid-back / posterior - latissimus dorsi",
"lr": {
"latissimus_dorsi": 5.5,
"pectoralis_major": 0.4
}
},
{
"id": "pmaj",
"label": "Front of chest, chest pain/constriction - pectoralis major",
"lr": {
"latissimus_dorsi": 0.4,
"pectoralis_major": 5.5
}
}
]
},
{
"id": "pw_pmin_sps",
"pair": [
"pectoralis_minor",
"serratus_posterior_superior"
],
"text": "Tiebreaker - Pectoralis Minor vs Serratus Posterior Superior",
"question": "Is the ulnar-finger numbness driven from the FRONT (deep below the chest muscle toward the coracoid), or from a deep ache UNDER the shoulder blade worse with coughing?",
"sublabel": "Two sources of ulnar-finger numbness - anterior medial-cord vs posterior referred C8-T1",
"answers": [
{
"id": "pmin",
"label": "Front of chest, deep toward the coracoid - pectoralis minor",
"lr": {
"pectoralis_minor": 5.5,
"serratus_posterior_superior": 0.4
}
},
{
"id": "sps",
"label": "Deep under the shoulder blade, worse coughing - serratus posterior superior",
"lr": {
"pectoralis_minor": 0.4,
"serratus_posterior_superior": 5.5
}
}
]
}
],
"treatment_dag": {
"edges": [
{
"from": "pectoralis_major",
"to": "pectoralis_minor",
"type": "functional_unit",
"label": "Pectoralis minor is almost never active without pectoralis major; treat the major first, then reassess the minor"
},
{
"from": "serratus_posterior_superior",
"to": "latissimus_dorsi",
"type": "functional_unit",
"label": "Serratus posterior superior lies beneath the latissimus over the lower ribs; examine the overlying posterior-thorax muscles together"
},
{
"from": "latissimus_dorsi",
"to": "pectoralis_major",
"type": "functional_unit",
"label": "Pseudo-thoracic-outlet group - examine latissimus, pectoralis major, teres major, and subscapularis together"
},
{
"from": "pectoralis_minor",
"to": "serratus_posterior_superior",
"type": "secondary_load",
"label": "When ulnar-finger numbness persists, reassess both the anterior (medial-cord) and posterior (sub-scapular) sources"
}
],
"edge_type_labels": {
"key_satellite": "Treat first - key TrP driving satellite",
"functional_unit": "Treat concurrently in same session",
"secondary_load": "Treat after primary resolves",
"antagonist_risk": "Treat in alternating cycles - reactive activation risk"
}
},
"emergency": [
{
"id": "rf-e1",
"label": "Acute coronary syndrome / cardiac ischaemia",
"question": "Left-sided or central chest pressure, tightness, or constriction radiating to the ulnar arm/hand, especially with exertion, breathlessness, sweating, nausea, or a cardiac history? The left pectoralis major trigger-point pattern mimics angina exactly - and relief of the pain by trigger-point treatment does NOT exclude cardiac disease. Establish cardiac status independently and urgently when this pattern is present.",
"source": "T&S Ch.42 (pectoralis major cardiac mimicry)"
},
{
"id": "rf-e2",
"label": "Acute ulnar artery occlusion / hand ischaemia",
"question": "A cold, pale, or painful ulnar hand or fingers, with reduced capillary refill or a weak/absent ulnar pulse, after trauma or repetitive hypothenar impact (using the palm as a hammer)? Ulnar artery thrombosis or aneurysm at Guyon's canal threatens the hand - needs urgent vascular assessment.",
"source": "Sanderson, Mohr & Abraham 2020; Davis & Kane"
}
],
"urgent": [
{
"id": "rf-u1",
"label": "Pancoast (superior sulcus) tumour / apical lung lesion",
"question": "Progressive deep ulnar-arm and medial-forearm pain with weight loss, a smoking history, a drooping eyelid and small pupil (Horner's), or hand intrinsic-muscle wasting? An apical lung tumour can compress the lower brachial plexus (C8-T1) and must be excluded with chest imaging - a key reason ulnar/C8 arm pain is not assumed to be myofascial without screening.",
"source": "Davis & Kane (ulnar nerve entrapment differential)"
},
{
"id": "rf-u2",
"label": "Hook-of-hamate fracture",
"question": "Ulnar wrist/hand pain and tenderness over the hypothenar eminence after a fall or a 'club/bat/racquet' impact, sometimes with ulnar-nerve symptoms in the little finger? Plain films have low sensitivity - a CT (or carpal-tunnel view) is needed. Missed hook-of-hamate fractures cause nonunion, ulnar neuropathy, and flexor-tendon rupture.",
"source": "Davis & Kane; Sanderson, Mohr & Abraham 2020"
},
{
"id": "rf-u3",
"label": "Ulnar nerve entrapment with motor loss (cubital tunnel / Guyon's canal)",
"question": "Ulnar paraesthesia of the ring and little fingers with WEAKNESS or wasting of the hand intrinsics, a positive Froment's sign, clawing of the 4th/5th fingers, or symptoms reproduced by sustained elbow flexion? Progressive motor loss (atrophy) needs prompt electrodiagnostic study and surgical consideration - outcomes worsen once axonal loss develops.",
"source": "Davis & Kane; Lleva, Munakomi et al. 2025"
},
{
"id": "rf-u4",
"label": "C8-T1 radiculopathy / neurogenic thoracic outlet syndrome",
"question": "Neck pain with dermatomal C8-T1 forearm/hand symptoms, SENSORY CHANGE IN THE MEDIAL FOREARM (above the wrist), reflex change, or thenar/intrinsic weakness, or positive thoracic-outlet provocative tests with a vascular component? Medial-forearm sensory loss points to the root or plexus rather than a peripheral ulnar nerve - and a true compressive process must be excluded.",
"source": "Lleva, Munakomi et al. 2025; Differential:ThoracicOutletSyndrome"
}
],
"broad_differential": [
{
"id": "bd-1",
"condition": "Ulnar neuropathy at the elbow (cubital tunnel syndrome)",
"confidence": "common",
"mimics": "Ulnar forearm and 4th/5th-finger pain and numbness - overlaps the latissimus, pectoral, and serratus referral directly",
"distinguishing_feature": "Paraesthesia and numbness of the little and ulnar-half of the ring finger, worse with sustained elbow flexion and at night, with a positive Tinel over the cubital tunnel and (later) weakness/wasting of the hand intrinsics, a positive Froment's sign, and clawing. Compression is usually at Osborne's ligament. Trigger-point referral produces no true weakness, no wasting, normal nerve conduction, and IS reproduced by muscle palpation.",
"action": "Examine for intrinsic weakness, Froment's, Tinel at the elbow, and elbow-flexion provocation; electrodiagnostic studies and ultrasound localise and grade the lesion. Conservative care (activity modification, night elbow-extension splinting, padding) for mild cases; decompression or transposition for progressive motor loss. Treat coexisting shoulder-girdle trigger points, which can be the dominant pain source.",
"source": "Davis & Kane; Lleva, Munakomi et al. 2025"
},
{
"id": "bd-2",
"condition": "Ulnar neuropathy at the wrist (Guyon's canal syndrome)",
"confidence": "uncommon",
"mimics": "Ulnar hand pain and numbness - overlaps the distal end of the ulnar-forearm referral",
"distinguishing_feature": "Compression in Guyon's canal, with the pattern set by the zone: zone 1 gives mixed motor and sensory loss, zone 2 a pure motor deficit (intrinsic weakness without sensory change), zone 3 a pure sensory deficit of the palmar 4th/5th fingers. The DORSAL ulnar hand is SPARED (the dorsal cutaneous branch leaves proximal to the canal) - a key sign localising the lesion to the wrist rather than the elbow. Usually caused by a ganglion, a hook-of-hamate fracture, or ulnar artery pathology. Trigger-point referral produces no fixed deficit.",
"action": "Define motor vs sensory pattern; radiographs (carpal-tunnel/oblique views) and CT for a hamate fracture, MRI/ultrasound for a ganglion or ulnar artery lesion. Excise space-occupying lesions; zone-specific decompression. Treat coexisting trigger points concurrently.",
"source": "Davis & Kane; Lleva, Munakomi et al. 2025; Shehab & Mirabelli 2013"
},
{
"id": "bd-3",
"condition": "Medial epicondylitis (golfer's elbow) / flexor-pronator tendinopathy",
"confidence": "common",
"mimics": "Medial elbow and ulnar-forearm pain - overlaps the proximal end of the ulnar-forearm zone",
"distinguishing_feature": "Gradual-onset aching and point tenderness AT or just distal to the medial epicondyle over the flexor-pronator origin, worse with resisted wrist flexion and forearm pronation; ulnar-nerve irritation may coexist (symptoms extending toward the wrist). In throwers, an acute flexor-pronator avulsion is almost always accompanied by an ulnar collateral ligament rupture. Trigger-point referral is reproduced by muscle-belly palpation, not localised to the epicondyle.",
"action": "Resisted wrist-flexion/pronation testing and epicondyle palpation; the diagnosis is clinical. Activity modification, bracing, eccentric loading; rule out ulnar collateral ligament injury in acute athletic onset. Treat coexisting forearm and shoulder-girdle trigger points.",
"source": "Hsu/Otoshi (medial epicondylitis, StatPearls)"
},
{
"id": "bd-4",
"condition": "C8-T1 cervical radiculopathy",
"confidence": "uncommon",
"mimics": "Ulnar forearm and hand pain/numbness referred from the neck - the serratus posterior superior is the commonest myofascial mimic of this",
"distinguishing_feature": "Dermatomal C8-T1 sensory change INCLUDING THE MEDIAL FOREARM (above the wrist), reflex change, and weakness of muscles beyond the ulnar nerve's territory - notably the median-innervated thenar muscles (abductor/opponens pollicis) and radial-two lumbricals, which are spared in a peripheral ulnar lesion. Positive Spurling's. Trigger-point referral produces no objective deficit, spares the medial forearm, and IS reproduced by muscle palpation.",
"action": "Full neurological and upper-quarter examination; Spurling's; MRI cervical spine and EMG/nerve conduction studies where neurological signs are present. Treat coexisting serratus posterior superior, scalene, and pectoral trigger points - they are the dominant or driving source in many mislabelled 'radiculopathies'.",
"source": "Lleva, Munakomi et al. 2025; Davis & Kane"
},
{
"id": "bd-5",
"condition": "Thoracic outlet syndrome (neurogenic / vascular)",
"confidence": "uncommon",
"mimics": "Ulnar arm and 4th/5th-finger symptoms - overlaps the pectoralis minor (medial-cord) and serratus/latissimus pseudo-TOS patterns",
"distinguishing_feature": "Lower-trunk (C8-T1) neurogenic symptoms with positive EAST/Roos and provocative tests, sometimes with vascular features (colour change, swelling, a bruit, or pulse change with arm positioning). A taut pectoralis minor can compress the brachial plexus medial cord (a myofascial pseudo-TOS), distinct from compression at the scalene triangle or a cervical rib. Trigger-point referral alone produces no vascular signs and no fixed motor deficit.",
"action": "Provocative testing (EAST/Roos, Adson's), vascular assessment, chest/cervical-spine imaging for a cervical rib, and electrodiagnostics for true neurogenic TOS. Treat the pectoralis minor and scalene trigger points; vascular or true neurogenic TOS needs specialist referral.",
"source": "Differential:ThoracicOutletSyndrome; Davis & Kane"
},
{
"id": "bd-6",
"condition": "Hook-of-hamate fracture / ulnar artery (hypothenar hammer) lesion",
"confidence": "uncommon",
"mimics": "Ulnar wrist and hand pain, sometimes with ulnar-nerve symptoms - the distal end of the region",
"distinguishing_feature": "Hypothenar tenderness and ulnar wrist/hand pain after a fall or repetitive palm impact (racquet, club, bat, or using the hand as a hammer). A hook-of-hamate fracture is poorly seen on plain films (needs a carpal-tunnel view or CT); repetitive hypothenar trauma can also thrombose the ulnar artery (hypothenar hammer syndrome), causing ischaemic ulnar-finger symptoms. Trigger-point referral has no bony tenderness or vascular change.",
"action": "Carpal-tunnel-view radiograph and CT for the hamate hook; vascular studies (ultrasound/angiography) if hypothenar hammer syndrome is suspected. Immobilise or excise the hooked fragment; vascular management for arterial occlusion.",
"source": "Davis & Kane; Sanderson, Mohr & Abraham 2020"
},
{
"id": "bd-7",
"condition": "Acute coronary syndrome / cardiac referred pain",
"confidence": "uncommon",
"mimics": "Left ulnar-arm and medial-forearm pain with chest discomfort - overlaps the left pectoralis major pattern exactly",
"distinguishing_feature": "Exertional or rest chest pressure/tightness radiating to the left ulnar arm, with breathlessness, diaphoresis, nausea, or cardiac risk factors. The pectoralis major sternal pattern mimics this in detail, and crucially, relief of the pain by vapocoolant or trigger-point treatment does NOT exclude ischaemia - the conditions coexist. Trigger-point pain is reproduced by chest-wall palpation and has no exertional ECG change.",
"action": "When the pattern is left-sided chest-and-ulnar-arm, establish cardiac status independently (ECG, troponin, risk assessment) regardless of any response to trigger-point treatment. Treat the pectoral trigger points only once cardiac disease is addressed.",
"source": "T&S Ch.42"
},
{
"id": "bd-8",
"condition": "Renal / systemic and inflammatory causes (referred and constitutional)",
"confidence": "rare",
"mimics": "A persistent posterior trunk ache that can accompany the arm pain - the serratus posterior inferior pattern can mimic renal pain, and systemic disease can present as multi-site limb pain",
"distinguishing_feature": "Costovertebral-angle tenderness, abnormal urinalysis, fever, or systemic upset point to renal or systemic disease rather than a myofascial source; inflammatory arthropathy gives swelling, prolonged morning stiffness, and multi-joint involvement. Trigger-point pain is focal, mechanically reproduced, and lacks systemic features - but a review of systems is essential when the picture is atypical or constitutional symptoms are present.",
"action": "Review of systems; urinalysis, inflammatory markers, and imaging where suggested; appropriate specialist referral. Treat coexisting trigger points concurrently.",
"source": "T&S (serratus posterior referral); general internal-medicine screen"
}
]
}